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Accelerating Growth and Development Accelerating Growth and Research and Technology for Development for Business Accelerating Growth and Development Monday, 24 May 2010 • 8:30 – 9:40 Monday, 24 May 2010 • 10:15 – 11:30 Tuesday, 25 May 2010 • 8:30 – 10:00 Naledi Pandor Reuben September Reinaldo Valenzuela Conference Chair Group Chief Executive Officer Director, Wireless Research Minister of the Department Telkom, Republic of South Africa Bell Labs, Alcatal-Lucent, USA of Science and Technology South Africa Ajay Pandey Raymond W. Yeung Managing Director & Chief Executive Officer Chair Professor Steven D. Gray Neotel, Republic of South Africa Chinese University of Hong Kong, Hong Kong Head & Vice President, Corporate Research Huawei Technologies, USA Andile Ngcaba Executive Chairman Dimension Data - Africa and Middle East, Republic of South Africa BUSINESS FORUMS Monday, 24 March 2010 Tuesday, 25 March 2010 Wednesday, 26 March 2010 Mobile Broadband as an Enabler of Regulatory Environment and Spectrum Reform Ultra Broadband Technologies Accelerated Broadband Development – the Key to Growth and Development 13:30 – 15:00 11:00 – 12:30 9:00 – 10:30 IMT-Advanced - The Technical and the Strategic Policy and Funding Models for Accelerating the 100 Gbps Networking: Trends, Deployment, and Landscape for 4G and Beyond Rollout of Broadband Access and Networks in Challenges 15:30 – 17:00 Developing Countries Alternatives to providing Affordable and Sustainable 13:30 – 15:00 Mobile Broadband in a Fast and Cost Effective Spectrum Management – Technologies, Economics, Manner Regulatory Environment 15:30 – 17:00 Challenges in Commercialization of Cognitive Radio Technologies TECHNICAL SYMPOSIA • Ad Hoc Sensor and Mesh Networking • Multimedia Services, Communications Software • Signal Processing • Communication and Information System Security and Services • Wireless Communications • Communication Theory • Next Generation Networking Protocols, and • Wireless and Mobile Networking • Communications Quality of Service, Reliability and Services • Selected Areas in Communications Performance Modeling • Optical Networks and Systems TUTORIALS > Buy one get the second one free! < T1: Cooperative Wireless Communications T11: Femto-cells: Opportunities and Challenges T2: Networking Cognitive Radios for Dynamic Spectrum Access T12: Vehicular Networking T3: Broadband Wireless Technologies: LTE and WiMax T13: Aspects of Multiuser MIMO-Principles and Standardization in LTE-Advanced T4: Locality Aware P2P Delivery: The Way to Scale Internet Video T14: Understanding Next Generation Mobile Networks (NGMN): The Role of the T5: Energy Efficient Networks Evolved Packet Core (EPC) for seamless Mobile Broadband Service Provision T6: High-Definition Location-Awareness T15: Multi Gigabit Transmissions at 60 GHz: Standards, Technologies, and Challenges T7: Compressive Sensing and Signal Scarcity in WirelessCommunications T16: Stochastic Geometry and Random Graphs for the Analysis and Design of T8: Application of Game Theory for Designing Cognitive Radio Networks Wireless Networks T9: Statistical Delay-QoS Provisioning in Wireless Networks: Effective Capacity T17: Recovery in IP over Optical Networks: Challenges and Solutions and QoS-Driven Resource Allocations T18: Overview of 3GPP LTE Radio Interface: Layers 2/3 T10: Planning Wireless Municipal Networks based on Wi-Fi/WiMax Mesh Networks - T19: Security Issues in Dynamic Spectrum Access Networks Applications, Technologies and Business Models T20: Biologically-inspired and Nano-scale Communication and Networking WORKSHOPS W1: Smart Grid Communications W6: Cooperative and Cognitive Mobile Networks W2: Energy Efficiency in Wireless Networks & Wireless Networks for Energy W7: Cognitive Radio Interfaces and Signal Processing Efficiency W8: Medical Applications Networking W3: Vehicular Connectivity W9: IEEE Vehicular Networking and Applications: Future Wireless W4: Social Networks Technologies for Vehicle Infrastructure Integration (VII) Applications W5: Underwater Networks W10: Integrated Disaster Risk Management for Africa

Director of Magazines Andrzej Jajszczyk, AGH U. of Sci. & Tech. (Poland) Editor-in-Chief IEEE Steve Gorshe, PMC-Sierra, Inc. (USA) Associate Editor-in-Chief Sean Moore, Avaya (USA) Senior Technical Editors Tom Chen, Swansea University (UK) MAGAZINE Nim Cheung, ASTRI (China) Nelson Fonseca, State Univ. of Campinas (Brazil) April 2010, Vol. 48, No. 4 Torleiv Maseng, Norwegian Def. Res. Est. (Norway) Peter T. S. Yum, The Chinese U. Hong Kong (China) www.comsoc.org/~ci Technical Editors Sonia Aissa, Univ. of Quebec (Canada) RESIDENT S AGE YEONG I EE Mohammed Atiquzzaman, U. of Oklahoma (USA) 6 P ’ P /B G L Paolo Bellavista, DEIS (Italy) 10 SOCIETY NEWS/COMSOC MEMBERS NAMED TO FELLOW GRADE Tee-Hiang Cheng, Nanyang Tech. U. (Rep. Singapore) Jacek Chrostowski, Scheelite Techn. LLC (USA) 14 CONFERENCE CALENDAR Sudhir S. Dixit, Nokia Siemens Networks (USA) Stefano Galli, Panasonic R&D Co. of America (USA) 16 NEW PRODUCTS Joan Garcia-Haro, Poly. U. of Cartagena (Spain) LOBAL OMMUNICATIONS EWSLETTER DITED BY TEFANO REGNI Vimal K. Khanna, mCalibre Technologies (India) 19 G C N /E S B Janusz Konrad, Boston University (USA) Abbas Jamalipour, U. of Sydney (Australia) DESIGN AND IMPLEMENTATION: IMS APPLICATIONS AND SUPPORT Deep Medhi, Univ. of Missouri-Kansas City (USA) Nader F. Mir, San Jose State Univ. (USA) SERIES EDITOR: SEAN MOORE Amitabh Mishra, Johns Hopkins University (USA) GUEST EDITORIAL Sedat Ölçer, IBM (Switzerland) 24 Glenn Parsons, Ericsson Canada (Canada) 26 IMS SERVICE DEVELOPMENT API AND TESTBED Harry Rudin, IBM Zurich Res.Lab. (Switzerland) Hady Salloum, Stevens Institute of Tech. (USA) The authors explore the architectural and protocol aspects that enable third-party Antonio Sánchez Esguevillas, Telefonica (Spain) IMS application development and deployment. They also study how the applications Heinrich J. Stüttgen, NEC Europe Ltd. (Germany) will coexist with other applications already deployed in the IMS. They describe Java Dan Keun Sung, Korea Adv. Inst. Sci. & Tech. (Korea) libraries exploiting the functionality of the IMS both in the terminal client and Danny Tsang, Hong Kong U. of Sci. & Tech. (Japan) within the core network. Series Editors SALVATORE LORETO, TOMAS MECKLIN, MILJENKO OPSENICA, AND HEIDI-MARIA RISSANEN Ad Hoc and Sensor Networks Edoardo Biagioni, U. of Hawaii, Manoa (USA) DEPLOYMENT OF CONTEXTUAL CORPORATE TELCO SERVICES BASED ON Silvia Giordano, Univ. of App. Sci. (Switzerland) 34 Automotive Networking and Applications PROTOCOL ADAPTATION IN THE NGN ENVIRONMENT Wai Chen, Telcordia Technologies, Inc (USA) The authors present a practical deployment of a contextual service offered by a Luca Delgrossi, Mercedes-Benz R&D N.A. (USA) Timo Kosch, BMW Group (Germany) convergent telecommunications operator, whose functionality is to provide Tadao Saito, University of Tokyo (Japan) intelligent context-based call routing and rerouting, orchestrated from the operator’s Design & Implementation service layer. It is based on IMS control layer capabilities to properly capture the Sean Moore, Avaya (USA) situation of the end user in a ubiquitous coverage area. Integrated Circuits for Communications Charles Chien (USA) ALEJANDRO CADENAS, ANTONIO SANCHEZ-ESGUEVILLAS, AND BELÉN CARRO Zhiwei Xu, SST Communication Inc. (USA) Stephen Molloy, Qualcomm (USA) 42 THE DESIGN AND IMPLEMENTATION OF ARCHITECTURAL COMPONENTS FOR Network and Service Management Series THE INTEGRATION OF THE IP MULTIMEDIA SUBSYSTEM AND WIRELESS George Pavlou, U. of Surrey (UK) Aiko Pras, U. of Twente (The Netherlands) SENSOR NETWORKS Topics in Optical Communications The authors have previously proposed a presence-based architecture for WSN/IMS Hideo Kuwahara, Fujitsu Laboratories, Ltd. (Japan) Osman Gebizlioglu, Telcordia Technologies (USA) integration. This architecture relies on two key components: a WSN/IMS gateway John Spencer, Optelian (USA) acting as an interworking unit between WSNs and the IMS; and an extended presence Vijay Jain, Verizon (USA) server serving as a context information management node in the core network. In Topics in Radio Communications this article the authors focus on the design and implementation of these two Joseph B. Evans, U. of Kansas (USA) Zoran Zvonar, MediaTek (USA) components. Standards MAY EL BARACHI, ARIF KADIWAL, ROCH GLITHO, FERHAT KHENDEK, RACHIDA DSSOULI Yoichi Maeda, NTT Adv. Tech. Corp. (Japan) Mostafa Hashem Sherif, AT&T (USA) 52 BROADBAND INTERNET IN EU COUNTRIES: LIMITS TO GROWTH Columns The author provides an analysis of broadband Internet diffusion in 27 countries of Book Reviews the European Union. The author also proposes a simple model of its growth and Andrzej Jajszczyk, AGH U. of Sci. & Tech. (Poland) History of Communications identifies the theoretical growth limits in each country. Some aspects of the Mischa Schwartz, Columbia U. (USA) European i2010 project implementation are presented, discussed, and compared Regulatory and Policy Issues with the model. J. Scott Marcus, WIK (Germany) RYSZARD STRUZAK Jon M. Peha, Carnegie Mellon U. (USA) Technology Leaders' Forum SERVICE TRAFFIC MANAGEMENT SYSTEM FOR MULTISERVICE IP NETWORKS: Steve Weinstein (USA) 58 Very Large Projects LESSONS LEARNED AND APPLICATIONS Ken Young, Telcordia Technologies (USA) Your Internet Connection Next-generation networks offer new opportunities and challenges to Internet service Eddie Rabinovitch, ECI Technology (USA) providers as well as providers of other online services. Service providers can now Publications Staff deploy new services over an IP network infrastructure without building their own Joseph Milizzo, Assistant Publisher networks. In an open network environment, the network resources of ISPs should Eric Levine, Associate Publisher be fairly open to third parties that plan to launch their own services. To respond to Susan Lange, Digital Production Manager the changing network paradigm, it is essential to measure the traffic of individual Jennifer Porcello, Production Specialist Catherine Kemelmacher, Associate Editor services, and to estimate their cost for cost accounting between service provider and Devika Mittra, Publications Assistant ISP. However, current traffic measurement techniques only provide total traffic volume in links, without reporting the operator whose services flow through the links. JUNGYUL CHOI, SEUNG-HOON KWAK, MI-JEONG LIM, TAEIL CHAE, BYOUNG-KWON SHIM, AND ® JAE-HYOUNG YOO

2 IEEE Communications Magazine • April 2010

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SAFETY ASSURANCE AND RESCUE COMMUNICATION SYSTEMS IN 2010 Communications Society 66 Elected Officers HIGH-STRESS ENVIRONMENTS: A MINING CASE STUDY Byeong Gi Lee, President Effective communication is critical to the success of response and rescue operations. Doug Zuckerman, Past President However, unreliable operation of communication systems in high-stress environments Mark Karol, VP–Technical Activities Khaled B. Letaief, VP–Conferences is a significant obstacle to achieving this. The contribution of this article is threefold. Sergio Benedetto, VP–Member Relations First, it outlines those common characteristics that impair communication in high- Leonard Cimini, VP–Publications stress environments and then evaluates their importance, specifically in the Members-at-Large underground mine environment. Second, it discusses current underground mine Class of 2010 communication techniques and identifies their potential problems. Third, it explores Fred Bauer, Victor Frost the design of wireless sensor network based communication and location sensing Stefano Galli, Lajos Hanzo systems that could potentially address current challenges. Class of 2011 PRASANT MISRA, SALIL KANHERE, DIETHELM OSTRY, AND SANJAY JHA Robert Fish, Joseph Evans Nelson Fonseca, Michele Zorzi TOPICS IN INTEGRATED CIRCUITS FOR COMMUNICATIONS Class of 2012 SERIES EDITORS: CHARLES CHIEN, ZHIWEI XU, AND STEPHEN MOLLOY Stefano Bregni, V. Chan Iwao Sasase, Sarah K. Wilson 74 GUEST EDITORIAL 2010 IEEE Officers 76 VIDEO ENCODER DESIGN FOR HIGH-DEFINITION 3D VIDEO COMMUNICATION Pedro A. Ray, President Moshe Kam, President-Elect SYSTEMS David G. Green, Secretary The authors present an overview of 3D video coding standards developments and Peter Staecker, Treasurer John R. Vig, Past-President design challenges of an MVC encoder. Then the algorithm and architecture E. James Prendergast, Executive Director optimization schemes are proposed. For the trade-off between system memory Nim Cheung, Director, Division III bandwidth and on-chip memory size, a cache-based prediction engine is proposed IEEE COMMUNICATIONS MAGAZINE (ISSN 0163- to ease both design challenges. 6804) is published monthly by The Institute of Electrical and PEI-KUEI TSUNG, LI-FU DING, WEI-YIN CHEN, TZU-DER CHUANG, YU-HAN CHEN, PAI-HENG HSIAO, Electronics Engineers, Inc. Headquarters address: IEEE, 3 Park Avenue, 17th Floor, New York, NY 10016-5997, USA; SHAO-YI CHIEN, AND LIANG-GEE CHEN tel: +1-212-705-8900; http://www.comsoc. org/ci. Responsibility for the contents rests upon authors of N MBEDDED NM ASEBAND Z Z UAL signed articles and not the IEEE or its members. Unless oth- 88 A E 65 CMOS B IQ 48 MH –1 GH D erwise specified, the IEEE neither endorses nor sanctions any UNER FOR positions or actions espoused in IEEE Communications T DOCSIS 3.0 Magazine. The authors present an embedded CMOS digital dual tuner for DOCSIS 3.0 and ANNUAL SUBSCRIPTION: $27 per year print subscrip- set-top box applications. The dual tuner down-converts a total of ten 6 MHz Annex B tion. $16 per year digital subscription. Non-member print channels or eight 8 MHz Annex A channels, for a maximum data rate of 320 Mb/s in subscription: $400. Single copy price is $25. Annex B and 400 Mb/s in Annex A mode. EDITORIAL CORRESPONDENCE: Address to: Editor- FRANCESCO GATTA, RAY GOMEZ, YOUNG SHIN, TAKAYUKI HAYASHI, HANLI ZOU, JAMES Y.C. CHANG, in-Chief, Nim K. Cheung, Telcordia Tech., Inc., One Telcordia Drive, Room RRC-1B321, Piscataway, NJ 08854- LEONARD DAUPHINEE, JIANHONG XIAO, DAVE S.-H. CHANG, TAI-HONG CHIH, MASSIMO BRANDOLINI, 4157; tel: +(732) 699-5252, e-mail: [email protected]______. DONGSOO KOH, BRYAN J.-J. HUNG, TAO WU, MATTIA INTROINI, GIUSEPPE CUSMAI, ERTAN ZENCIR, COPYRIGHT AND REPRINT PERMISSIONS: FRANK SINGOR, HANS EBERHART, LOKE TAN, BRUCE CURRIVAN, LIN HE, PETER CANGIANE, Abstracting is permitted with credit to the source. Libraries are permitted to photocopy beyond the limits of U.S. AND PIETER VORENKAMP Copyright law for private use of patrons: those post-1977 articles that carry a code on the bottom of the first page pro- 98 INTEGRATED ELECTRONIC SYSTEM DESIGN FOR AN IMPLANTABLE WIRELESS vided the per copy fee indicated in the code is paid through BATTERYLESS BLOOD PRESSURE SENSING MICROSYSTEM the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For other copying, reprint, or republi- A wireless, batteryless, less invasive blood pressure sensing microsystem based on cation permission, write to Director, Publishing Services, an instrumented circular cuff has been developed for advanced biological research. at IEEE Headquarters. All rights reserved. Copyright © 2010 The proposed sensing technique avoids vessel penetration and substantially by The Institute of Electrical and Electronics Engineers, Inc. POSTMASTER: Send address changes to IEEE minimizes vessel restriction due to the soft cuff elasticity. Communications Magazine, IEEE, 445 Hoes Lane, PENG CONG, WEN H. KO, AND DARRIN J. YOUNG Piscataway, NJ 08855-1331. GST Registration No. 125634188. Printed in USA. Periodicals postage paid at New 106 POWER LINE COMMUNICATION NETWORKS FOR LARGE-SCALE CONTROL AND York, NY and at additional mailing offices. Canadian Post International Publications Mail (Canadian Distribution) AUTOMATION SYSTEMS Sales Agreement No. 40030962. Return undeliverable Power line communications uses the existing power line infrastructure for Canadian addresses to: Frontier, PO Box 1051, 1031 Helena communication purposes. While the majority of recent contributions have discussed Street, Fort Eire, ON L2A 6C7 PLC for high-data-rate applications like Internet access or multimedia communication SUBSCRIPTIONS, orders, address changes — IEEE Service Center, 445 Hoes Lane, Piscataway, NJ serving a relatively small number of users, in this article the authors are concerned 08855-1331, USA; tel: +1-732-981-0060; e-mail: with PLC as an enabler for sensing, control, and automation in large systems address.change@______ieee.org. comprising tens or even hundreds of components spread over relatively wide areas. ADVERTISING: Advertising is accepted at the dis- GERD BUMILLER, LUTZ LAMPE, AND HALID HRASNICA cretion of the publisher. Address correspondence to: Advertising Manager, IEEE Communications Magazine, IMS-COMPLIANT MANAGEMENT OF VERTICAL HANDOFFS FOR MOBILE 3 Park Avenue, 17th Floor, New York, NY 10016. 114 ULTIMEDIA ESSION ONTINUITY SUBMISSIONS: The magazine welcomes tutorial or M S C survey articles that span the breadth of communica- The authors propose an original solution for session continuity based on the primary tions. Submissions will normally be approximately 4500 design guideline of cleanly and effectively separating the signaling plane (for session words, with few mathematical formulas, accompanied by up to six figures and/or tables, with up to 10 carefully reconfiguration via SIP) from the media delivery plane (data transmission and related selected references. Electronic submissions are pre- handoff management operations). Our optimized handoff management techniques ferred, and should be sumitted through Manuscript exploit terminal-based decentralized predictions to minimize service-level handoff delays. Central (http://commag-ieee.manuscript ______central.com/). Instructions can be found at: http://___ PAOLO BELLAVISTA, ANTONIO CORRADI, AND LUCA FOSCHINI ______www.comsoc.org/pubs/commag/sub_guidelines.html. For further information contact Steve Gorshe, 122 REPUTATION ESTIMATION AND QUERY IN PEER-TO-PEER NETWORKS Associate Editor-in-Chief (steve_gorshe@pmc-______Many peer-to-peer systems assume that peers are cooperative to share and relay data. _____sierra.com). All submissions will be peer reviewed. But in the open environment of the Internet, there may be uncooperative malicious peers. To detect malicious peers or reward well behaved ones, a reputation system is often used. The authors give an overview of P2P reputation systems and investigate two fundamental issues in the design: reputation estimation and query. They classify the state-of-the-art approaches into several categories and study representative examples in each category. XING JIN AND S.-H. GARY CHAN

4 IEEE Communications Magazine • April 2010

THE PRESIDENT’S PAGE

TECHNICAL ACTIVITIES: STIMULATING TECHNICAL CONTENT CREATION

echnical Activities is the foundation pation. Long-time members might already be T for many of the Communications Soci- familiar with many of the products, services, ety’s products and services, while also pro- and opportunities offered by ComSoc. This is viding “community” and “networking” not so for the new members whom we need opportunities for its participants. ComSoc’s to attract and involve so that we can continue Technical Activities community establishes to grow and thrive in the coming years. an environment for technical content cre- Through various means, we plan to publicize ation, whereas Publications and Confer- and make known “open call” opportunities ences deal with the presentation and for all individuals to actively participate and conversion of technical content into techni- serve in ComSoc. Also, recognizing the cal products and services. Within ComSoc, changing and evolving technological land- the term “technical activities” encompasses scape, we will strive to stay relevant and pro- a wide range of topics: technical commit- vide more technical activities of interest to tees, emerging technologies, awards, educa- BYEONG GI LEE potential members from industry. tion, standards, distinguished lecturers, evaluation of IEEE Fellow nominations, TECHNICAL COMMITTEES and communications history. These areas We currently have 25 Technical Commit- continue to evolve in spite of and in the face tees (TCs), including comparatively young of cuts in important parts of the ComSoc TCs such as those on Cognitive Networks budget (due to the economic downturn). As and Power-Line Communications, and the mentioned in the January 2010 message, we most recent addition, e-Health, created in will strive to maintain and improve upon the 2009. TCs help define and implement the technical quality of ComSoc products and technical directions of the Society. They help services, providing value to our members, organize and ensure the technical quality of benefiting the broader communications and workshops and conference sessions, evaluate networking community, and ultimately doing and endorse proposals for new events, help our part in achieving ComSoc’s goal of implement publications, define and promote “Serving Humanity” – for example, helping industry standards, and provide many pro- serve fundamental human needs for content fessional networking opportunities. and communications. MARK KAROL A list of ComSoc TCs and their officers Sharing this month’s column is Mark is at http://ww2.comsoc.org/about/commit- Karol, ComSoc’s Vice President — Techni- ___tees/ Technical. You can learn much more cal Activities. Mark received his Ph.D. in electrical engi- about the TCs by following the links to their respective TC neering from Princeton University in 1986 and is an IEEE websites. Please visit the websites of the TCs of your inter- Fellow. From 1985 until 2000 he was a member of the est, contact the officers with your questions, and volunteer Research Communications Sciences Division at Bell Labo- to help them in their endeavors. Participation in one or ratories. From 2000 until 2008, he was a research scientist more TCs will move you into an exciting technical life, with Avaya Labs. Since 2008, he has been a senior scientist where you can enjoy networking and co-working with col- in Applied Research at Telcordia Technologies. Mark leagues having common technical interests. received the Society’s Donald W. McLellan Meritorious So that the TCs stay current in technical topics and Service Award in 2005, and has served as Associate Editor content, we have mechanisms to control the entry and exit for the Journal of Lightwave Technology, General Chair of of TCs, with the former performed by the Emerging Tech- two major IEEE conferences, ICC ’02 and INFOCOM ’94, nologies Committee (see the next section) and the latter ComSoc’s Chief Information Officer (CIO), Director of by the TC Recertification Committee (TCRC). To ensure Magazines, and Vice President — Conferences. In 2006- that TCs maintain high quality standards and stay respon- 2007, Mark was elected by ComSoc members to serve on sive to the interests of our technical community, the the IEEE Board as Division III Director, representing TCRC, chaired by VP-Technical Activities, Mark, evalu- Communications Technology. ates each TC once every three years and recommends to In the rest of this article, Mark and I provide a brief the Board of Governors whether to re-certify or terminate overview of the many technical activities within ComSoc and it. For the recertification, the TCRC reviews the overall the distinguished individuals that lead the efforts. In all of TC structure and evaluates the accomplishments, visions, these activities, there are opportunities in 2010–2011 to and goals of each TC. The TCRC may also recommend implement the “ComSoc Golden Triangle” vision of Global- that the Board of Governors create new TCs if it sees a ization, development of Young Leaders, and Industry partici- gap in current coverage of technical areas.

6 IEEE Communications Magazine • April 2010

THE PRESIDENT’S PAGE

EMERGING TECHNOLOGIES with other IEEE education programs. Stefano Bregni We encourage and provide assistance to members with serves as Director of Education. common interest in a new technology area to form a small Examples of ComSoc educational programs include online activity group, called a sub-committee, with the expecta- webinars and tutorials (e.g., the Tutorials NowTM program tion that such a group may eventually evolve into a techni- features more than 90 titles), conventional tutorials at confer- cal committee. The Emerging Technologies Committee, ences, and courses especially tailored to cover certification chaired by Naohisa Ohta, helps identify and nurture new program topics (e.g., in Wireless Communications Engineer- technical directions, and approves the formation of sub- ing Technologies (WCET)). Working groups on the Educa- committees. The goal is timely dissemination of technical tion Board are working on specific tasks to monitor and information in emerging technology areas that are of high enhance all ComSoc educational products and services; for interest to our members and others in our field. example, exploring ways of virtual collaboration for e-teaching. Current technical subcommittees are: (i) Applications of Globalization is a major value. Online tutorials and On- Nanotechnologies in Communications; (ii) Autonomic Com- Line Distinguished Lectures are an excellent example of Com- munications; (iii) Consumer Networking; (iv) Human Centric Soc’s efforts to facilitate participation by student chapters and Communications; (v) Integrated Fiber & Wireless Technolo- from disadvantaged areas. We will continue to search for new gies; (vi) Nano-Scale, Molecular, & Quantum Networking; educational opportunities, including development of products and (vii) Peer-to-Peer Networking. More information about aimed at students — our future Young Leaders. the technical subcommittees is at http://ww2.comsoc.org/about/ STANDARDS ______committees/emerging. Discussion is also under way regarding new opportunities in other new technological areas, such as ComSoc sponsors standards activities to meet the needs smart grids (for the power industry), vehicular networking, of our members and the worldwide communications indus- and intelligent transportation systems. You may write a pro- try. The main goal of ComSoc’s standards activities is the posal to the ETC Chair if you identify a new emerging area development of technically excellent and widely adopted that should be of interest to ComSoc. standards in communications, networking, and related fields. Standards projects of interest to ComSoc include AWARDS issues related to power-line communications, broadband Awards, as well as Fellow evaluation and Distinguished over power-line networks, smart grid technologies, Ether- Lecturer selection, are auxiliary technical functions that net passive optical networks, and fundamental aspects of establish an environment for technical activities by recog- telephony. ComSoc provides procedural guidelines, discus- nizing distinguished achievements. The Awards Committee sion forums, and support services for approved standards receives nominations and evaluates candidates for Com- activities. A detailed description of standards activities is Soc-level awards to select recipients. Vince Poor is Chair available at http://ww2. comsoc.org/about/documents/ of the Awards Committee. There are four Career Awards, pp/5.14._____ four Service Awards, and nine Paper Awards. Career ComSoc standards activities are conducted at the initia- Awards recognize career-long achievements, Service tive of members and/or organizations within the Society, or Awards recognize distinguished services to ComSoc, and of individuals or entities outside of the society. The activities Paper Awards recognize the best papers published in vari- are led by the Director of Standards, Curtis Siller, who ous ComSoc journals and magazines. helps influence and guide standards development. The stan- A complete list of the ComSoc-level awards is at dards development activity is conducted in partnership with http://ww2.comsoc.org/about/memberprograms/comsoc- the IEEE Standards Activities organization, with appropri- _____awards. Please look at the list and consider nominating ate liaison with and contributions to other standards bodies. worthy candidates for the awards. The process (including By their very nature, standards activities engage industry deadlines) for nominating candidates is included in a link participation in ComSoc. In consideration of the importance on the ComSoc website. Award winners are typically of standards as an ultimate product of technical findings and announced during ceremonies at our annual ICC and also the significant influence of standards on industry, we GLOBECOM conferences. We try to widely publicize the are carefully studying the possibility of upgrading ComSoc’s nomination deadlines so that appropriate candidates are standards activities to Vice President level. brought to the attention of the Awards Committee. If you know someone worthy of an award, please take the initia- SELECTION OF DISTINGUISHED LECTURERS tive and nominate them — don’t assume someone else will. ComSoc selects Distinguished Lecturers who will provide lectures to audiences arranged by ComSoc Chapters EDUCATION all over the world. The Distinguished Lecturers Program ComSoc’s Education activities apply our technical prod- (DLP) is one of a large set of membership programs, devel- ucts and services to educational purposes. The ComSoc oped for the benefit of the members (and others in our Education Board is responsible for establishing policies field). Distinguished Lecturer Tours, especially when con- and setting strategic directions for all continuing education ducted in developing countries, help implement ComSoc’s products and services. It is also responsible for maintaining vision of globalization and fosters ComSoc’s mission of pre- the vitality and quality of existing programs, assuring that sentation and exchange of information among its members such programs continue to meet the current needs of and technical communities throughout the world. A DLT members (and others), and coordinating ComSoc efforts can often help generate ComSoc membership and the for-

IEEE Communications Magazine • April 2010 7

THE PRESIDENT’S PAGE

mation of new Chapters. Selection of Distinguished Lectur- neer/scientist, or technical leader. The total number of new ers is performed by the Distinguished Lecturers Selection IEEE Fellows in any one year is at most one-tenth of one Committee, which is chaired by the Vice-Chair and Secre- percent of the IEEE voting membership (i.e., several hun- tary of the Technical Activities Council, Mehmet Ulema. dred new Fellows per year). Further information (includ- As in other programs of ComSoc, we have an “open ing qualifications and deadlines) about the IEEE Fellow call” nomination process for Distinguished Lecturers; infor- program is available at http://www.ieee.org/fellows. mation is available at http://ww2.comsoc.org/ about/docu- A key part of the selection process is the evaluation of ments/pp/6.8. Currently ComSoc has 19 Distinguished candidates by each of the IEEE’s Technical Societies. In Lecturers (DLs), as listed at http://ww2.comsoc. ComSoc, the Fellow Evaluation Committee, chaired by org/about/memberprograms/distinguished-lecturers. There Russell Hsing, reviews and evaluates all candidates identi- also is a link to a list of past Distinguished Lecturers and fied as working in our fields of interest. The evaluations, their topics, who are encouraged to continue giving lectures including a rank order of the candidates and a summary of (after their two-year terms have expired) in conjunction the evaluation of each candidate, are then forwarded to with business trips or events that happen to bring them to the IEEE Fellow Evaluation Committee. For further infor- ComSoc Chapters of interest. We also have recorded a mation about the Fellow Evaluation Committee, refer to

small, but hopefully growing, number of On-Line Distin- http://ww2.comsoc.org/about/______documents/pp/6.2. guished Lectures (see the above-referenced website). COMMUNICATIONS HISTORY EVALUATION OF IEEE FELLOW NOMINATIONS Communications History is a special auxiliary function of IEEE Fellow status is granted to a person with an technical activities. It deals with the history of communica- extraordinary record of accomplishments in any of the tions technology, recognizing milestones of technological IEEE’s designated fields of interest. The honor is con- development. This function is conducted by the Communica- ferred by the IEEE Board of Directors. It is one of the tions History Committee, chaired by Mischa Schwartz. This highest honors that can be bestowed upon an individual by committee is responsible for identifying, placing in electronic the Institute. It recognizes important contributions as an archives, and raising public awareness through all appropriate application engineer/practitioner, educator, research engi- steps on the most important facts/persons/achievements of communications history in particular, as well as telecommunication milestones in general. One important activity of this committee is the regular publication of “History of Communications” articles in IEEE Communications Magazine. In addition, the committee has organized special sessions on “communications history” at recent IEEE GLOBECOM conferences. More are planned for the future. Please contact Mischa if you happen to find any important findings in communications history that have not been duly recognized.

In summary, technical activities covers a wide range of programs and helps form the backbone of the IEEE Com- munications Society. We are fortunate to have an experienced and dedicated group of individuals who help lead and guide the various activities. However, we always welcome new volunteers to join us and make our programs even better. In keeping with ComSoc’s Gold- en Triangle vision, we especially encourage additional participation by young members and industrial participants — from all parts of the world. A good first step is to join a Technical Committee (which is easy to do and has no membership fees); many of the current Com- Soc leaders got their start by ______volunteering to help in ComSoc TCs.

8 IEEE Communications Magazine • April 2010

______until June 30 2010

Presented at IEEE GLOBECOM 2009 by Ali Akansu

Discrete Fourier Transform (DFT) has been the center piece of popular technologies spanning xDSL based high-speed Internet access to OFDM based wireline and wireless communications. This tutorial reviews the recently introduced non linear phase Generalized DFT, which offers significant improvements over linear phase DFT. Examples include Adaptive GDFT's ability to mitigate degradation of RF power amplifier performance and Bit Error Rate Performance. Several efficient GDFT design methods and their performance in real-world communications scenarios are highlighted.

FREE ACCESS SPONSORED BY

For other sponsor opportunities, please contact Eric Levine, Associate Publisher Phone: 212-705-8920, E-mail: [email protected]

SOCIETY NEWS

SOCIETY MEMBERS NAMED TO FELLOW GRADE MARC GOLDBURG Election to the grade of IEEE Fellow is one of the highest honors that can be For leadership in the bestowed upon our members by the Institute in recognition of their technical, educational, development and and leadership achievements. Only a select few IEEE members earn this prestigious commercialization honor. of spectrally efficient Congratulations to the following Communications Society members for their elec- wireless tion to the grade of Fellow of the IEEE. They now join company with a truly distin- communications guished roster of colleagues. systems.

RAJ ACHARYA ZHIZHANG (DAVID) CHEN JOSEPH HELLERSTEIN For contributions to For contributions to For contributions to biomedical imaging time-domain control engineering and bioinformatics. electromagnetic for performance modeling and management of simulation. computing systems.

EITAN ALTMAN ROY CIDECIYAN SHIVKUMAR KALYANARAMAN For contributions For contributions to For contributions to to analysis, signal processing and traffic management optimization, and constrained coding in computer control of for magnetic communication telecommunication recording. networks. networks.

JOSEPH BERTHOLD THOMAS CLOONAN POOI-YUEN KAM For leadership For leadership in For contributions to in optical development of cable receiver design and internetworking. modem termination performance analysis systems. for wireless communications.

EDGAR CALLAWAY ROBERT DOVERSPIKE YOSHIO KARASAWA For contributions to For contributions For contributions wireless sensor to architectures, to the measurement networks and low modeling, and and modeling of power design optimization of propagation effects in techniques for telecommunication radio communication communications networks. systems. devices and systems.

HSIAO-HWA CHEN HESHAM EL-GAMAL GERHARD KRAMER For contributions to For contributions For contributions to radio resource to multiple-input coded modulation, allocation in code multiple-output and iterative decoding, division multiple cooperative and cooperative wireless systems. communications. communications.

10 IEEE Communications Magazine • April 2010

SOCIETY NEWS

UWE KRAUS STAN LUMISH HARRY PERROS For contributions to For leadership in the For contributions to digital television development and performance signal compression implementation of evaluation modeling and transmission. commercial of computer terrestrial lightwave networks. systems.

MARWAN KRUNZ TADASHI MATSUMOTO CHUNMING QIAO For contributions For contributions For contributions to to resource to signal processing optical and wireless management policies for wireless network architectures in wireless networks. communications. and protocols.

CHANG-HEE LEE VICTOR MILLER RAMESH RAO For contributions to For contributions For leadership wavelength division to elliptic curve in wireless multiplexed-passive cryptography. communications. optical network.

PING LI JOSEPH MITOLA A. L. NARASIMHA REDDY For contributions to For contribution to For contributions to iterative signal software-defined and multimedia storage processing, multi-user cognitive radio and network support. detection and technologies. concatenated error control codes.

WANJIUN LIAO PRASANT MOHAPATRA LESLIE RUSCH For contributions to For contributions to For contributions in communication the quality of service optical and wireless protocols in provisioning in communications multimedia computer networks. systems. networking.

JOHN C.S. LUI ARIA NOSRATINIA CHRISTIAN SCHLEGEL For contributions to For contributions For contributions performance to multimedia to iterative modeling and analysis and wireless demodulation and of storage communications. decoding in wireless communication communication. systems and peer-to- peer networks.

IEEE Communications Magazine • April 2010 11

SOCIETY NEWS

ROBERT SCHOBER MILICA STOJANOVIC CHENGSHAN XIAO For contributions For contributions to For contributions to to wireless underwater acoustic channel modeling communications. communications. and signal processing for wireless communications.

DAN SCHONFELD HEINRICH STUTTGEN HOWARD YANG For contributions For leadership in For leadersip in to image and industrial research. mixed-signal video analysis. integrated circuit design and manufacturing.

MARK SHAYMAN WEI SU FENG ZHAO For contributions to For leadership For contributions to the theory of Riccati in military networked embedded equations and communications and computing and discrete-event electronic warfare sensor networks. dynamic systems. technologys.

ANDREW SINGER EMMANOUIL M. TENTZERIS WENWU ZHU For contributions to For contributions to For contributions signal processing three dimensional to video techniques for digital conformal integrated communications communication. devices for wireless over the internet communications and wireless. and sensing.

VISHWANATH SINHA NIAN-FENG TZENG ZORAN ZVONAR For contributions to For contributions to For leadership in the electrical engineering parallel computer development of education. systems and digital signal scalable routers. processing software and hardware for wireless cellular communication.

PETER STEENKISTE NITIN VAIDYA MAHESH VARANASI For contributions to For contributions to For contributions to multi-user and optimization and wireless networking wireless communication theory. monitoring protocols and mobile techniques for communications. distributed communication systems.

12 IEEE Communications Magazine • April 2010

CONFERENCE CALENDAR

2 0 1 0 Dallas, TX. Info:______http://www.ewi.info/world- Faro-Algarve, Portugal. Info: ______http://noc-con- ______wide-cybersecurity-summit ______ference.com/

A P R I L z IEEE LAN/MAN 2010 - 17the IEEE • HPSR 2010 - 2010 Int’l. Conference Workshop on Local and Metropoli- on High Performance Switching and tan Area Networks, 5-7 May Routing, 14-16 June • ICT 2010 – 17th Int’l. Conference on Long Branch, NJ. Info: http://www.ieee- Dallas, TX. Info: http://opnear.utdallas/edu/ Telecommunications, 4–7 April ______lanman.org______activ/hpsr2010/index.html______Doha, Qatar. Info: http://www.qu.edu.qa/ ______ICT2010/index.php • ISWPC - Int’. Symposium on Wire- • APSITT 2010 - 8th Asia-Pacific Sym- less Pervasive Computing, 5-7 May posium on Information and Telecom- z IEEE DYSPAN 2010 – IEEE Int’l. Modena, Italy. Info: http://www.iswpc.org/ munication Technologies, 15-18 June Symposium on Dynamic Spectrum Kuching, Malaysia. Info: http://www.ieice.org/ ___2010/ Access Networks, 6–9 April ~in_ac/APSITT/2010 Singapore. Info: http://www.ieee-dyspan.org ______z IEEE CTW 2010 - 2010 IEEE Com- z IEEE IWQOS 2010 - 18th IEEE Int’l. • WAMICON 2010 – IEEE Wireless and munication Theory Workshop, 10- Workshop on Quality of Service, 16- Microwave Technology Conference, 12 May 18 June 12–13 April Cancun, Mexico. Info: http://www.ieee- Beijing, China. Info: ______http://www.ieee- Melbourne, FL. Info: ______http://www.wami- ______ctw. iwqos.org/______con.org/ __org/ • ICUFN 2010 - 2nd Int’l. Conference • IEEE SARNOFF 2010 - 23rd IEEE • CNSR 2010 - Communication Net- on Ubiquitous Networks and Future SARNOFF Symposium 2010, 12-14 works and Services Research 2010 Networks, 16-18 June April Conference, 12-14 May Juju Island, Korea. Info: http://www.icufn.org/ Princeton, NJ. Info: http://ewh.ieee.org/r1/ Montreal, Canada. Info: http://cnsr.info/ ______princeton-centraljersey/2010_Sarnoff_Sym- ______cnsr2010/ • IEEE ISGT 2010 - 2010 IEEE Innova- posium/_____ tive Smart Grid Technologies Confer- z IEEE ICC 2010 - IEEE Int’l. ence, 19-21 June • EW 2010 – European Wireless 2010, Conference on Communications, Gaithersburg, MD. 12–15 April 23-27 May Lucca, Italy. Info: http://www.european- ______Capetown, South Africa. Info: z IEEE SECON 2010 - 2010 IEEE wireless2010.org ______http://www.ieee-icc.org/2010/ Communications Society Confer- • IEEE RFID 2010 - IEEE Int’l. Confer- ence on Sensor, Mesh and Ad Hoc ence on RFID 2010, 14-15 April J U N E Communications and Networks, 21- Orlando, FL. Info: http://www.ieee-rfid.org/ 25 June Boston, MA. Info: http://www.ieee-secon.org/ ___2010 • NGI 2010 - 6th Euro-NF Conference 2010/index.html on Next Generation Internet, 2-4 June ______IEEE WCNC 2010 - IEEE Wireless z Paris, France, Info: http://euronf.enst.fr/ Communications and Networking • Med-Hoc-Net 2010 - 9th IFIP Annual NGI2010/Home.html Conference, 18-21 April ______Mediterranean Ad Hoc Networking Workshop, 21-25 June Sydney, Australia. Info: ______http://www.ieee- • CTTE 2010 - 9th Conference of Juan Les Pins, France. Info: http://www.med- wcnc.org/______Telecommunication, Media and Inter- ______hoc-net-2010.org/ z IEEE/IFIP NOMS 2010 – IEEE/IFIP net Techno-Economics, 7-9 May Ghent, Belgium. Info: http://www.ctte-con- Network Operations and Manage- ______z ISCC 2010 - IEEE Symposium on ment Symposium, 19–23 April ference.org/______Computers and Communications, Osaka, Japan. 22-25 June z IEEE CQR 2010 - 2010 Int’l. Com- Riccione, Italy. Info: http://www.ieee-iscc.org/ • WTS 2010 - Wireless Telecommuni- munications Quality and Reliability ___2010 cations Symposium 2010, 21-23 April Workshop, 8-10 June Tampa, FL. Info: http://www.csupomona.edu/ Vancouver, BC, Canada. Info: J U L Y ___wtsi http://www.ieee-cqr.org/ • NOC/OC&I 2010 - 15th European M A Y z IEEE HEALTHCOM 2010 - IEEE Conference on Networks and Optical 12th Int’l. Conference on e-Health Communications & 5th Conference on Networking, Application & Services, • WCS 2010 - First Worldwide Optical Cabling and Infrastructure, 8- 1-3 July Cybersecurity Summit, 4-5 May 10 June Lyon, France. Info: ______http://www.ieee-healthcom.org/_____

z Communications Society portfolio events are indicated with a diamond before the listing; • SPECTS 2010 - 2010 Int’l. Sympo- • Communications Society technically co-sponsored conferences are indicated with a bullet sium on Performance Evaluation of before the listing. Individuals with information about upcoming conferences, calls for papers, meeting Computer and Telecommunication announcements, and meeting reports should send this information to: IEEE Communications Systems, 11-14 July Society, 3 Park Avenue, 17th Floor, New York, NY 10016; e-mail: [email protected];______fax: Ottawa, Canada. Info: http://atc.udg.edu/ +1-212-705-8999. Items submitted for publication will be included on a space-available basis. ______SPECTS2010

14 IEEE Communications Magazine • April 2010

______

ADVANCED OPTICAL FORMATS OF 40/100G AND BEYOND

Coherent detection and advanced signal processing are required for the test and measurement of advanced modulation formats that are currently realized for optical FREE ACCESS transmission of 40/100G and beyond. In this presentation the FOR A LIMITED TIME ONLY basic hardware building blocks and the necessary algorithms are introduced. New tools to characterize and quantify the UNTIL MAY 31 signal quality are applied to a number of exemplary signals.

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For other sponsor opportunities, please contact Eric Levine, Associate Publisher Phone: 212-705-8920, E-mail: [email protected]

NEW PRODUCTS

AGILENT TECHNOLOGIES’ NEW LTE translate into savings for both design handsets, basestations, wireless PC APPLICATIONS TARGET 4G effort and component cost. cards, and a host of other embedded SYSTEM-LEVEL DESIGNERS The W1910 LTE Baseband Verifica- solutions. tion Library reference blockset has The portfolio includes the industry's Agilent Technologies been updated to LTE v.8.9.0 and now first LTE front-end modules for Bands Agilent Technologies Inc. has intro- includes expanded PRACH and HARQ I, IV, VII and VIII (the SKY77445, duced a new line of system-level design support. The HARQ simulation sup- SKY77455, SKY77456 and SKY77458) and verification products for 3GPP port uses a unique dynamic dataflow for worldwide applications, and the LTE physical layer (PHY) design. In simulation mode. This mode allows the industry's first power amplifier modules addition to its traditional test and mea- symbol rate to change dynamically over supporting LTE-FDD for North Ameri- surement products, Agilent now pro- the course of the simulation while ca (the SKY77449 and SKY77453). vides predictive products and retaining the timing and carrier infor- www.skyworksinc.com algorithmic references for the Sys- mation necessary for full RF effects, temVue platform that are consistent frequency-dependent phase noise, and HIGH-END R&S ZVA67 VECTOR with the LTE v.8.9.0 (December 2009) channel fading. NETWORK ANALYZER standard. The new line includes four www.agilent.com Rohde & Schwarz products that accelerate 4G deployment for LTE system architects, baseband SKYWORKS SUPPORTS CUSTOMERS’ The high-end R&S ZVA67 vector hardware designers, and RF equipment LTE PLATFORMS WITH LINE OF network analyzer from Rohde & by bringing new levels of realism into POWER AMPLIFIER AND FRONT-END Schwarz is now also available as a four- the architecture and modeling stages. port model. This is the first network While 4G networks promise dramat- MODULES analyzer on the market to feature four ic improvements in data throughput Skyworks Solutions, Inc. test ports for measurements up to 67 and spectral efficiency, the complexity GHz. Its high dynamic range (110 dB at of the evolving 3GPP LTE standard has Skyworks Solutions has announced 67 GHz) and output power (6 dBm at forced many system architects to recon- the company's extensive portfolio of 67 GHz) give the R&S ZVA67 the flex- sider their use of general-purpose long-term evolution (LTE) power ibility and performance required for toolsets. By cutting across a variety of amplifier and front-end modules is now characterizing components and modules domains (such as signal processing and supporting the M710 solution from ST- in the microwave and millimeter-wave mathematics, baseband hardware Ericsson, a world leader in wireless range. It allows users in research and design, RF/analog design and measure- semiconductors and platforms. development to determine the S param- ments), Agilent's new 4G products are eters of multiport devices quickly and able to provide system architects with with high precision. As an extra benefit, the focused application support for the analyzer’s four internal signal LTE v.8.9.0 that they demand. Agilent's sources reduce test system complexity 4G products streamline verification and and the number of instruments bring measurement-level realism into required, e.g. for measuring frequency- the creative process. The result is high- converting DUTs, because no external er-performance Layer 1 architectures signal generators are needed. and algorithms resulting in earlier The new R&S ZVA67, with its design maturity and the need for less unique architecture that includes four design margin. ports, four integrated signal sources and The four new products being intro- eight receivers, enables measurements duced by Agilent include: on multiport devices such as mixers, The W1715 MIMO Channel Builder LTE is emerging as the 4G standard couplers or balanced DUTs, with just is a simulation blockset for LTE archi- of choice worldwide for mobile broad- one instrument. With its high output tecture and receiver designers, based on band systems. These 4G systems are power of 6 dBm and wide power sweep the WINNER and WINNER-II fading expected to significantly boost network range of > 40 dB, the R&S ZVA67 is algorithms. By incorporating non-ideal throughput, improve spectral efficiency able to characterize the small- and MIMO antenna performance (e.g., and performance, reduce latency, sim- large-signal behavior of active compo- crosstalk and directionality), the W1715 plify roaming and further drive nents. goes beyond these standard propaga- economies of scale. According to Glob- Linear and nonlinear measurements tion models. It enables 2D far-field al Mobile Suppliers Association (GSA), can be carried out using a simple test data to be imported from antenna mea- LTE network commitments increased setup. This advantage becomes appar- surements or 3D EM simulations, 100 percent in the last eight months ent, for example, when measuring the S including Agilent EM PRO. with 51 networks in 24 countries world- parameters or intermodulation of mix- The W1716 Digital Pre-Distortion wide currently committed to LTE. All ers or amplifiers, or when measuring builder helps LTE system integrators, major handset OEMs, infrastructure the group delay and phase of up- or RF component designers, and baseband suppliers, and operators worldwide are downconverters. architects quickly transition from 3G to now committed to this technology with Offering a frequency range up to 67 4G by creating baseband signal process- multiple trials underway. GHz, the four-port R&S ZVA67 covers ing networks that improve the range of Skyworks’ family of LTE products, the band intended for the wireless analog power amplifiers and transceiver which includes four front-end modules transmission of multimedia data (wire- ICs, improve efficiency, and extend bat- in addition to two power amplifier mod- less HDMI). Additional applications tery life. The W1716 also quickly assess- ules, provide the most complete and can be found in the aerospace and es the suitability of existing 3G designs flexible set of options for manufacturers defense sectors. for 4G applications. Such capabilities developing and building 4G-enabled www.rohde-schwarz.com

16 IEEE Communications Magazine • April 2010

CALL FOR PAPERS 44th Annual Asilomar Conference on Signals, Systems, and Computers

Asilomar Hotel and Conference Grounds Pacific Grove, California November 7-10, 2010 www.asilomarssc.org

Authors are invited to submit papers before June 1st, 2010, in the following areas:

A. Communications Systems: 1. Error Control Coding, 9. Compressive Sensing, 10. Information Theoretic Signal Processing, 2. CDMA, 3. Modulation and Detection, 4. Performance Bounds, 11. Spectral Analysis 5. Synchronization, 6. Ultra Wideband, 7. OFDM / Multicarrier, 8. Wireless Communications, 9. Optical Communications, F. Biomedical Signal and Image Processing: 1. Medical Image 10. Cognitive SDR, 11. Adaptive Waveform Design Analysis, 2. Imaging Modalities, 3. Advances in Medical Imaging, 4. Biomedical Signal Processing, 5. Biomedical Applications, B. MIMO Communications and Signal Processing: 6. Bioinformatics, 7. Image Registration and Multi-modal Imaging, 1. Space-Time Coding and Decoding, 2. Channel Estimation and 8. Image Reconstruction, 9. Computer Aided Diagnosis, 10. Functional Equalization, 3. Multi-User and Multi-Access Methods, Imaging, 11. Visualization 4. Cooperative Diversity. G. Architecture and Implementation: 1. Programmable and C. Networks: 1. Transmission Techniques for Ad Hoc Reconfigurable Architectures, 2. SOC Architectures, 3. Low-power Networks, 2. Wireless Sensor Networks, 3. Network Information Methods, 4. Compilers and Tools, 5. Integrated Algorithm and Theory, 4. Optical Networks Architecture Implementation, 6. Computer Arithmetic, 7. Numerical Processing D. Adaptive Systems and Processing: 1. Adaptive Filtering, 2. Fast Algorithms for Adaptive Filtering, 3. Frequency-Domain H. Speech, Image and Video Processing: 1. Speech Processing, and Subband Adaptive Filtering, 4. Adaptive Blind Processing 2. Speech Coding, 3. Speech Recognition, 4. Narrowband / Wideband Speech and Audio Coding, 5. Document Processing, 6. Models for Signal E. Array Processing and Statistical Signal Processing: 1. and Image Processing, 7. Image and Video Coding, 8. Image and Video Array Processing and Beamforming, 2. Sonar and Acoustical Segmentation, 9. Image and Video Analysis, 10. Image / Video Security, Array Processing, 3. Radar Array Processing, 4. Remote Sensing, Retrieval and Watermarking, 11. Image and Video Enhancement / 5. Signal Separation, 6. Estimation and Detection, 7. Non- Filtering, 12. Biometrics and Security, 13. Wavelets Gaussian and Nonlinear Methods, 8. Identification,

Submissions should include a 50 to 100 word abstract and an extended summary (500 to 1000 words, plus figures). Submissions must include the title of the paper, each author's name and affiliation, and the technical area(s) in which the paper falls with number(s) from the above list. Check the conference website (www.asilomarssc.org) for specific information on the electronic submission process. Submissions will be accepted starting February 1, 2010. No more than FOUR submissions are allowed per contributor, as author or co-author. All submissions must be received by June 1st, 2010. Notifications of acceptance will be mailed by mid August 2010, and author information will be available on the conference website by late August 2010. Full papers will be due shortly after the conference and published in early 2011. All technical questions should be directed to the Technical Program Chair, Dr. Miloš Doroslovaþki, e-mail [email protected],or the General Chair, Dr. Linda DeBrunner, e-mail [email protected]. CONFERENCE COMMITTEE

General Chair: Linda DeBrunner, Florida State University Technical Program Chair: Miloš Doroslovaþki, The George Washington University Conference Coordinator: Monique P. Fargues, Naval Postgraduate School Publication Chair: Michael Matthews, ATK Mission Research Publicity Chair: Murali Tummala, Naval Postgraduate School Finance Chair: Frank Kragh, Naval Postgraduate School

The site for the 2010 Conference is at the Asilomar Conference Grounds, in Pacific Grove, CA. The grounds border the Pacific Ocean and are close to Monterey, Carmel, and the scenic Seventeen Mile Drive in Pebble Beach. The Conference is organized in cooperation with the Naval Postgraduate School, Monterey, CA, and ATK Mission Research, Monterey, CA. The IEEE Signal Processing Society is a technical co-sponsor of the conference.

______

G l o b a l

N e w s l e t t e r April 2010

Activities of the IEEE ComSoc Nanjing Chapter By Nan Liu, Yueming Cai, and Guangguo Bi, ComSoc Nanjing Chapter, China

The IEEE ComSoc Nanjing Chapter was founded on April 13, 2008. The opening ceremony was held in Nanjing, China. Over 35 Chapter members and over 40 guests attended the ceremony. After the inauguration, two keynote addresses, “Development of IEEE in China” and “New Rising Wireless Communications and Wireless Networks,” were given. In the afternoon the Executive Committee of the Chapter was founded and discussed activities in 2008. The Chapter Officers are Prof. Guangguo Bi of Southeast University as Chapter Chair; Profs. Jinlong Wang, Baoyu Zheng, Jinkang Zhu, and Aiping Huang from various universities serve as Chapter Vice-Chairs; Prof. Yueming Cai is Secretary; and Prof. Nan Liu serves as Secretary and Treasurer. The opening ceremony of WCSP 2009 in Nanjing, China. Since coming into existence, the ComSoc Nanjing Chapter has been very active in hosting and sponsoring various activi- ond talk, “Resource Allocation for Cellular/WLAN Integrated ties to serve its members. In 2008 we technically sponsored/co- Networks” by Prof. Weihua Zhuang, also from the University sponsored three conferences/workshops: the International of Waterloo, Canada, focused on ways to enhance multiser- Conference on Communications and Networking in China vice provisioning by taking advantage of the complementary (CHINACOM 2008, co-sponsored) was held in Hangzhou in cellular/WLAN integrated network strengths, and details of August, accepting 270 papers for an acceptance rate of 32.8 call assignment/reassignment strategies, admission control percent, with 121 IEEE members attending the conference; policies, and the impact of user mobility and data traffic vari- the Workshop on Cognitive Wireless Networks (sponsored), ability. Both lectures drew a great deal of interest, and more held in Nanjing in September, with around 140 attendees, than 170 faculty members and students with more than 30 more than 30 being Chapter members; and the Conference on IEEE members in attendance. The third talk, given by Prof. Communications and Signal Processing in China (CCSPC Jacob Gavan, titled “Concepts, Applications and Design of 2008, co-sponsored) held in October in Zhengzhou with High Altitude Platform Radio Relays,” expounded the feasi- around 150 attendees. bility, recent status, technical issues, and advantages of differ- In 2009 the ComSoc Nanjing Chapter was even more ent categories of HAPS for several applications. The talk active. In June 2009 the (technically co-sponsored) Confer- concluded with recent trends in HAPS design and develop- ence on Green Wireless Technology and Systems was held in ments. Around 50 faculty members and students, among Huangshan, China, with 115 attendees from many Chinese whom over 10 were IEEE members, attended the lecture and universities and industrial companies. The main topics includ- benefited from learning about HAPS. ed power-efficient and energy-saving wireless communications The highlight of the activities of the ComSoc Nanjing system design and engineering techniques, wireless access pro- Chapter in 2009 was technically sponsoring the 2009 Interna- tocols, services, software design, and wireless resource saving. tional Conference on Wireless Communications and Signal In August 2009 the (co-sponsored) 9th Asian Conference Processing (WCSP 2009) held in Nanjing, China, on Novem- on Quantum Information Science (AQIS ’09) was held in ber 13–15, which attracted much attention from both the aca- Nanjing with around 180 attendees. AQIS ’09 focused on demic and industrial fields. It received a total of 1023 quantum information science and technology, bridging quan- submissions from 32 countries and regions. All papers were tum physics, computer science, mathematics, and information rigorously and independently peer reviewed by the 104 TPC technologies. members and a large number of reviewers. The conference In September 2009 we hosted three excellent talks by finally accepted 366 high-quality papers from 23 countries and IEEE ComSoc Distinguished Lecturers. The first talk, regions, representing an acceptance ratio of 36 percent. “Resource Management for Multitier Wireless Networks,” Accepted papers were grouped into 24 sessions with two given by Prof. Xueming (Sherman) Shen from the University tracks, Wireless Communications and Signal Processing. A of Waterloo, Canada, discussed issues on resource and mobili- highlight of the conference was the seven keynote speeches ty management algorithms, and achieving flexible and effec- delivered by distinguished scientific experts from all around tive utilization of network resources with guarantees for the world. About 300 researchers, scientists, engineers, and end-to-end QoS requirements of multimedia traffic. The sec- (Continued on Newsletter page 4)

Global Communications Newsletter • April 2010 1

White Spaces: Unused TV Band Channels for Rural Broadband in the United States By Ana Vazquez Alejos, Felipe Gil Castiñeira, Manuel Garcia Sanchez, and Iñigo Cuiñas University of Vigo, Spain; New Mexico State University, USA

During the next few years there are three technologies called to change together the traditional rigid policy for spectrum allocation: software defined radio (SDR), cognitive radio (CR), and white space devices (WDs). The CR paradigm proposes the creation of intelligent devices (usually developed with SDR platforms so that they can modify the radio parameters by software) which automatically change their conditions of operation in response to user demands or changes in the surrounding network. The application of these technologies in the channels reserved as guard bands, known as white spaces, is derived in WDs, which have made possible not only the use of the unused bands, but also the use of licensed bands by unlicensed users without causing interference to the legitimate owners. However, in some cases spectrum-sensing technology may not be completely effective in preventing co- or adjacent- Figure 1. White space channels available in December 2009 [4]. channel interference with the licensed user. In order to solve this problem, WDs have been coupled with geolocation tech- guards. Since the FCC announced the free use of part of the nology (e.g., GPS positioning along with a database of services unused broadcast channels in 2008, the technological commu- and operation times). In November 2009 the U.S. Federal nity has put forth a giant effort to satisfy all the parts involved. Communications Commission (FCC) launched a call for pro- The main opposition derived from the TV broadcasters that posals to manage a database network that registers and con- predicted important malfunctions and interference in their trols the use of an important amount of liberated spectrum licensed frequencies due to the WDs. A pilot developed in allocated in the 50–3000 MHz band to prevent the emerging 2008 demystified the prognosticated problems of co- and adja- new WDs from interfering with TV stations and other wireless cent-channel interference, showing that cognitive technologies services operating in this frequency region. are the answer for future services and gadgets operating in But is there available space in so large and attractive a white space gaps [2]. region of the extremely scarce frequency spectrum? The reali- Among the technical advantages offered by these gaps allo- ty is that a non-negligible number of gaps exist between cated under 900 MHz, despite their unlicensed status, we can 50–3000 MHz since the analog TV switchoff process started, mention the longer coverage areas that can be achieved (up to and this opportunity did not pass unappreciated by many eyes one mile), the reduced loss by penetration into buildings and (Fig. 1). The Wireless Innovation Alliance [1], formed by vegetation (a detail especially relevant in rural areas), and the companies such as Google, Dell, Hewlett-Packard, Motorola, reduced impact of multipath, at least compared to frequencies and Microsoft, became the impelling motor for the free use of of the 2.4 and 3.5 GHz bands. The availability of low-cost this accessible spectrum to develop a new generation of wire- hardware is not less important, due to the facilities for the less devices that could be the answer to the need for providing semiconductor technology at ultra high frequency (UHF). broadband access to U.S. rural areas in a cost-effective man- Nevertheless, not all the news is good. We cannot forget that ner. The first pilot was run in October 2009 in Claudville, Vir- longer antennas are required, and this fact can represent a busi- ginia [2]. ness opportunity for antenna manufacturers. Another downside There are several standardization organizations working on could be the need for incorporating geolocation in the WDs, white space technology. The IEEE [3] formed a work group increasing power consumption and size. that is closing the P1900 standard, which will try to provide In the future, the WDs and unlicensed services operating guarantees for compatibility and interference avoidance. Even in the unused broadcast frequencies will operate under the the WiMAX Forum has announced a modification to accom- guidelines given by CFR 47 Part 15 and amendments, retain- modate its technology to the white spaces in an attempt to ing the 6 MHz channel. More spectrum space is available in avoid losing the train of a business estimated in hundreds of the upper 700 MHz segment, which is expected to be assigned billions of dollars. to deploy a nationwide communication network for public The unused TV broadcast channels were liberated as a safety forces. This space contains 10 MHz blocks. result of the evolution toward digital terrestrial television The creation of the database proposed by the FCC will pre- (DTT) presenting blocks of 6 MHz, although this assignment vent licensed services, such as wireless microphone users or TV varies all over the territory. The origin of the changes in the broadcasters, suffering interference during their operation. The spectrum scene began with the abandonment of channels 52 standards under development will ensure that the new devices to 69, or 698–806 MHz, by broadcasters as a response to the have dynamic access control, taking into account the local spec- analog switchoff. This portion constitutes the 700 MHz spectrum conditions to modify transmission/reception. The database trum publically auctioned in 2008 to 100 bidders that obtained to be implemented plays an important role. about 1100 licenses for $20 million. These licensed spaces will 2010 can present the definitive and successful launch of provide mainly cellular expansion, including fourth-generation WhiteFi (a Wi-Fi style system operating in white spaces), thus Long Term Evolution (4G LTE), commercial mobile TV, and providing full access to the information society for rural areas. wireless broadband. The assignment of frequencies to DTT stations was done References in the space 54–698 MHz, channels 2–51, and due to the local [1] The Wireless Innovation Alliance [2] Bridge Wave Inc feature of these new assigned frequencies many gaps can be [3] www.ieee802.org/22 found in this region of the spectrum, mainly due to channel [4] http://www.showmywhitespace.com

2 Global Communications Newsletter • April 2010

Hightlights of the IEEE 9th TELSIKS Conference By Prof. Bratislav Milovanovic, University of Nis, Serbia

On October 7–9, 2009 the Faculty of Electronic Engineer- ing in Nis, Serbia, hosted fir the ninth time the biennial Inter- national Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services (TELSIKS 2009). Like the previous conference, TELSIKS 2007, this year’s event was organized jointly by the Faculty of Electronic Engi- neering Nis and the National Society for Microwave Tech- nique and Technologies. TELSIKS 2009 was organized under the technical co-sponsorship of the IEEE MTT Society, IEEE AP Society, and IEEE Region 8, and in cooperation with the IEEE Section of Serbia and Montenegro, IEEE MTT-S Chapter, and IEEE Communications Society Chapter of Ser- bia and Montenegro, as well as the National Society for Telecommunications and Society for ETRAN. The conference was also supported by the Serbian Academy of Science and Prof. A. Marincic opening the TELSIKS 2009 Conference. From Art, Academy of Engineering Science of Serbia and Montene- left: Chairmen Prof. K. Rao, Prof. B. Milovanovic, Prof. S. gro, Ministry of Science and Technological Development, and Tomacic, Prof. G. Stoyanov, and Prof. O. Fratu. Ministry of Telecommunications and Information Society. The main part of the conference program included presen- (IEEE CPP). All of the conference papers will be indexed in tations of scientific papers from a range of topics in the field the IET INSPEC database. of telecommunications. The review of submitted papers was Like previous TELSIKS conferences, this year’s conference done by an international board of conference reviewers, and was not just a conference with presentations of scientific the final selection was made by the Conference Program papers and exchange of experience, but also an event includ- Committee. The total number of papers selected for presen- ing many activities and meetings covering different important tation was 124, 19 of which were invited. Authors of the issues related to the field of telecommunications. The first of papers are scientists from the following countries: Bosnia and the additional activities was the Workshop “Trends in Multi- Herzegovina, Bulgaria, Canada, Czech Republic, Croatia, media Communications.” The lecturers were Prof. Kamisetty Germany, Greece, Italy, Libya, Macedonia, the Netherlands, R. Rao, University of Texas at Arlington, who gave a plenary Romania, Slovenia, Serbia, Ukraine, Spain, the United King- talk at the beginning of the Conference as well, and Prof. dom, and the United States. There were 11 regular sessions Zoran Bojkovic, University of Belgrade, Serbia. Then there and five poster sessions. All papers scheduled for presentation were two roundtables organized during the conference: “Strat- were published prior to the conference. The two-volume pro- egy of Scientific and Technological Development in tbe ceedings, accompanied by a CD-ROM, were distributed to all Republic of Serbia 2009–2014” and “Accreditation in Higher registered participants. It is important to note that the Confer- Education — Results and Forthcoming Activities.” Since actu- ence Proceedings, as an official IEEE publication, will be dis- al Serbian topics were considered, both roundtables were held tributed by the IEEE Conference Publications Program (Continued on Newsletter page 4)

The Spanish ICT Hyper-Sector Reduces Its Activity by Seven Percent By Juan Pedro Muñoz-Gea and Josemaría Malgosa-Sanahuja Polytechnic University of Cartagena, Spain

The Spanish Association of Electronics, Information Tech- fall is associated with a decline (for the first time in Spain) in nologies and Telecommunications (AETIC) has presented the the turnover of operators, a reduction in demand for fixed data of the ICT hyper-sector (telecommunications industries, networks, and stagnation of the fixed broadband market. In telecommunications services, information technologies, con- the second quarter computers and networks fell by 40 percent, sumer electronics, electronic components, and professional while mobile terminals fell 17 percent in the first six months electronics) relating to the period between July 2008 and June of 2009. 2009, which shows a reduction of 7 percent in activity. This The consumer electronics sector underwent the second figure shows an abrupt change of trend in the ICT sector, biggest decline, with a reduction in turnover of 22 percent which has always starred in annual increments upward, except (–27 percent, second quarter). The main causes are focused in 2008, when zero growth was recorded. on the falling prices of TVs — around 25 percent — and a All sectors that make up the hyper-sector have recorded reduction of close to 10 percent of sold units in the market. losses for the first time, highlighting the addition to this nega- The electronic components sector reduced its activity by 17 tive trend of the telecommunications services and information percent due to negative performance in other sectors. During technologies sectors (–4 and –2 percent, respectively). In addi- the second quarter, the trend worsened to –38 percent. The tion, the second quarter of 2009 showed a rapid decline of 13 professional electronics sector fell 8 percent, while from April percent in the hyper-sector (compared to the same period in to June 2009 the decline was more pronounced (–15%) 2008) with rates ranging from –8 percent in telecommuni- because companies had exhausted the sector’s backlog, and cations services to –38 percent in electronic components. replacement was very limited. The telecommunication industries sector registered the The telecommunications services sector decreased (for the biggest fall of the hyper-sector from July 2008 to June 2009 first time in history) 4 percent in billing. The second quarter (–25 percent), which accelerated in the second quarter of 2009 figures went down four more points(–8%). All components with a decline of 31 percent. Among other factors, this sharp (Continued on Newsletter page 4)

Global Communications Newsletter • April 2010 3

TELSIKS CONFERENCE/continued from page 3 dinner was organized at the end of the second day. Serbian national cuisine, an orchestra performing Serbian and interna- in Serbian. Both of them gained the attention of the Serbian tional music, and, most important, cheerful guests made the academic community. evening memorable. Since TELSIKS is dedicated to the introduction of new After the successful series of previous TELSIKS confer- telecommunications technologies and services, experimental ences, TELSIKS 2009 again offered a forum for promoting, broadcasting of digital television programs in Nis was set up discussing, and spreading ideas in the field of telecommuni- during the Conference, in cooperation with the national cations. telecommunication company Telekom Srbija, as well as three I would like to thank to all of the authors, members of the television companies, one of which has national coverage. TPC and organizing committee, reviewers, sponsors, In addition to the activities related to the presentation of exhibitors, and all the others who participated in organization scientific and professional results and activities, there were and in the conference itself. several commercial presentations. Some of the leading information and communications technology (ICT) companies presented their latest solutions and products. Furthermore, there SPANISH ICT HYPER-SECTOR/continued from page 3 was a one-day exhibition of IET journals. As a special attrac- tion, the presentation of the project “Computer Simulation showed negative trends in income (fixed, mobile, pay TV, and 3-D Modeling of the Original Patents of Nikola Tesla” wholesale services), except for Internet access, which had a was held. It was organized by the Faculty of Electronic Engi- positive but declining rate. This situation is a direct result of neering of Nis and the Nikola Tesla Museum in Belgrade. the combined effect of the fall in traffic and average revenue Among the other activities, there were meetings of the per line and per minute, in both fixed and mobile telephony. Executive Committee of the IEEE Section of Serbia and Mon- Despite all of this, mobile line and Internet penetration grew tenegro, and the IEEE Women in Engineering Chapter of moderately, and fixed access penetration was steady. Serbia and Montenegro. Furthermore, a meeting of the Ser- The information technologies sector has decreased by 2 bian Society of Cable Operators’ representatives was held as percent in turnovers during the past 12 months (–15 percent well. second quarter). The negative behavior of the software and The conference program was rich in social events as well. computer services has added to the behavior registered by There was a reception for invited authors organized by the hardware equipment for a long time. This is due primarily to Mayor of the City of Nis, followed by a nice musical perfor- decreased investment in professional systems, both public and mance for all conference participants. A sightseeing tour for private. all interested participants was organized. The conference gala

NANJING CHAPTER/continued from page 1 G l o b a l scholarship students from all over the world, about half of them IEEE members, participated in the conference. WCSP 2009 was very successful, and conference attendees felt that the conference provided them with a platform where they N e w s l e t t e r could learn about new advances in the wireless communica- www.comsoc.org/pubs/gcn tions and signal processing fields, and meet and discuss issues STEFANO BREGNI in research with peers working in the same area. They also Editor expressed that they look forward to participating in WCSP next year. Politecnico di Milano - Dept. of Electronics and Information Piazza Leonardo da Vinci 32, 20133 MILANO MI, Italy Ph.: +39-02-2399.3503 - Fax: +39-02-2399.3413 Email: [email protected],[email protected]

IEEE COMMUNICATIONS SOCIETY KHALED B. LETAIEF, VICE-PRESIDENT CONFERENCES SERGIO BENEDETTO, VICE-PRESIDENT MEMBER RELATIONS JOSÉ-DAVID CELY, DIRECTOR OF LA REGION GABE JAKOBSON, DIRECTOR OF NA REGION TARIQ DURRANI, DIRECTOR OF EAME REGION ZHISHENG NIU, DIRECTOR OF AP REGION ROBERTO SARACCO, DIRECTOR OF SISTER AND RELATED SOCIETIES

REGIONAL CORRESPONDENTS WHO CONTRIBUTED TO THIS ISSUE

MILAN JANKOVIC, SERBIA ([email protected]) JOSÉ MARIA MALGOSA-SANAHUJA, SPAIN ([email protected]) EWELL TAN, SINGAPORE ([email protected])

A publication of the ®IEEE Communications Society

4 Global Communications Newsletter • April 2010

October 4-6, National Institute of Standards and Technology www.ieee-smartgridcomm.org

1st IEEE International Conference on Smart Grid Communications October 4 – 6, 2010 ~ National Institute of Standards and Technology (NIST) Gaithersburg, Maryland, USA

Developing the Smart Grid has become an urgent global priority as its economic, environmental, and societal benefit will be enjoyed by generations to come. Information and communications technologies are at the core of the Smart Grid vision as they will empower today’s power grid with the capability of supporting two-way energy and information flow, isolating and restoring power outages more quickly, facilitating the integration of renewable energy sources into the grid and empowering the consumer with tools for optimizing their energy consumption. The 1st IEEE International Conference on Smart Grid Communications (SmartGridComm) is centered on all communications aspects that are relevant to the Smart Grid and aims at bringing together researchers from Academia, Industry, and National Labs to exchange novel ideas, explore enabling technologies, discuss innovative designs, and share field trial experiences and lessons learnt. The IEEE SmartGridComm Conference will be constituted of twelve Symposia. Each symposium will address a particular aspect of Smart Grid Communications. Prospective authors are invited to submit original contributions (standard two-column IEEE format and up to 6 pages) on all aspects of Smart Grid Communications to one of the following Symposia:

Paper Submission Deadline: May 1, 2010 Notification of Acceptance: July 19, 2010 Camera Ready Paper Due: Aug. 1, 2010 Author Registration Deadline: Aug. 1, 2010

George Arnold, NIST, USA Fred Baker, Cisco, USA Stefano Galli, Panasonic R&D, USA Hamid Gharavi, NIST, USA Simon Haykin, McMaster University, Canada www.ieee-smartgridcomm.org

SERIES EDITORIAL

DESIGN AND IMPLEMENTATIONS SERIES V: IMS APPLICATIONS AND SUPPORT

Sean Moore

he IEEE Communications Magazine editorial team char- legacy softswitches, which in practice were accessible only by T acterizes Series and Feature Topics as covering either telephony experts of the operating companies, an IMS-based vertical or horizontal topics. A topic is vertical if it is focused implementation is truly an open architecture that is accessible on a particular communication technology (e.g., next-genera- by the large community of Java enterprise application and tion optical switching). A topic is horizontal if it focuses on Java web application developers. The IMS framework con- some operational aspect that is common across many commu- verges telephony applications and enterprise IT applications nications technologies, such as interoperability testing or per- by providing a gateway (in the form of the SIP IMS service formance testing. The Design and Implementation (D&I) control [ISC] interface) between the signaling protocols of Series is horizontal, as D&I articles are intended to teach telephony systems and those of IT systems. industry professionals about building next-generation commu- The possibilities for high-value converged IMS applications nications products and services, regardless of the specific tech- and services are seemingly endless. But IMS service providers nology area. and enterprise vendors may not have the R&D resources nec- Coincidentally, however, five of the six articles in this fifth essary to meet their customers’ demands for IMS technologies installment of the D&I Series discuss IP multimedia subsys- — particularly the need for Java enterprise applications — tem (IMS) technology or support for IMS business operations. and are therefore dependent on third parties to provide the These articles were submitted independently without a call or resources. These third parties in some cases may be the cus- solicitations for IMS-related topics. This coincidence indicates tomers themselves. IMS’s open architecture enables third- the market strength of IMS and suggests that IMS is in an party participation, but IMS service providers and vendors active stage of its R&D life cycle where the graph of R&D must assist in this process and compete for these third-party investment vs. time has a positive second derivative. Hence, resources by providing effective application development tools this installment of D&I has been verticalized around IMS and and educational materials to the third party markets. Current- may be used by Communications Society members as a ly, these market forces are quite strong, in direct correlation resource to improve the efficiency and quality of their IMS- with the increasing penetration of IMS, and have clearly fac- related projects. tored into the “coincidence” that so many of the D&I articles IMS is an architectural framework that uses Session Ini- in this issue are IMS-related. tiation Protocol (SIP) signaling to deliver multimedia ser- Sal Loreto and an Ericsson team contributed “IMS Service vices over IP infrastructure. IMS was developed by the Development API and Testbed,” which addresses a significant Third Generation Partnership Project (3GPP) standards obstacle to IMS application development for Java developers. organization specifically to support delivery of 3G mobile In a native IMS implementation, SIP is used for communica- services. The IMS framework is sufficiently flexible such tions between the SIP router and JEE A/S-hosted applica- that it is now being used as the basis for both service tions, which requires that the application be structured as a provider and enterprise solutions using both wireless and SIP servlet to handle and process SIP messages. The Java wired infrastructure. application developer must then work directly with the SIP At the core of an IMS implementation is intelligent SIP protocol instead of with a programmatic Java library, which is routing, which interconnects users, devices, services, and contrary to the expectations of the Java development commu- applications. The capability to rout a SIP message to multiple nity. This article discusses how to design and build a Java pro- applications, which are hosted by Java Enterprise Edition- grammatic interface that abstracts IMS application compliant application servers (JEE A/S), may be the most development away from the SIP protocol level. A similar strategic capability of IMS. For example, when a caller sends approach is used by other IMS vendors and for the same rea- a SIP INVITE message to a callee to create a session, the son: to make IMS application development highly accessible IMS SIP router routs the INVITE message through a chain of to enterprise Java developers. independent applications or services for, say, call screening, Alejandro Cadenas and Alejandro Sanchez-Esguevillas of billing, QoS assurance, presence, user location tracking, E911, Telefonica I+D, working with Belen Carro of the University contact center information, contextual services, sleep proxies, of Valladolid, describe a practical deployment of contextual or enterprise applications. These applications are hosted by a services used to intelligently route calls in an IMS implemen- JEE A/S. Thus, unlike the call signal processing interfaces of tation (“Deployment of Contextual Corporate Telco Ser-

24 IEEE Communications Magazine • April 2010

SERIES EDITORIAL

vices”). Context-aware routing factors the users’ context — accuracy of their methods, and discuss how their system sup- location, mobility mode, presence state, current role, and so ports the new business and management processes of Korea on — into call routing decisions. In the enterprise setting, Telecom. context-aware routing may be used, for example, to route a Prasant Misra and a team from the University of New call to the current best contact device while selecting the most South Wales and the CSIRO ICT Centre share their experi- appropriate media (voice, voice mail, text, email, etc.) for the ence with designing and building communication systems that communication. In the consumer setting, context-aware rout- may be deployed, for example, in disaster-response situations, ing may be used to satisfy immediate consumer needs; for urban war zones, and other high-stress environments (“Safety instance, a subscriber desiring to exchange currency may be Assurance and Rescue Communications in High-Stress Envi- routed to the closest bank providing an exchange service. The ronments”). Real-world testing of communications systems in authors show how to architect context services in the IMS such environments is obviously a barrier, but underground framework to maximize the efficiency and effectiveness of mines display many of the extreme communications character- context-aware routing. istics of high-stress environments and may proxy for them as a The demand for contextual services drives a correlated design and implementation testbed. Solving the underground demand for sensor networks to collect context data. In a mine communications problem is by itself a significant contri- serendipitous complement to the article by Cardenas et al., bution, but such solutions may be leveraged into other high- May El Barachi and a team from Concordia University and stress environments. Misra et al. provide a tutorial on extreme United Arab Emirates University describe how to integrate communications characteristics and how they may be IMS implementations with wireless sensor networks (WSNs) addressed, discuss current solutions for communications in for collecting contextual data (“Architectural Components for mines, and conclude with an experiment assessing the perfor- the Integration of IMS and WSN”). The design and imple- mance of a wireless sensor network in an underground mine. mentation includes a WSN/IMS gateway and an extended I hope you both enjoy and learn from this fifth installment presence service for managing contextual information. Barachi of D&I as much as I did in serving as its editor. If these arti- et al. prove out their solutions by creating IMS applications cles and past installments of D&I have inspired you to consid- that use the contextual information collected from the WSNs. er contributing your valuable D&I knowledge to the Any commercial success of IMS may be attributed in part Communications Society’s members, contact me directly to technology benefits, but the majority share of the credit ([email protected])______so that together we can create a first- should be given to the business operations. Without efficient rate publication for the benefit of our industry members. The marketing, planning, delivery, and operational support for D&I Series Call for Papers may be found at ______http://www.com- IMS services, IMS service businesses may not succeed. The soc.org/livepubs/ci1/info/cfp/cfpcommagdesignimplementa-______next two articles provide valuable information that will help tion1.htm.______improve the chances for success. Please join me in acknowledging everyone that made possi- Often, communications services initiatives, such as an IMS ble this installment of the D&I Series: the authors’ sponsoring services rollout, are launched with (often unfounded) goals to organizations for donating their time, Avaya for donating my achieve some percentage of market penetration, such as “near time, the Editor-in-Chief Steve Gorshe, Joe Milizzo and Jen- 100 percent!” Is there a simple, low-cost method for estimat- nifer Porcello and her team at IEEE Communications Maga- ing realistic goals? Or equivalently, is there a method to esti- zine, and the many anonymous reviewers who ensured the mate if the current business environment supports the quality of the articles. attainment of such goals, or are additional stimuli needed? Ryszard Struzak, IEEE Life Fellow, proposes such a method BIOGRAPHY in “Broadband Internet in EU Countries: Limits to Growth.” SEAN MOORE [M’01, SM’03] ([email protected])______has over 25 years of Struzak borrows the logistic growth function used in biological experience in a variety of technology industries, and has been working in system modeling and applies it to early data from the Euro- networking and telecommunications since 2001. He currently works at pean i2010 broadband initiative, which has a goal of 90 per- Avaya, a vendor of enterprise communications solutions, where he has cent broadband penetration for each member country of the served as chief scientist in the gateways division, as an enterprise architect in the CTO office, and currently serves as the chief architect for developer European Union. Given current conditions, Struzak’s method platforms and as Avaya's representative to ECMA International. One of his shows that many countries are not on a trajectory to achieve current projects is architecting the software development kits (SDKs) and the goal, which suggests that actions be taken to change the platforms for use by third-party developers to create enterprise telephony business environment and thereby improve the likelihood that web applications and SIP/IMS applications. In the past he was chief scientist at Cetacean Networks, a vendor of advanced routers and routing appli- the i2010 goals will be met. Struzak’s method is quite general, cations, senior director of R&D at MadeToOrder.com, a developer of and its application to analysis of IMS service penetration supply-chain management e-commerce solutions, and director of advanced goals should be straightforward. systems and director of business development at BBN Corporation, an R&D IMS not only drives more and richer IP multimedia ser- services provider to the U.S. Department of Defense. He has made contributions in peer-to-peer media distribution protocols, network admission vices but also drives growth of organizations that provide IP control, web-telephony convergence, network tomography, digital signal multimedia services over third-party IP network infrastructure. processing, fast Fourier transform (FFT) algorithms, medical imaging, global The network operators therefore need to measure precisely climate modeling, global-scale distributed databases, global-scale logistics the traffic volumes of individual media services for accurate and scheduling systems, e-commerce, genetic algorithms, automated hardware design, queuing theory, TCP technology, and scheduling theory. His cost accounting and charging. Operators must also measure software for FFTs on the 2-sphere is open-sourced as SpharmonicKit. He traffic to ensure QoS agreements, and to use the data in net- also serves as the Design and Implementation Series Editor and Associate work design and planning. JungYul Choi and a team from Editor-in-Chief for IEEE Communications Magazine. He is a charter member Korea Telecom built a service traffic management system to of the IEEE Standards Activities Board. He received a B.S. degree in electri- solve these problems. In “Service Traffic Management System cal engineering from Tulane University in 1983, an M.S. in mathematics from the University of New Orleans in 1990 (SIAM Applied Mathematics for Multiservice IP Networks,” Choi et al. share their experi- Award co-recipient), and M.S. and Ph.D. degrees in computer science from ence and lessons learned on the project, prove empirically the Dartmouth College in 1993 and 1994, respectively.

IEEE Communications Magazine • April 2010 25

TOPICS IN DESIGN &IMPLEMENTATION IMS Service Development API and Testbed

Salvatore Loreto, Tomas Mecklin, Miljenko Opsenica, and Heidi-Maria Rissanen, Ericsson Research

ABSTRACT service to which the user is subscribed). As logical elements IMS architecture defines different The IP multimedia subsystem defined by the call session control functions (CSCFs), which are Third Generation Partnership Project is the essentially SIP proxy servers supporting IMS architecture merging the Internet and telecom specific mechanisms. The serving CSCF (S- worlds. The IMS was designed to make it easy CSCF) is the central node of the signaling plane. for third-party developers to make their applica- It is essentially a SIP server, but also performs tions available to all IMS users, and by doing so session control. It also acts as a SIP registrar, provide more than only the basic telecom ser- maintaining a binding between the user’s loca- vices like voice, messaging, presence and contact tion and the user’s SIP address of record. All the management. However, good knowledge of the SIP signaling that is sent or received by the IMS IMS network architecture and the underlying terminal traverses the allocated S-CSCF. The S- Internet protocols is still needed to develop IMS CSCF inspects every SIP message and deter- applications. In addition, telecom expertise is mines whether the SIP signaling should visit one needed to deploy the application and provision or more application servers (ASs) en route users. To ease the development and deployment toward the final destination using the informa- process, it is essential to provide application tion contained in the initial filter criteria (IFC). developers with APIs and similar tools available This is illustrated in Fig. 1. for Web 2.0 application development today. In An AS is a logical IMS element that hosts, this article we explore the architectural and pro- executes, and provides the business logic for tocol aspects that enable third-party IMS appli- end-user services. The AS can be located either cation development and deployment. We also in the home network or in an external third- study how the applications will coexist with other party network with which the home operator applications already deployed in the IMS. More- maintains a service agreement. Thus, unlike IP over, we describe Java libraries exploiting the networks, an IMS network does not respect the functionality of the IMS both in the terminal end-to-end Internet philosophy which mandates client and within the core network. We also that all the intelligence is at the edges of the show how these Java libraries can be used for network. Instead, an IMS network allows part of developing and deploying new applications in an the intelligence of a service to be hosted inside IMS testbed, which provides IMS functionality the network (i.e., in the AS). This way, terminals over commercial 3G networks. with limited capabilities can access complex services using the support from the network. INTRODUCTION The IMS architecture was designed to be flexible and expandable, allowing third-party develop- The Third Generation Partnership Project ers to bring new services online. However, 3GPP (3GPP) developed the IP multimedia subsystem gave little attention to the issue of actually creat- (IMS) [1] architecture with the aim of providing ing and deploying services easily. As a conse- and handling a large variety of innovative ser- quence, exposed IMS interfaces have been vices. To achieve these goals the IMS uses Inter- complex and have not attracted developers. There- net Engineering Task Force (IETF) protocols. fore, the existing IMS services have been used just In particular, it uses Session Initiation Protocol like a set of operator controlled bit-pipe utilities. (SIP) [2] as the session control protocol to estab- During the last few years there have been lish and control multimedia sessions. several efforts to expose IMS functionality to IMS is a SIP-based network architecture that application developers via high-level interfaces. provides a multiservice environment with multi- However, in order to provide new services to media capabilities. For this reason, 3GPP has users of the IMS network, it is also necessary to introduced logical elements as well as protocol implement the business logic for the new ser- mechanisms that are not defined in the plain vices within the network. Until now there has IETF SIP. not been any effort to expose IMS network capa- The IMS network contains at least one home bilities to service developers via high-level inter- subscriber server (HSS), which is the central faces that would have allowed easy development repository for user-related information (e.g., the and deployment of new services to an AS.

To try to resolve this limitation we have published high-level Java IMS application program- AS AS AS ming interfaces (APIs) and an IMS testbed that enables application developers, with no prior knowledge about IMS or SIP, to build IMS applications and deploy the applications in a live ISC IMS network (http://labs.ericsson.com). The remainder of the article is organized as HSS S-CSCF follows. In the next section we explore the currently available Java APIs for both the terminal and server sides, discuss their functionality, and high- P-CSCF I-CSCF light the inconsistencies and disalignments between them. We then describe a presence service implementation built on top of the provided IMS API. We discuss application and service rout- Figure 1. SIP routing in IMS. ing in IMS. We show how the provided Java libraries can be used for deploying new applications in an IMS testbed, which provides the IMS functionality over commercial 3G networks. To be naling for Java EE applications. able to use the services of the testbed network, the SIP servlets are server-side components that user has to be provisioned to the network. This is perform SIP signaling. They are managed by a described later. In the final section we conclude SIP servlet container, which is usually part of a the article and propose some future work. SIP AS. The SIP Servlet API takes care of managing network listening points, retransmissions, ORE and SIP message headers such as CSeq and Call- IMS C API ID. The SIP Servlet 1.1 API also provides a Java Micro Edition (Java ME) is the most ubiqui- standardized way to develop converged applica- tous application platform for cellular phones with tions that use both SIP servlet components and constrained resources. To lower the barriers for standard Java EE components such as Enter- Java ME IMS application development, the Java prise Java Beans (EJBs). Community Process (JCP) defined an IMS Ser- For non-SIP experts to develop IMS applica- vices API package for the Java ME platform. This tions the abstraction level of the JSR 289 API is package is provided in Java Specification Request too low. Thus, a higher-level interface similar to (JSR) 281 (http://jcp.org/en/jsr/detail?id=281). To the terminal side’s JSR 281 is needed. To solve target the whole Java ME user community, JSR this inconsistency between client and server 281 was designed using the following design APIs, we implemented an IMS Core API for principles: Java EE. • High abstraction level of the API allows non-IMS developers to create IMS applica- IMS API LAYERS tions. The IMS core API for Java EE was designed to • Creating an IMS-aware application takes also provide on the server side a higher level of only a few steps. Thus, the developer can abstraction where the developer does not need concentrate on the logic of the application. to be aware of the SIP Servlet programming • The API allows access to low-level APIs for model or SIP signaling. As the SIP protocol is developers with IMS knowledge. On the asynchronous, communication initiated by lower level, for example, JSR 180 (http://jcp. remote endpoints is handled by attaching listen- org/en/jsr/detail?id=180), which is the SIP ers to the created services. Applications initially API for Java ME, can be used. need to create an ImsCoreService as a handle The IMS API defines a set of service meth- for creating new SIP transactions and receiving ods that can be used to build IMS applications: incoming transactions. A listener is attached to • Session represents media exchange the ImsCoreService to listen to remotely initiat- between two IMS endpoints. ed transactions such as session invitations. When • Capabilities instance queries a remote the application needs to initiate a transaction, endpoint about its capabilities. the specific service is created by using the • Reference is used for referring to a ImsCoreService. As with attaching a listener to remote endpoint of a third-party user or the ImsCoreService, a listener can also be service. attached to the specific service to receive mes- • Subscription subscribes to event state sages related to the service. Notifications about from a remote endpoint. delivery success are delivered using the listener • Publication publishes event state to a attached to the specific service. remote endpoint. One of the design requirements for the IMS • PageMessage is used for instant messages core API was to have a similar IMS API for or exchange of small amounts of content both Java ME and Java EE. To achieve this, we outside of a session. did alignments in the abstraction level, applica- No similar high-level IMS API has been tion, and service routing, and supported fea- defined on the server side for Java Enterprise tures. Full alignment is not possible due to the Edition (Java EE). For Java EE there is JSR differences between the Java platforms. The 289, which is the SIP Servlet API 1.1 (http://jcp. IMS API layers for both Java EE (server side) org/en/______jsr/detail?id=289). It standardizes the and Java ME (client side) are shown in Fig. 2. platform for delivering functionality for SIP sig- On top of the IMS core API, it is possible to

IEEE Communications Magazine • April 2010 27

Registration to the Server API layers Terminal API layers IMS network can be Application Application done both from the Application Application Application layer server and the client Application Application Application Application side. However, an application Conformance Gropu mgmt deployed on the Presence Messaging Presence AS is considered to IMS CoSe IMS CoSe be in a trusted domain without the need for registering the user of the Media IMS adaptation layer application. IMS Core API control (JSR 281) JSR309

JSR289 JSR180 Java EE (Sailfin application server) Java ME (client platform)

Figure 2. The IMS API layers.

build communication services (CoSes): a set of the SIP API for Java ME (http://jcp.org/en/jsr/ rules, procedures, and allowed media for a spe- ______detail?id=180). A JSR 180 stack, which was cific type of service. The most common CoSes implemented as part of the project, can be used are presence, messaging, and conferencing. if there is no native JSR 180 in the terminal. So Developers can build their applications using far we have used only Sony Ericsson phones to either the IMS core API or CoSe APIs, or both. test the APIs. Developers who are familiar with IMS and SIP concepts can also access lower-level APIs. IMS CORE API FUNCTIONALITY For brevity, this article does not provide The core API provides high-level interfaces that details of the CoSe services or APIs. can be accessed from both the CoSe and application layers. The level of abstraction is similar to Server Implementation — As shown in Fig. 2, the abstraction level used in JSR 281. New IMS on the server side there is a Sailfin AS at the services can be introduced by combining existing bottom as the deployment platform. Sailfin con- interfaces or adding new ones. Currently exposed tains a JSR 289 library. The server side IMS API functionality is described in the following. implementation is built on top of the JSR 289 API. The abstraction level and design philoso- Registration — To be able to use IMS func- phy of the server implementation are based on tionality, the user needs to be registered to the the JSR 281 API. IMS network. Registration is done by invoking In the server API we used service and call- the Registration interface method and by back methods similar to the ones used in the listening to the registration events. Registration JSR 281 API. The callback concept is based on to the IMS network can be done from both the the listener and observer design patterns server and client sides. However, an application (http://java.sun.com/developer/JDCTechTips/200 deployed on the AS is considered to be in a 6/tt0113.html).______Using the callback mechanism, a trusted domain without the need to register the user can set a listener for an invoked method to user of the application. receive corresponding events. The core API’s connections to the IMS net- SIP Session Management — The SIP session work are handled by JSR 289 and the Java plat- management interface provides the SIP core form. protocol functionality. By invoking interface methods and listening to the events, it is possible Terminal Implementation — On the terminal to perform all basic SIP session actions: invite a side, there is an implementation of the JSR 281 party to a session, accept and terminate a ses- API as shown in Fig. 2. In addition to that, we sion, and respond to requests. SIP signaling is implemented an IMS framework, which controls taken care of by the API implementation, but the connection to the IMS network. The IMS the user has to know how to manage concepts framework also takes care of routing the incom- such as an ImsSession and ImsMedia. ing requests to the correct application. The IMS framework can only be used in ter- Instant Messaging — The IMS core API sup- minals that have support for JSR 180, which is ports two modes of instant messaging: session

28 IEEE Communications Magazine • April 2010

The presence service Terminal Application server allows a user to be

Java ME MIDlet Java EE application informed whether or not other users are Application CoSe layer interfaces online and, if they CoSe layer Presence are online, whether Presence they are idle or busy,

IMS adaptation as well as other layer (JSR231) The core API layer details of their (JSR281 alike) communication JSR180 stack Service means and router capabilities. IMS interfaces

JSR180 Application stack router Client Java ME platform ServerSailfin platform (JSR289)

Device Network infrastructure infrastructure

Figure 3. Presence example of a CoSe service.

mode and page. be used to indicate if a user supports audio, Page messaging uses SIP MESSAGE, as video, or instant messaging. defined in [3]. Due to the size limitations of IMS Presence service is the first CoSe service we nodes like the session border controller (SBC), a provide to developers, which is built on top of bigger amount of content should preferably be the IMS core API in Java EE and on top of JSR sent using the session mode. 281 in Java ME. Examples of both a Java ME Session mode messaging supports exchanging MIDlet and a Java EE application using the arbitrarily sized content between users. In ses- presence service are shown in Fig. 3. sion mode the messaging service creates a ses- At the time of implementation, JCP had not sion with the destination and delivers the defined any presence API; thus, our implemen- messages using the Message Session Relay Pro- tation is not based on any JSR but follows Open tocol (MSRP) [4]. An MSRP session is set up by Mobile Alliance (OMA) application-level speci- exchanging certain information using SIP, such fications. The Presence API allows users to pub- as the MSRP uniform resource identifier (URI). lish presence information and subscribe to other users’ presence information. The API uses SIP Event Notification and Publication — The Extensible Markup Language (XML) Configura- event notification and publication interface pro- tion Access Protocol (XCAP) [7] for manipulat- vides methods for using SIP subscriptions, notifi- ing presence lists and presence authorization cations, and publications. SUBSCRIBE and rules on the XML Document Management Serv- NOTIFY functionality is implemented according to er (XDMS). Presence authorization rules define RFC 3265 [5] and PUBLISH according to RFC the authorizing policy for watchers. Mechanisms 3903 [6]. On top of this functionality, a CoSe ser- to create, modify, fetch, and delete XML docu- vice can, for example, publish a user’s presence ments are defined by OMA. To get real-time information or subscribe to other users’ presence updates about the changes in the XML docu- information. ments, users can subscribe to the different events by using SIP NOTIFY requests as defined in the SIP event notification framework [5]. SIP event PRESENCE SERVICE notification and publish functionality is used MPLEMENTATION from the IMS core API in Java EE and from the I JSR 281 API in Java ME. The presence service allows a user to be informed whether or not other users are online PPLICATION AND ERVICE OUTING and, if they are online, whether they are idle or A S R busy, as well as other details of their communi- As described earlier, IMS is an architecture able cation means and capabilities. Capabilities can to support several end-user services. The partic-

IEEE Communications Magazine • April 2010 29

ular service a user intends to use in a session has the application is done by the SR. The SR uses Once the chain of to be identified at the time the IMS session is the received tag to select the service within the applications is set for established so the S-CSCF can trigger the SIP application. If the requested service is identified, signaling to the particular AS providing the ser- the request is sent toward the service for further the initial request, vice. This is illustrated in Fig. 1. SIP messages processing. all subsequent have to carry a tag to allow the terminal and network to identify the service intended to be used APPLICATION ROUTING requests will be during an IMS session. A complete service, such as a pure SIP or con- routed to the The SIP Caller Preference mechanism (RFC verged service, can be built by combining several applications in the 3841) [8] describes a set of extensions to SIP applications hosted by an AS. Each individual that allow a caller to express its preferences application performs a part of the service inde- same order. about request handling in servers. These prefer- pendent of the others. The SIP container needs This way, complex ences include the ability to select to which URI to determine which application to invoke when a request gets routed, and make it possible to an initial request is received. This is done by an services can be built specify certain request handling directives in application router (AR), which implements the without making proxies and redirect servers. Three request head- SIPApplicationRouter interface defined in JSR individual er fields, which specify the caller’s preferences, 289. The AR is not a part of the container, but are specified: Accept-Contact, Reject-Contact, rather an extension thereof. applications and Request-Disposition. In particular, the The AR may use any algorithm or data source too complex. Accept-Contact header explicitly contains the to determine the order in which applications are desired properties of a terminal to which the invoked for an initial request. Once the chain of request is to be routed. 3GPP extends this applications is set for the initial request, all sub- mechanism to also convey the communication sequent requests will be routed to the applica- service identifier (ICSI) and the IMS application tions in the same order. This way, complex reference identifier (IARI) in the Accept-Con- services can be built without making individual tact header. applications too complex. The application inde- As the logic of each standardized IMS service pendence and composition used in JSR 289 is can be utilized by a number of different service adapted from the distributed feature composi- applications, each of which implements a partic- tion (DFC) architecture [9]. ular end-user service, both the ICSI and IARI Converged applications are identified by the tags are needed in the SIP Accept-Contact head- application name, defined either in the deploy- er in our API implementation. These tags are ment descriptor or as an annotation, as described needed to determine the correct IMS services later. When an application is deployed or unde- and to address the correct application. ployed, the AR is notified about the change in the available applications. At the start, the con- SERVICE ROUTING tainer notifies the AR about the available appli- As the IMS Core API supports the IMS multi- cations. The names of the affected applications service concept where several services are avail- are included in the notifications. able to the user, a service routing mechanism is needed in the IMS Core API. To route the APPLICATION ROUTER IMPLEMENTATION request to the correct service, we use the 3GPP In our AR implementation we use the feature ICSI feature tag in the SIP Accept-Contact tag defined in RFC 3840 [10] and RFC 3841 [8] header. For example, multimedia telephony ser- to map initial requests to the correct application. vice (MMTel) would be identified with the fol- We did not implement the required features for lowing ICSI tag: *;+g.3gpp.app ref = application composition in the AR, since only “urn:Aurn-xxx:3gppservice.ims.icsi. basic services were needed. mmtel”. When the container receives an initial request The ICSI tag is configured in the applica- of which it has no prior knowledge, it forwards tion deployment descriptor and registered in the request to the AR. The AR is not allowed to the deployment phase, described later. Two modify the request in any way, but it extracts the dependent tag components, ServiceID and Ser- required information from the request to be able viceName, are linked with a configured service to select the correct application. In our imple- and used in subsequent service routing. Provid- mentation we extract the Accept-Contact header ing a combination of ServiceID and Service- and analyze its content. The AR will extract the Name allows application developers to IARI value to select the application to which the instantiate the same IMS service with different request should be routed. The ICSI is not used configurations. by our AR implementation, but can be used by A service router (SR) is a core API compo- the SR, as described earlier. nent that handles routing logic on the server side. The IMS system is responsible for routing EPLOYMENT OF PPLICATIONS SIP signaling to the applications that are part of D A a service. Routing is based on the first request To deploy an application using the IMS APIs to sent to the S-CSCF. The request initiator inserts a real IMS network, the IMS testbed provided an ICSI tag into the Accept-Contact header and by Ericsson Labs can be used (http://developer. sends it toward the IMS network. The S-CSCF labs.ericsson.net/apis/mjcf). In this testbed the uses the IFC to identify the AS that has to be SIP servlet container is a Sailfin AS (https://sail-______included in the signaling path. After the request ______fin.dev.java.net). Sailfin is based on the Glass- is received at the AS container, the target appli- FishAS (https://glassfish.dev.java.net) with a SIP cation is selected using application routing, servlets technology extension. The network which is described later. Service selection within architecture of the testbed is shown in Fig. 4.

30 IEEE Communications Magazine • April 2010

The network contains an S-CSCF, HSS, SIPAS, and a presence server containing an XDMS. The Sailfin AS is located in another network that is XCAP connected to the IMS network with a virtual pri- SIP vate network (VPN) tunnel. An SBC manages Diameter Sailfin AS the signaling and MSRP streams to and from the HTTP/CAI3G LDAP terminals. There is also a provisioning server, which is discussed in the next section. To deploy an application to the IMS network, the application needs to be uploaded to the Sail- Internet fin AS. Deployment of IMS applications is simi- Provisioning lar to deployment of normal web applications. server SBC S-CSCF (EMA) Directories and files of an IMS application Terminal should be laid out according to the standard web application layout. A standard web application configuration file, Presence server HSS sun-web.xml, is needed to deploy the SIP appli- NAT/FW cation. If HTTP servlets are used, a web.xml deployment descriptor is also needed. In addition, the following SIP-specific configuration files are needed: • sip.xml is the SIP deployment descriptor. Figure 4. Ericsson Labs IMS network. It contains the name of the application and servlet mappings. It is similar to the standard web.xml file, but instead of a URL To contact the EMA provisioning system pattern used in web.xml, the header field of located in the Ericsson Laboratories IMS testbed a SIP request is used. network, we have implemented a provisioning • ims.xml is the IMS descriptor of the appli- application. This application is deployed on the cation. It is not part of the SIP servlet API, Sailfin AS in the testbed network. Data related but a descriptor needed by the IMS APIs. to the applications is stored on the AS, and data ims.xml contains the ID of the service, the related to the services of the IMS is stored on address of the CSCF and the SIP URI of the HSS. To make an initial provisioning request, the user on whose behalf the AS is per- a SOAP-based authorization request is sent from forming actions. the provisioning application to the provisioning As an example, we have an application named server. This request contains the mobile sub- com.imsinnovation.sendmessage, which scriber integrated services digital network is a simple application able to receive and send (ISDN; MSISDN) identifier of the user. page messages. The name of the application is If the response is successful, the user will defined in the sip.xml deployment descriptor: receive an SMS message with a provisioning password to the mobile phone. To finalize provisioning, a final request containing the password is sent from the application to the provisioning com.imsinnovation.sendmes- server. This final request creates the IFC, and sage provisions the user to the IMS network and its Page message test update the user profile and for example to provision new services. The corresponding IARI value to route initial request to this application is LESSONS LEARNED AND +g.3gpp.app_ref= ”urn:urn-xxx:3gpp-application. FUTURE WORK com.imsinnovation.sendmessage” The IMS vision is to create an ecosystem where all the applications provided by the developer ROVISIONING community are available for all users of the IMS. P As IMS networks are being installed in opera- Before the user can use the services of the IMS tors’ networks around the world, it seems essen- network, s/he needs to be provisioned to the net- tial to have APIs and tools available for IMS work. In our implementation we use the Erics- application developers similar to the tools avail- son Multi Activation (EMA) provisioning system able for web developers today. We address this (http://www.ericsson.com/solutions/page.asp?Arti problem by providing developers with high-level cleId=89A4A5D2-13F7-477C-9636-CB92______Java APIs exposing the functionality of the IMS FA37FD6F)______to provision users to the IMS net- network and a live IMS testbed network. work. EMA provides a provisioning interface The main objective of this project was to pub- called the Customer Administration Interface lish high-level Java EE and ME APIs that would Third Generation (CAI3G). CAI3G follows allow web application developers to include IMS industry standards and best practices, and it uses functionality in their applications. One of the Simple Object Access Protocol (SOAP) over requirements was that no prior knowledge about HTTP. An EMA system can be used indepen- IMS or SIP should be required of the develop- dent of the operator. ers. Thus far we have published a core API pro-

IEEE Communications Magazine • April 2010 31

viding the functionality described earlier. We For the sake of brevity, this article does not To efficiently use have also published a presence API, which is an provide details of the CoSe services or APIs; example of a CoSe service, for both Java EE and however, we intend to publish these details at a presence Java ME. future date. information, some As we are trying to merge the telecom and information about Internet worlds, we are dealing on one side with REFERENCES asynchronous network signaling and on the presence standards [1] 3GPP TS 23.228, “IP Multimedia Subsystem (IMS); Stage other with synchronous Internet signaling. One 2,” Sept. 2008. could be useful. of the biggest difficulties came from differences [2] J. Rosenberg et al., “SIP: Session Initiation Protocol,” between SIP and HTTP sessions. Although both IETF RFC 3261, June 2002. Defining good protocols use a request-response pattern and [3] B. Campbell et al., “Session Initiation Protocol (SIP) samples on how to Extension for Instant Messaging,” IETF RFC 3428, Dec. their syntaxes are similar, SIP is still an asyn- 2002. use these concepts chronous communications protocol. As commu- [4] B. Campbell, R. Mahy, and C. Jennings, “The Message nication systems are inherently stateful, state Session Relay Protocol (MSRP),” IETF RFC 4975, Sept. will help the and transaction management is arguably the 2007. [5] A. B. Roach, “Session Initiation Protocol (SIP) — Specific developers to build biggest shortcoming of the SIP servlet layer we Event Notification,” IETF RFC 3265, June 2002. have to consider. To balance the two different their own [6] A. Niemi, “Session Initiation Protocol (SIP) Extension for approaches, we introduced some level of state Event State Publication,” IETF RFC 3903, Oct. 2004. applications. information in between and used a callback [7] J. Rosenberg, “The Extensible Markup Language (XML) Configuration Access Protocol (XCAP),” IETF RFC 4825, mechanism dependent on network interactions. May 2007. For balancing on the Internet side we used [8] J. Rosenberg, H. Schulzrinne, and P. Kyzivat, “Caller Comet’s (http://docs.sun.com/app/docs/doc/ Preferences for the Session Initiation Protocol (SIP),” ______8204496/ghgxk?a=view) asynchronous, non- IETF RFC 3841), Aug. 2004. [9] M. Jackson and P. Zave, “Distributed Feature Composi- blocking HTTP mechanisms. tion: A Virtual Architecture for Telecommunications Ser- Another difficulty we faced during the project vices,” IEEE Trans. Software Eng., 1998. was local testing of IMS applications. Although [10] J. Rosenberg, H. Schulzrinne, and P. Kyzivat, “Indicat- we had an IMS environment for local testing, it ing User Agent Capabilities in the Session Initiation Pro- was not fully compliant with standards and tocol (SIP),” IETF RFC 3840, Aug. 2004. requirements used in the real testbed network. This meant it was not possible to test IMS net- BIOGRAPHIES work-dependent functions locally but in the SALVATORE LORETO [SM] received his degree in computer remote, real IMS network. Therefore, testing of engineering from the University of Napoli Federico II, Italy, functions like presence or provisioning was done in 1999. He obtained a Ph.D.degree in computer networks in 2006. Since 2000 he has been working for Ericsson, first in two steps. in Italy and now in Finland. He is currently working as a Most of the developers who have used the research scientist at Ericsson Research in Finland. He has APIs thus far have been students. The abstrac- authored and co-authored several papers on transport and tion level in the APIs is higher than SIP, and signaling protocols. His research interests include signaling, multimedia applications, transport protocols, and network that has been clear enough for most of the security. He is also an active member of the IETF and cur- developers. However, to efficiently use pres- rently co-chairs the HyBi wg. ence information, some information about presence standards could be useful. Defining TOMAS MECKLIN has been working for Ericsson since 1993 with various communication technologies. He graduated in good samples on how to use these concepts 1994 from the Computer Science Department of Tekniska will help the developers build their own appli- Lroverket i Helsingfors. Since 1999 he has been working as cations. an architect for a number of SIP-based call controllers for It is clear that providing only Java APIs is not IMS. Currently he is working as research scientist at Ericsson Research, Finland (Nomadiclab), with his main focus on ser- enough for the needs of the developers. Our vice enablers, multimedia applications, privacy, and security. current and future work is related to implementing interfaces other than Java. Currently, we are MILJENKO OPSENICA received his M.Sc. degree in electrical implementing APIs (e.g., for representational engineering and information technology from the Universi- ty of Zagreb — FER, Croatia, in 2001. He joined Ericsson in state ttransfer [REST]). Other interfaces such as 1998. He has been working on a number of signaling- .Net or SOAP need to be considered as well. In based call controllers. Currently he is working as a research addition, real-time media such as voice and scientist at Ericsson Research, Finland (Nomadiclab), with video are not yet supported, but implementation his main focus on service enablers, multimedia applica- work is ongoing and follows the JSR 309 Media tions, privacy, and security. Server Control API (http://jcp.org/en/jsr/ HEIDI-MARIA RISSANEN received her M.Sc. degree in commu- ______detail?id=309). Support for streaming media is nications engineering from Helsinki University of Technolo- still an open issue since the current Java ME gy, Finland, in 2007. She joined Ericsson Finland in 2005. platform does not support it. Since 2006 she has been working as a research scientist at

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TOPICS IN DESIGN &IMPLEMENTATION Deployment of Contextual Corporate Telco Services Based on Protocol Adaptation in the NGN Environment

Alejandro Cadenas and Antonio Sánchez-Esguevillas, Telefónica I+D Belén Carro, University of Valladolid

ABSTRACT The technology to capture such user information becomes instrumental for the deployment of Deployment of contextual services is usually context-aware services. While detecting the pres- constrained to specific areas where contextual ence of the user in a specific location may behavior can be obtained, mainly due to coverage require location capabilities from the access net- limitations of context acquisition devices. Although work, a global positioning system (GPS) on the end customers highly appreciate contextual ser- user terminal, or even a radio frequency identifi- vices, those limitations make such services difficult cation (RFID) tag carried by the user, aspects to commercialize. In this article we present a prac- like the emotion or current activity of the user tical deployment of a contextual service offered by are more difficult to capture or detect. a convergent telecommunications operator, whose On top of that, even if the context of the user functionality is to provide intelligent context-based can be properly detected, the sensor may be call routing and rerouting, orchestrated from the deployed in a given location or area (e.g., an operator’s service layer. It is based on IMS control enterprise building), and the context awareness layer capabilities to properly capture the situation of the service can only be obtained for that area of the end user in a ubiquitous coverage area. The in which the user information can be detected. user’s context is stored in a network-centric ele- These issues become important barriers to ment in order to leverage that information across the successful deployment of commercial con- different services, optimizing the system by sumer context-aware services by telco operators, increasing the quality of the information captured since when targeting the mass market global cov- and processed. This implementation proves that erage for the services is required. value-added contextual services may be built effi- The existing implementations of context- ciently today using available products and proto- aware services are in several cases limited to lab- cols. Since contextual services will likely be a oratory environments or small areas [2]. valuable part of a service provider’s portfolio, this Information about the user context is usually implementation can help creators of new contex- processed by a service platform where the con- tual services to meet cost and time-to-market text-aware service is executed [3]. This platform objectives. is connected to the user context sensing device. Accordingly, in these scenarios a tight coupling INTRODUCTION exists between the application and the sensors. That is typically known as a vertical service layer Context-aware applications are one of the new architecture in which all information required paradigms in telecommunications commercial for the service execution is obtained by and pro- environments, and significant research has been cessed at the service execution platform, and no done on this topic [1]. These applications are sharing of user context information exists among based on appropriate sensing or detection mech- the different context-aware service platforms. anisms whose objective is to identify the situa- The telco operators have a relevant role on tion, or context, of the user that will consume the such activities, especially the convergent opera- context-aware service. This sensing mechanism tors (i.e., those operators that own both fixed can be either push or pull, depending on the spe- and mobile networks). This is due to the fact cific sensor device and magnitude detected. Con- that contextual services deployed by convergent text is a diverse concept. It can range from the operators can efficiently make use of both fixed physical presence of the user in a given room to and mobile access networks to process the user the emotional situation of a user that may affect information obtained by contextual sensors. the way some services are delivered. It also has a Such diversity of the access network means a sig- strong dependence on the time in which it is nificant increase in coverage of the context- acquired, as some types of information have aware service. expiration times (location, activity, etc.). Hosting the context-aware platforms at the

telco operator service layer also offers advantages thanks to the sharing of user context infor- Application servers Enablers mation among different services. Therefore, the captured contextual information can be reused by any existing application in a horizontal way. This means that the contextual information is highly exploited across multiple applications. Etc Based on such objectives as horizontality of the contextual information across the service Presence Context layer and the coverage range of the context- aware services, a telco contextual architecture is presented in this article. This architecture uses the capabilities provided by the IP multimedia IMS subsystem (IMS) convergent control layer specified by Third Generation Partnership Project (3GPP) [4]. Details about the architecture design, protocols used, and a first service implemented and Access Access deployed taking advantage of such capabilities network 1 network 2 are also described. Different alternatives and options chosen are provided, as well as details of an implementation project of a context-aware service. The article closes with lessons learnt and conclusions.

IMS-BASED ARCHITECTURE: Figure 1. Target network architecture based on IMS, interoperable with differ- CONTEXT ENABLER ent access networks. Worldwide operators are currently evolving toward network convergence as well as horizontal architectures of their service layers. Such evo- rate way. In addition, the timing to introduce lution is driven by cost reduction and quality of such elements into the operator service domains service (QoS) objectives, and is based on the is appropriate, given that services compatible technology of IMS, whose main protocol is Ses- with the IMS control layer are becoming com- sion Initiation Protocol (SIP), specified by the mercial realities in the short or mid-term, and Internet Engineering Task Force (IETF) in such integration activities among different ser- Request for Comments (RFC) 3261, which pro- vice platforms are currently taking place. The vides interworking capabilities with different IMS-based architecture with the context enabler types of access networks. is presented in Fig. 1. Apart from other key advantages oriented to The main advantages of such anarchitecture security, authorization, accounting, and authenti- are the following: cation (AAA), QoS, and so on, IMS is a suitable Ubiquity of context-aware service: It can be framework to deploy the elements required to provided to the user regardless of geographical handle the information about user context. In location and type of device. This advantage is IMS terminology, this is precisely the concept based on the interoperability capabilities of the called enabler [5]. IMS control layer. IMS interoperability [7] with An enabler is an element of the service layer WiFi, cellular (3.5G, 3G, 2.5G), or fixed access accessed through IMS. It is not a service itself, networks guarantees that any type of sensor used but an entity whose objective is to provide addi- to capture the user context or situation will be tional information to the existing services or able to notify the context enabler of such infor- applications at the service layer. An example is mation for its storage and processing. the presence server [6], specified by the Open Enrichment of the contextual information: Mobile Alliance (OMA). The presence server The possibility of connecting a higher number of stores and manages the presence information of sources of context information to the context the end users, and provides presence informa- enabler will make the context information stored tion to any entity of the service layer that may at it more robust [8]. Different types of sensors request it (with appropriate permissions). capturing different types of information (pres- Signaling exchanged between IMS enablers ence, activity, battery level, noise level, etc.) will and application servers located at the service provide more accurate information about the layer is based on SIP SUBSCRIBE/NOTIFY user. methods, which provide a flexible and robust Horizontal service layer: The fact that the procedure for the services to subscribe to the context information is stored at a single logical updates of information handled by the enabler. point at the service layer enables complete shar- Therefore, a context enabler, handling infor- ing of the context information across all service mation about the context of the user coming layer application servers. In order to achieve from different sensors, fits perfectly in the IMS that, services need to get subscribed to the con- standard architecture as opposed to the vertical text enabler for updates of the specific user con- approach, in which each and every service will text. The context information storage will be a handle the user context information in a sepa- cluster of servers that will meet all requirements

IEEE Communications Magazine • April 2010 35

of the project, and have driven many of the implementation and design decisions. Presence DESIGN PHASE During the design phase the enterprise telecom system is analyzed. The global architecture is depicted in Fig. 2, including both the mobile and SIP fixed domains, with the separate access networks, public land mobile network (PLMN) and public switched telephony network (PSTN). The corporate fixed communications are based on IMS customer premises equipment (CPE), which is the private branch exchange (PBX) located at PLMS PSTN the premises of each enterprise, but owned and OBG operated by the telco operator. There are a number of corporate fixed lines (extensions) connected to the PBX, typically one fixed line per end user. The PBX will route the IP PRI PRI incoming/outgoing calls through the external connection, IP-based or via a primary rate inter- CTI face (PRI) connection to the PSTN. In addition, the PBX will also provide a number of enterprise communication services that are not usually available to residential and consumer PBX subscribers, such as call reject, call hold and retrieve, call diversion, call transfer, and some others. PC-based softphones may also get external access through the PBX. Eventually, a large corporation may decide to manage their internal communications. In that scenario the enterprise still requires a PBX with external access provided by a telco operator, so the system implementation is exactly the same as if the internal Figure 2. Designed architecture to implement, with the presence server and communications were also operated by an exter- OBG element. Both the mobile and fixed communications domains are nal telco operator. An additional element, the depicted. operator business gateway (OBG), is also included in the architecture. This element is justified in the implementation phase. The corporate mobile communications are of scalability and fault tolerance. Such informa- based on a contract with the mobile telecom tion collection makes the development of con- operator, which provides mobile numbering textual applications quicker and cheaper. translation services when calls are made between mobile phones of the same corporation (using a short numbering scheme), in addition to others DESIGN AND IMPLEMENTATION very similar to the ones provided by the PBX on HASES OF THE RCHITECTURE the fixed side. Such services are usually provided P A via intelligent network protocols from the service Context-aware services are suitable for different layer at the mobile network. market segments. However, the specific case In order to capture information on the situa- presented in this article is oriented to enterprise tion of a user from a fixed phone, a trigger is users, with the following characteristics: implemented at the PBX. That trigger converts • End users (enterprise employees) usually the PBX in the actual context sensing device, have different types of phones: corporate and generates a signaling notification upon any mobile phone, office fixed desk phone, and event that takes place at the PBX for a given in some cases a corporate PC softphone extension. An incoming call, outgoing call, call application. end, call cancel, and so on will generate a notifi- • Enterprise users are more tolerant of learn- cation from the PBX to an external monitoring ing curves and configuration of services application. than the residential market. In the presented design that event notifica- • Specific development costs can eventually tion is carried over a computer telephony inter- be supported by the enterprise customer if face (CTI) protocol supported by the PBX, that means a significant enhancement of which is oriented to report specific telephony the telecom service obtained by the enter- events. Although there are other choices, the prise. option selected is the Computer Supported Several parameters are considered critical Telecommunications Applications (CSTA) Pha- during design, implementation, and deployment seIII protocol, specified by the European Com- of services for enterprise segment. Those are puter Manufacturers Association (ECMA) [9], time to market, interoperability of the different supported by (or on the roadmap of) many PBX architectural elements, and development costs. manufacturers. This protocol consists of a com- These key parameters have been the main focus plete call control signaling specification, imple-

36 IEEE Communications Magazine • April 2010

mented through a set of XML commands whose premises), meaning a big number of PBXs in a format is defined by ECMA, carried on two pos- wide geographical area (1000+ PBXs deployed Different manufac- sible transport options, SIP or Simple Object in several cities). There may also be enterprise Access Protocol (SOAP)/HTTP. In addition, the customers with a much smaller geographical dis- turers would mean PBX may also receive telephony commands tribution (or no distribution at all). different CSTA from external computing functions over CSTA That is a critical aspect for the transport net- PhaseIII flavors. PhaseIII (release an ongoing call, reject an work. Initially, global connectivity over a SIP incoming call, establish a call to a specific desti- overlay was considered. However, given the geo- This implementation nation, etc.). The CSTA PhaseIII XML message graphical distribution of the network elements issue affected the sent to the PBX to clear a specific connection (a and the different network domains the signaling voice call) is the following. needs to traverse (in some cases operated by the architecture itself, enterprise customer itself), a transport protocol calling for the with better interoperability and connectivity definition of an is HTTP/SOAP. Given that after preliminary namely the OBG, laboratory testing the estimated link bandwidth 123456789 consumption imposed by this signaling load is whose mission is to tel:+34913374005 minimum (on the order of hundreds of kilobits solve the inter-PBX per second), the best option available was to use vendor compatibility the data link purchased by enterprise customers at each premises to get external data connection. problem. The CSTA PhaseIII events generated from In those premises where the external data access the PBX to an external entity are information is heavy loaded, additional digital subscriber line about the context of the user. (xDSL) access may be deployed (possible but The procedure to capture similar context unlikely). information at the mobile network side is the Another key aspect that affected the imple- presence and registration status management of mentation even more than the geographical dis- the mobile cellular networks, a capability already tribution is the diversity of PBX manufacturers. available in commercial mobile networks. Such There will be several PBX manufacturers capability can provide updated information involved (initially two manufacturers were about the location, registration status, and avail- involved, but additional ones may be included in ability of cellular devices. In our mobile network order to offer these services to all enterprise cus- the location and registration information is tomers). Getting all manufacturers involved to stored at the home location register (HLR) of implement a coherent CSTA PhaseIII protocol the home network of the mobile device, and is with the same behavior of PBXs in a robust way updated during registration procedures via SS7 was an unrealistic approach. PBXs from differ- signaling protocols. The registration information ent manufacturers would have different imple- is sent from the mobile network to the conver- mentations of CSTA PhaseIII, which would gent service layer via a SIP interface, through a make it impossible to get all the systems working protocol gateway deployed at the mobile net- properly with tight time-to-market constraints. work. Different manufacturers would mean different The objective is to route all such contextual CSTA PhaseIII flavors. This implementation information to a context enabler located at the issue affected the architecture itself, calling for convergent service layer, accessible from both the definition of an additional element, the fixed and mobile service layers. However, the OBG, whose mission is to solve the inter-PBX development of a context enabler platform was vendor compatibility problem. The function of not considered within the timeframe of the pro- the OBG is to act as a single entry point of con- ject due to the availability of existing elements textual signaling traffic from all the PBXs. All already deployed in the operator service layer the particularities of different PBX manufactur- which can cover that need. The simplicity of the ers would be considered at that element, and the context model to be followed (presented below) OBG would perform adaptations from the dif- made it clear that having a dedicated platform ferent CSTA PhaseIII flavors from different for context management was suboptimum given PBX manufacturers into a CSTA PhaseIII imple- the time to market objectives. The development mentation that is standard and stable within the of a complete context management enabler operator service layer domain. So the OBG became a parallel working direction with differ- would deal with the interoperability aspects ent time constraints. among the different interface implementations The existing platform where the available from the variety of PBX manufacturers. context of the user will be located is the OMA The drawback of including this new element presence server. Context information will be in the architecture is mainly the significant routed to the presence server, and the context of increase in the development costs of the project. the user will be stored as a parallel presence sta- However, such protocol adaptation in the end tus. decreased the operational costs significantly. So it was proven to be the right decision also in IMPLEMENTATION PHASE terms of global costs. This is one of the main A very important feature of the system on the project conclusions presented below. fixed side is the wide geographical distribution of Finally, it is worth clarifying that, since the the PBXs. There is a PBX in each customer OBG has been defined as a single entry point premises (enterprises with several distributed for CSTA PhaseIII signaling from the PBXs, it is

IEEE Communications Magazine • April 2010 37

a network element located at the operator ser- The flexibility of the architecture presented in The delay observed vice layer. Accordingly, the interface between the previous sections is demonstrated with the the OBG and the context enabler, as well as with intelligent routing service presented in this sec- for a single CSTA any other service, will be an operator network tion. The basic use case of the service is present- PhaseIII signaling protocol. Given that this is a convergent archi- ed in Fig. 3, in which an incoming call arrives to transaction from PBX tecture based on an IMS core network, it was the PBX targeting an employee subscribed to quickly considered to implement such an inter- the intelligent routing service [13]. to the hosted service face over a SIP transport protocol. This would In Fig. 3, when a call arrives to the PBX from is in the order of make any later integration between the OBG the PSTN, the PBX temporarily stops the call and additional services much easier. progress and sends a CSTA PhaseIII event to 100 ms. For a Since SIP is chosen for the interface between the OBG, requesting a route for the call complete scenario in the OBG and the context enabler, the CSTA (CSTA_RouteRequest). The trigger to the which a call is routed PhaseIII messages received from the PBXs over hosted service is executed by the PBX before a HTTP/SOAP will be parsed by the OBG and call is routed to the destination extension, taking and the presence adapted to standard CSTA PhaseIII over SIP into account that incoming calls can also origi- status is updated, (uaCSTA), screening any particularity of the nate from another internal extension of the PBX manufacturer implementation. The final PBX. the whole delay is in XML CSTA PhaseIII message is then embedded The OBG performs the protocol adaptations the order of 500 ms. in the body of a SIP INFO method, as stated by required based on the PBX manufacturer and the uaCSTA PhaseIII specification [10]. The sends the request for a route to the intelligent CSTA PhaseIII XML message is the same routing service by including the same regardless of the transport protocol (SIP or RouteRequest XML over a SIP INFO method. HTTP/SOAP). The intelligent routing service has a specific business logic implemented to select the destina- INTEROPERABILITY TESTING tion of the call. That service logic includes, at a Both the selection of SOAP as the protocol for the high level, checking a list of prioritized destina- CSTA PhaseIII message transfers and the inclu- tions and the situation of each one by querying sion of OBG in the architecture respond to the the IMS presence server or additional informa- objective of improving interoperability with mini- tion repositories like corporate calendar services. mum development. So interoperability testing was If the destination user is online at any of his/her an important phase before commercial rollout. phone devices, the service selects that destina- Again, to optimize time to market, an agile tion and responds to the OBG with a command development mechanism [11] is followed. Short (CSTA_RouteSelect) including the destina- development cycles are implemented (1–2 mo), tion for the pending call. and different levels of interoperability testing were Again, the OBG performs protocol adapta- performed at the end of each development cycle. tions as required, and sends to the PBX the selected route for the call that is waiting to be PBX Level — A project structure based on delivered. This selected destination may be a sequential functional iterations is followed joint- fixed extension (connected to the PBX or to ly by the PBX manufacturers and the operator. another PBX) or a mobile extension. If it is a Periodically, the manufacturer releases a set of mobile destination, the PBX will then need to functionality, and signaling compliance is validat- forward the call through the public mobile net- ed by the operator via a simulator [12] that can work. The selected destination might even be a be quickly adapted to the special implementa- PC-based softphone that the PBX can reach tion of each PBX manufacturer. through the corporate private network. Once the call is successfully established, the OBG Level — The OBG element also needs to be context enabler is updated with the new user validated. The same procedure as with the PBX context, again via CSTA PhaseIII notification. manufacturers is followed. The engineering simula- Similar services can be designed, using the tion tool is also used in this interoperability testing. contextual information stored at the presence server (or a dedicated context enabler platform), End-to-End Level — Finally, all elements are making use of the architectural mechanisms installed in a laboratory environment with real deployed. phones and fixed PBX extensions. Some interop- In terms of performance figures, the delay erability issues are still identified, but this phase observed for a single CSTA PhaseIII signaling is mostly a functional validation by the operator. transaction from PBX to the hosted service is on the order of 100 ms. For a complete scenario in which a call is routed and the presence status is THE SERVICE USE CASE DEPLOYED: updated, the whole delay is on the order of 500 ms. ONTEXT WARE Both values are consistent with the figures observed C -A in a laboratory environment, with very small vari- CALL ROUTING SERVICE ance values. However, much stronger performance testing is required in a later deployment phase, as There is currently no known (as far as we are the current number of customers is still growing. concerned) commercially deployed convergent service that is able to route incoming calls to ESSONS EARNED corporate lines (PC, mobile or a fixed desk- L L phone) to the appropriate destination based on During the design of the architecture and the a specific situation (e.g., context) of the employ- deployment, several lessons can be identified to ees associated with the corporate lines. consider in future developments with similar

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Public Intelligent Presence Due to the limited network PBX OBG IMS routing service server complexity of the INCOMING CALL first service that will use the contextual Stop call information stored at [WSCSTA]: Incoming call Event the Presence Server, [uaCSTA]: Incoming call Event the number of [uaCSTA]: Incoming call Event possible context statuses is small. The range of values Contextual [SIP]: SUBSCRIBE might be increased service logic [SIP]: NOTIFY for other contextual services with little [uaCSTA]: Selected Destination effort.

[uaCSTA]: Selected Destination

[WSCSTA]: Selected Destination

Call routing

[WSCSTA]: New Context Status

[uaCSTA]: New Status

Context update

Figure 3. Signaling flow for the intelligent routing service, based on the contextual architecture presented.

purposes. significant configuration updates. The capabilities and protocols supported by the Due to the limited complexity of the first ser- different PBX manufacturers are very diverse. vice that will use the contextual information That happens in any context-aware system stored at the presence server, the number of deployed by telco operators. The types and sources possible context statuses is small. The range of of user context are also very diverse, and interop- values might be increased for other contextual erability and protocol adaptations are required. services with little effort. During the analysis phase, it was clear that An additional element to develop was a sin- the number of protocols used within the opera- gle entry point into the operator network that tor network should be minimized to avoid inter- provides signaling adaptation into a secure and operability issues. Since the control layer at the standard protocol. The benefits for the testing operator network is IMS, the protocol used with- phase, the isolation of PBX vendor-specific in both that domain and the service layer is SIP. issues, and the subsequent securization of opera- This means a simplification of the transport net- tor service layer generated project benefits that work configuration at the operator network. If a justified the associated development cost. different/additional protocol is to be used, it would require modifications of the traffic flows ONCLUSIONS AND UTURE ORK and verifications of connectivity across existing C F W firewalls. From an operational perspective that In this work an architecture to handle the con- would mean huge problems. text information of telco users is presented. This The transport protocol chosen to carry the information is sent from the different access net- information from PBX to the operator network works to a context server (enabler) hosted at the is SOAP/HTTP. This option is selected as operator service layer. Due to time to market opposed to SIP because of the simplicity of the reasons, the context management server is collo- initial deployment and subsequent upgrades or cated with the OMA presence server. maintenance tasks. The data networks deployed This proposed architecture is designed to be to connect customer premises with the operator future-proof and flexible to allow other services are not usually prepared to support SIP without to take advantage of the user context informa-

IEEE Communications Magazine • April 2010 39

tion, becoming with small development costs Future Mobile Services,” IEEE Commun. Mag., vol. 42, context-aware services. In order to do that, the no. 9, Sept. 2004, pp. 63–69. This proposed [9] ECMA Standard 348 “Web Services Description Lan- signaling protocols within the operator service architecture is guage (WSDL) for CSTA Phase III,” June 2009. layer are properly selected. [10] ECMA Tech. Rep. TR/87, “Using CSTA for SIP Phone designed to be A context-aware convergent service is User Agents (uaCSTA),” June 2004. designed with this architecture. The objective of [11] M. Fowler and J. Highsmith, “The Agile Manifesto,” future-proof, and Aug. 2001; http://agilemanifesto.org/ the service is intelligent context-aware incoming [12] J. M. González, A. Cadenas, and O. Solá, “Adaptation flexible to allow call routing for a corporate telephony network Middleware to Enable Presence and Call Control for other services to take (both fixed and mobile). Corporate Fixed Lines: Evolution to Convergent Net- The future lines of work are twofold: work over IMS,” NGNM ‘08, Sept. 2008. advantage of the [13] A. Cadenas et al., “Distributed PBX Gateways to • Design and integrate new services into this Enable the Hosted Enterprise Services Architecture in a user context architecture, enhancing the added value of NGN Scenario,” 1st ITU-T Kaleidoscope Academic Conf., May 12–13, 2008, pp. 203–10. information, the operator commercial portfolio. • Develop a dedicated context management becoming with small platform where specific and more complex BIOGRAPHIES

development costs information processing algorithms may be ALEJANDRO CADENAS [M] ([email protected])______is currently a pro- implemented, including context semantic ject manager in Telefónica Research and Development, context-aware processing and user profiling, among others. focusing on IMS, NGN, and innovation in end-user services, services. network evolution of the operator infrastructure toward user-centric services, context-aware hosted services, and REFERENCES protocol adaptations. Previously he was a senior systems engineer in Motorola Inc. for several years workingon net- [1] D. Saha and A. Mukherjee, “Pervasive Computing: A work design and IMS control layer design. He is a Ph.D. Paradigm for the 21st Century,” Computer, vol. 36, no. candidate researching convergent contex-aware architec- 3, Mar. 2003, pp. 25–31. tures and interoperation with telco services. [2] J. Sun, Z.-H. Wu, and G. Pan, “Context-aware Smart Car: From Model to Prototype,” J. Zhejiang Univ. — Sci- ANTONIO SANCHEZ-ESGUEVILLAS [SM] (a.sanchez-esguevillas@______ence A, vol. 10, no. 7, July 2009, pp. 1049–59. ieee.org) has managed innovation at Telefónica (both cor- [3] M. Baldauf, S. Dustdar, and F. Rosenberg, “A Survey on porate and R&D), Spain. He is also an adjunct professor at Context-aware Systems,” Int’l. J. Ad Hoc Ubiquitous the University of Valladolid. His research interests relate to Comp., June 2007, pp. 263–77. services and applications. He is an Editorial Board member [4] 3GPP TS 23.228 “IP Multimedia Subsystem (IMS): Stage of IEEE Communications Magazine and IEEE Network, 2”; http://www.3gpp.org founder and Chairman of the IEEE Technology Manage- [5] H. van Kranenburg et al., “A Context Management ment Council Chapter Spain, guest editor of IEEE Wireless Framework for Supporting Context-aware Distributed Communications, IEEE Communications Magazine, and IEEE Applications,” IEEE Commun. Mag., vol. 44, no. 8, Aug. Network, and has served on the TPCs of ICC, GLOBECOM, 2006, pp. 67–74. PIMRC, WCNC, HealthCom, CCNC, and VTC. [6] C. Chi et al., “IMS Presence Server: Traffic Analysis and Performance Modeling,” IEEE Int’l. Conf. Net. Protocols, BELÉN CARRO ([email protected])______is an associate professor at Oct. 19–22, 2008, pp. 63–72. the University of Valladolid, where she is director of the [7] M. Schmidt et al., “IMS Interoperability and Confor- Communication and Information Technologies (CIT) labora- mance Aspects,” IEEE Commun. Mag., vol. 45, no. 3, tory. Her research interests are in the areas of service engi- Mar. 2007, pp. 138–42. neering, IP broadband communications, NGN and voice [8] S. Arbanowski et al., “I-centric Communications: Per- over IP, and quality of service. She has extensive research sonalization, Ambient Awareness, and Adaptability for publications experience as author, reviewer, and editor.

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TOPICS IN DESIGN &IMPLEMENTATION The Design and Implementation of Architectural Components for the Integration of the IP Multimedia Subsystem and Wireless Sensor Networks

May El Barachi, University of Quebec Arif Kadiwal, Nuance Communications Roch Glitho, University of Quebec and Concordia University Ferhat Khendek, Concordia University Rachida Dssouli, Concordia University and United Arab Emirates University

ABSTRACT INTRODUCTION The IP multimedia subsystem is becoming the The Third Generation Partnership Project de facto standard for IP-based multimedia ser- (3GPP)-defined IP multimedia subsystem (IMS) vices, while wireless sensor networks are gaining is becoming the de facto standard for IP-based in popularity due to their ability to capture a multimedia services [1]. It consists of an overlay rich set of contextual information. Integrating control and service layer that is deployed on top the sensing capabilities of WSNs in the IMS can of IP-based mobile and fixed networks in order open the door to a wide range of context-aware to enable the seamless provisioning of IP multi- applications in areas such as wireless healthcare media services to end users. Wireless sensor net- and pervasive gaming. We have previously pro- works (WSNs) are formed by a set of distributed posed a presence-based architecture for sensor nodes that collaborate to monitor physi- WSN/IMS integration. This architecture relies cal, environmental, and physiological conditions on two key components: a WSN/IMS gateway [2]. Such networks are increasingly popular acting as an interworking unit between WSNs because they can capture a rich set of contextual and the IMS; and an extended presence server information that can be used for a wide range of serving as a context information management applications. node in the core network. In this article we focus Context awareness is the ability to use con- on the design and implementation of these two textual information to provide relevant informa- components. Furthermore, two applications (a tion and/or services to users. By integrating the pervasive game and a personalized call control sensing capabilities of WSNs in the IMS, a rich application) are used to concretely show how set of contextual information can be exploited to new applications can be developed using our provide new and personalized multimedia ser- architecture. Performance has also been evaluat- vices to IMS users. Examples of such services ed. Several important findings were made in the include wireless healthcare applications monitor- course of this work; one is that the IMS integra- ing and interpreting patients’ physiological data tion with a large and evolving variety of WSNs and offering them personalized medical assis- may be a never-ending endeavor — the gateway tance for problematic health conditions; perva- This article is an extended requiring constant upgrading due to the lack of sive games involving interaction with version of the article pre- standard APIs for the interaction with sensors physical/virtual objects and characters, and using sented at IEEE VTC produced by different vendors. Another finding the game context to adapt the players experi- 2009-Spring under the is that while the introduction of context as an ence; and lifestyle assistance applications making title of “The Design and application building block in the IMS ensures use of users’ situational information to assist Implementation of a the availability of additional contextual informa- them in their daily activities (e.g., training and Gateway for IP Multime- tion in the network and enables fast and easy shopping). dia Subsystem/Wireless development of context-aware applications, the We have previously proposed a presence- Sensor Networks Inter- lack of mature IMS application development based architecture for WSN/IMS integration. working.” toolkits remains a roadblock. This article focuses on the design and implemen-

We note that several Pex P b wn types of PAs are WSN/IMS Extended IMS core Gateway PS (AS) entities (e.g. WSNs (PEA) (Internal) CSCFs) defined in the 3GPP architecture. One of Proprietary Pwp Pex these types is the sensors a ISC Presentity presence proxy Watcher presence proxy interfaces Presence External P-CSCF S-CSCF I-CSCF S-CSCF P-CSCF Agent (PEA) responsible of Pw = Pw = Pw = publishing Mw ISC Gm HSS information provided IMS AS IMS user by external (E.g. GS) applications entities/networks about the user. Figure 1. The WSN/IMS integrated architecture.

tation of the key components of our architec- To achieve WSN/IMS integration, we ture, and illustrates how applications (leveraging assigned the role of PEA to the WSN/IMS gate- its capabilities) can be built, using two concrete way, which will publish information captured by examples. Furthermore, the article presents the WSNs (after proper processing/formatting) to an results of the performance evaluation we con- extended presence server (capable of managing ducted using one of the developed applications, the different types of information provided) via and reports on what we learned from this pro- a trusted node (a presence proxy) over the Pexa ject. interface. In addition to the indirect interactions The next section gives an overview of the pre- over the Pexa interface, the WSN/IMS gateway viously proposed architecture. In the following directly interacts with the PS over the Pexb inter- section, the architectural components’ design is face for the management of subscription policies presented. This is followed by a description of (enabling information access control). We note the prototype implementation and proof-of-con- that the WSN/IMS gateway can be considered cept applications. We then present the perfor- specialized user equipment, only used for the mance evaluation. The last section ends the management and publication of sensory informa- article with a discussion of related work and the tion in the 3G network. lessons learned. Other entities such as IMS application servers (e.g., game servers) and IMS user applications can access the information managed by the PS AN OVERVIEW OF THE WSN/IMS via presence proxies using the Pw interface (cor- NTEGRATED RCHITECTURE responding to the IMS service control [ISC] and I A Gm interfaces), while IMS core network entities Figure 1 depicts the architecture we proposed in acting as watchers (e.g., CSCFs) can directly [3] to enable the integration of WSNs in the access this information using the newly defined IMS. Pwn intra-operator interface (without triggering This architecture is an extension of the 3GPP the generation of charging records). It should be presence architecture, which focuses on the noted that the XML Configuration Access Pro- management and dissemination of user presence tocol (XCAP) [4] is used over the Pexb interface, information (a subset of context information) while an optimized version of the SIMPLE pro- within the network. The 3GPP presence archi- tocol [5] is used over the Pexa, Pw, and Pwn tecture relies on five main functional entities: interfaces. presence agents (PAs), which make information To enable the management and dissemina- available to the network in a standard format tion of the collected sensory information, we and via standard interfaces; the presence server proposed an extension of the standard presence (PS), responsible for the management of infor- information model (i.e., the presence informa- mation published by agents; the presence list tion data format [PIDF]) in order to allow the server, responsible for group list management; representation of the additional types of infor- presence proxies, acting as inbound/outbound mation captured by WSNs (i.e., spatial, physio- proxies to the presence network by performing logical, and environmental data) in a standard routing, security, and charging functions, and format, while allowing the distinction between whose roles are assumed by call session control the different types of entities to which the infor- functions (CSCFs); and watchers, acting as information relates, as follows: To allow the encapsu- mation consumers. We note that several types of lation of physiological and environmental data PAs are defined in the 3GPP architecture. One within a presence document, two new subele- of these types is the presence external agent ments (physiologicalData and environ- (PEA), responsible for publishing information mentalData) were added to the existing tuple provided by external entities/networks about the element. Each of these subelements was further user. divided into other subelements. For instance, the

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The abstraction layer Abstraction layer is responsible for Info management functions Support functions conveying the information captured Info rep. Data model rep.

by WSNs to the IMS, Info XML ISIM acquisition - PIDF Registration Processed formatter and security app. after the proper module WSN info - Mapping processing and table formatting. This layer Policies consists of two types rep. Capabilities publication of functions - Subscription (i.e., information Extended PEA authorization policies management - Publication Trigger Publisher Events policies Information functions and handler monitor access control support functions).

WSN interface 3G interface

Connectivity layer

Figure 2. The WSN/IMS gateway architecture.

complex element environmentalData is THE WSN/IMS GATEWAY ARCHITECTURE divided into ambientTemperature, soundLevel, lightIntensity, and rela- The WSN/IMS gateway plays a key role in our tiveHumidity subelements, in addition to a architecture by acting as an intermediary qualityInfo subelement and any number of between WSNs and the 3G network. Figure 2 extension subelements. depicts the proposed gateway architecture, which For spatial information we leveraged the consists of two layers: a connectivity layer and an existing GEOPRIV extension data element (spec- abstraction layer. The connectivity layer includes ified in RFC 5491) for its representation, and a dual networking interface, ensuring connectivi- extended one of its child elements (civicLoc) ty to both WSNs and the 3G network. The with refined location information such as room abstraction layer is responsible for conveying the ID, displacement direction, and relative distance information captured by WSNs to the IMS, after to other. Finally, to enable the distinction the proper processing and formatting. This layer between different types of entities (i.e., person, consists of two types of functions (i.e., informa- object, place, or network) to which the information management functions and support function may relate, we added two new mandatory tions) that are described in detail in the coming attributes, entityType and entityDescrip- subsections. tion, to the existing presence element. In our architecture, three information publi- The Support Functions — The support func- cation models were employed to enable flexible tions are realized by the following modules: the and resource-efficient information exchange registration/security module, capability publica- within the network: interval-based publications, tion module, and information access control in which information is published at regular time module. intervals; event-based publications, in which The registration/security module is the first information is published when certain events are module invoked when the gateway (GW) is put detected; and trigger-based publications, in in service. It interacts with the ISIM application which information is published upon receipt of a (contained in the gateway’s SIM card) to get the publication trigger from the PS. information required for IMS registration and security association establishment (e.g., public/private identities and the long-term ARCHITECTURAL secret), builds the first SIP REGISTER message, OMPONENTS ESIGN and interacts with the capabilities publication C ’ D module that inserts the gateway capabilities As shown in the previous section, our architec- information (e.g., the type of information pro- ture relies on two main components in its opera- vided by the GW) in the message body. The reg- tion: the WSN/IMS gateway and the extended istration module then carries out the rest of the presence server. In the subsequent subsections, IMS registration procedure normally. we describe the designs of these two compo- After the registration phase, the information nents. access control module communicates with the PS

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to set the required subscription authorization policies (which are preconfigured in the GW’s policies repository). Those policies are used by the PS to install filters that determine which - Extended PIDF watchers are allowed to access the information XML/parser/ - Contextual info Info/policies related to a certain contextual entity, thus pre- formatter - Info access policies repository serving information privacy. In addition to subscription policies, the GW’s policies repository also contains publication policies indicating the types of information that should be published at Publication and Authentication subscription Trigger Events regular time intervals and the ones that are pub- generator Notifier monitor and authorization lished based on events’ detection. manager module

The Information Management Functions — The information management functions are performed by a set of information acquisition mod- Presence service logic ules, an XML formatter, an extended PEA, and three repositories. The first repository (the data model repository) contains the extended PIDF we SIMPLE stack (SIP servlet API) defined as an information model and mapping tables correlating IMS entities’ IDs (identifying the entities whose information is being published in the IMS) to sensor IDs (identifying the sen- Figure 3. The extended presence server architecture. sors capturing information related to a certain entity), while the second (the information repository) contains the processed WSN information 30°C), and keeps interacting with the informa- that is persistently stored in the GW for future tion repository to detect the occurrence of those publications. The third repository is the policies events. Once an event is detected, the events repository presented above. monitor interacts with the publisher, which will The information acquisition modules are spe- fetch the needed information and publish it cialized components that enable the interaction (after proper formatting) to the PS. As for the with various WSNs. There is one acquisition trigger handler, it does not actively publish any module per WSN type. Such a module is capable information. However, once it receives a publi- of extracting sensor-specific data from WSN cation trigger (from the PS), it contacts the pub- messages, and preprocessing this information (by lisher, which will convey the needed information performing data fusion and consistency check- to the PS. ing) before storing it in the GW’s information repository. When the WSN comes with a mid- THE EXTENDED PRESENCE dleware (e.g., the one proposed in [6]), the mod- SERVER ARCHITECTURE ule interacts with the middleware instead of interacting directly with the WSN. In this case Figure 3 depicts the software architecture of the less or no preprocessing may be required, extended presence server serving as the context depending on the middleware capabilities. management node in our system. The extended PEA represents the heart of the This architecture consists of protocol and ser- WSN GW. It publishes the WSNs’ information vice-related components. The protocol support- to the IMS, based on the publication policies ed in this case is the SIMPLE protocol, which is defined in the GW. Two modes of publications accessible via the SIP servlets application pro- are supported by the extended PEA: the proac- gramming interface (API). The service compo- tive mode, in which information is actively pub- nent consists of a presence service logic module lished by the GW at regular time intervals or implementing the logic of the PS engine. This when certain events are detected; and the reac- module relies on several submodules in its oper- tive mode, in which information is only pub- ation: a publication/subscription manager that lished upon receipt of a trigger from the PS. handles information publications and subscrip- These two modes of publication are realized tions from presence agents and information by the PEA submodules as follows: Based on the watchers; a notifier that creates and sends infor- publication policies, the publisher saves a list of mation notification messages based on received information that should be proactively published subscriptions (these notifications could be sent at regular time intervals; following those inter- following regular time intervals or upon the vals, it consults the information repository to detection of events); an events monitor that retrieve the needed information, which is then monitors the collected information and detects passed to the XML formatter (if the information the occurrence of events that could possibly lead is not yet in the standard format). The XML for- to information notifications; a trigger generator matter consults the IDs’ mapping tables and the that generates publication triggers to prompt the extended PIDF in order to represent the pro- publication of information that is missing or not cessed information in a standard format, and fresh enough in the network; and an authentica- then returns the resulting XML document to the tion and authorization module that is responsi- publisher, which publishes it to the PS. Similarly, ble for the authentication of publishers/ the events monitor saves a list of information to watchers and the enforcement of subscription be proactively published upon detection of authorization policies. It should be noted that events (e.g., publish temperature when above these submodules rely on an XML parser/for-

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Sense Call [9] is a personalized call control application previously developed in our labora- Extended PS (SIP servlet) Server side of tory as part of another project in which a web- SIP container game (SIP servlet) service-based GW was used to enable WSN/IMS applications’ interaction with sensors. This appli- GW Server side of SenseCall App. cation monitors users’ locations and enables the SIP / SIMPLE (SIP servlet) automatic (pre-booked) establishment of a call between two colleagues when they are in their respective offices. To illustrate the capabilities of Emulated CSCF Emulated our system, Sense Call was remodeled and HSS SIMPLE Diameter deployed in our WSN/IMS integrated environment. SIP Game client (deployed on PROTOTYPE ARCHITECTURE phone) and SenseCall client UE (deployed on laptop) The SDS is an Eclipse-based design and execution environment in which IMS applications can Figure 4. The prototype components. be designed, deployed, and tested. One of the features provided by SDS is an IMS simulated environment simulating CSCFs, a home sub- matter for the extraction of information from scriber server (HSS), and an application server received messages and for XML formatting of acting as a container for the deployment of SIP information to be inserted in newly created mes- servlet-based services. Figure 4 illustrates the sages; and they rely on an information/policies different prototype components developed using repository for the storage of the extended PIDF the SDS platform. (used as XML schema), the information access In the prototype the JAIN PS [8] (originally policies, and the contextual information that is relying on a JAIN SIP stack for communication) persistently stored for future notifications. was remodeled as a SIP servlet to enable its deployment in the SDS application server. Fur- thermore, the presence server’s XML schema PROTOTYPE IMPLEMENTATION AND was extended with the additional data elements, ROOF OF ONCEPT PPLICATIONS and its logic was enhanced with the publication P C A trigger mechanism. The server side of the gam- To build a proof-of-concept prototype of our ing application was implemented as a SIP servlet architecture, we used Ericsson’s Service Devel- and deployed in the SDS application server, opment Studio (SDS) [7] as the implementation while the game clients were developed using the platform and extended the existing JAIN pres- SDS IMS client platform and installed on P990 ence server [8] to fit our design. The WSN/IMS Sony Ericsson phones. The server side of Sense GW was implemented from scratch. Further- Call [9] (originally developed as a SIP-based more, to illustrate how new applications can be standalone Java application) was remodeled as a developed using the capabilities of our system, a SIP servlet and ported to SDS. Furthermore, the pervasive game called Fruit Quest and a person- application logic was modified to communicate alized call control application, Sense Call, were with the PS (instead of direct communication developed. In this section we start by giving a with the GW) to obtain the required informa- general description of these two applications, tion. In this prototype two types of sensors were and then discuss the prototype architecture used: MIT Cricket location sensors [10], accessi- before presenting the setups used to test the ble via the Cricket API; and the MTS300/Mica2 application scenarios. environmental sensor [11], accessible via the Crossbow API. PROOF OF CONCEPT APPLICATIONS As for the WSN/IMS GW, it was implement- Fruit Quest is a strategic pervasive game ed as a Java-based extended presence agent rely- designed in our laboratory. In this game, players ing on a Microsoft access database and a set of are assigned plantation zones, in addition to APIs (the JAIN SIP, Cricket, and Crossbow some virtual game objects (e.g., fruits, walls, APIs) in its operation. All of the components of bombs, and virtual money). WSNs are used to the GW were implemented, except for the capa- detect and convey the location of players and bility publication and access control modules, their presence in zones to the network. Players which were omitted for simplicity. physically move between plantation zones within the game area, and as they move, they see the PROTOTYPE SETUPS AND TEST SCENARIOS zones appearing on their terminals and get noti- As shown in Fig. 5a, the Fruit Quest game setup fications about game events. They can also com- consisted of two laptops and three phones, form- municate with each other using IMS instant ing a WLAN, in addition to a set of MIT Cricket messaging. When players are in their plantation location sensors [10]. The game clients ran on zones, they can plant fruits and add defensive the phones, while one of the laptops represented walls for protection. When in rivals’ zones, play- the IMS simulated environment (including the ers can pick fruits and attack the zones using game server) and the other laptop represented bombs. When all defensive walls in a zone are the WSN GW. The following interactions relat- destroyed, the zone can be occupied by rivals. ed to the pervasive gaming scenario were suc- When the time of the game ends, the player with cessfully tested: First, the WSN GW was the highest number of zones and fruits wins the registered in the IMS. Then three players, each game. carrying a phone with an attached Cricket listen-

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er, started moving between three game zones. Cricket beacons mounted to the ceiling were WSN/IMS used in conjunction with the Cricket listeners gateway 4. NOTIFY attached to the phones to determine the location 3. PUBLISH (game_zone_ (game_zone_ change event) / 200 OK change event) of the players. This information was conveyed 2. Event (by Cricket software running on phones) to the detected: game zone WSN GW using TCP/IP communication. The change GW monitored the information received, and IMS simulated environment (CSCFs, when it determined that a player had moved to HSS, extended PS, game server) another game zone, it published this event (using a SIP PUBLISH message) to the extended PS, 5. Game updates which notified (using a SIP NOTIFY message) Area 1 Area 2 Area 3 the game server. This last then sent the appropriate game updates (based on the received 1. Update 1. Update 1. Update Cricket information) to the game clients hosted by the location location location beacons players’ UE, which updated the game display. A similar setup was used for the Sense Call User’s phone User’s phone User’s phone (with attached (with attached (with attached application, as depicted in Fig. 5b. In this case, cricket listener) cricket listener) cricket listener) the application clients were installed on two laptops, while the IMS simulated environment host- (a) ed the server side of the application. The following interactions were then successfully tested: First, the two clients were registered as WSN/IMS 4. NOTIFY IMS users, and the server side of the application gateway 3. PUBLISH (location_ (location_ was used to schedule a call between them. Next, change event) / 200 OK change event) 2. Event the users, carrying their laptops (with attached detected: Cricket listeners), started moving throughout the location 5. Event detected change two users in their office space, and their location information was offices conveyed to the GW. Upon detection of a loca- IMS simulated environment (CSCFs, HSS, tion change, the GW published this event (using extended PS, SenseCall application server) a SIP PUBLISH message) to the PS, which notified the server side of the application (using a 1. Update 1. Update SIP NOTIFY message). When the application location location detected that two users were in their respective 7. INVITE/ offices, it established a third-party controlled call 6. REFER (refer_to: UE2; OK/ACK Cricket between them by sending a SIP REFER message method=invite)/ 8. NOTIFY (refer_event) beacons to one of the users’ UE. This last accepted the User’s laptop User’s laptop referral using a SIP 202 message, then sent a SIP (with attached (with attached INVITE message to UE2. When the call was cricket listener) Room A Room B cricket listener) established successfully, UE1 notified the Sense Call application about the result of the referral (b) event. Figure 5. Prototype setups: a) Fruit Quest game setup; b) Sense Call application PERFORMANCE EVALUATION setup. To evaluate the performance of our system, we used the Fruit Quest prototype to collect some measurements, focusing on the publication inter- was deployed. It should be noted that the game actions (between the GW and the PS) and noti- server’s logic was slightly modified (for testing fication interactions (between the PS and the purposes) to subscribe/accept environmental game server). Spatial (i.e., location) and environ- information from the PS, in addition to the loca- mental (i.e., light/temp) data was collected, and tion information it originally used. Furthermore, two performance metrics were used: the three Sony Ericsson P990 phones, with attached response time (in milliseconds) and the network Cricket listeners and running the Symbian oper- load (in bytes). ating system and the IMS client platform (pro- In addition to the sensors, the testbed con- vided with SDS), hosted the game clients. Table sisted of the following: the GW, running on a 1 shows some of the measurements collected Pentium 4/2.5 GHz laptop, with 512 Mbytes using this testbed. These values are average RAM and Windows XP. This laptop was con- measurements over 20 trials. nected with an MIB510 sink node, allowing it to In the measurements displayed in Table 1, communicate and collect data from sensor nodes the response time for proactive publications is — this data being monitored using a MoteView calculated at the GW level as the time duration application installed on the laptop. A second between the moment when information is laptop with a similar configuration (i.e., 1.6 GHz accessed by the GW’s publisher module (from Intel Pentium Duo with 1 Gbyte RAM, running the information repository) and the message is Windows XP) hosted the IMS simulated envi- created/sent, until a successful publication ronment (the CSCFs, HSS, and extended PS), response is received from the PS. For reactive while a third laptop with an identical configura- publications, the response time (also measured tion hosted a second instance of the IMS envi- at the GW level) is calculated from the moment ronment in which the Fruit Quest game server a publication trigger (i.e., a SIP OPTIONS mes-

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than location-information-related interactions Response time Network load Operation Scenario (e.g., a decrease of 27 ms and 72 bytes for proac- (ms) (bytes) tive-environmental publication in comparison to proactive-location publication). This is because Proactive-location the number of XML fields/tags required to rep- 205 1139 information resent location information is larger than what is needed to model environmental data, thus Proactive-environ- requiring more time for XML formatting and 178 1067 mental information generating bigger message payloads. The performance of location-information-related interac- Publication tions could therefore be improved by using Reactive-location 228 2371 another modeling schema that requires a smaller information number of tags for the representation of this type of information. Reactive-environ- 214 2300 mental information RELATED WORK AND Location LESSONS LEARNED 224 1335 information Notification Several solutions have been proposed for the Environmental integration of WSNs in the Internet, while few 164 1241 information others have investigated their integration with 3G networks. In this section, we discuss the solu- Table 1. Network load and response time measurements. tions that are the most relevant to our work. The e-SENSE architecture [12] aims at making ambient intelligence available to beyond 3G sage) is received from the PS, acknowledged and networks to enhance their service provisioning responded to by a PUBLISH message, until a capabilities. This solution focuses on information successful publication response is returned by acquisition aspects by defining the protocol stack the PS. As for notifications, the response time is to be implemented by sensor nodes as well as a measured at the PS, from the moment the infor- reference model for the WSN GW, but it does mation is internally accessed and the message is not address issues related to information man- created/sent, until a successful notification agement in the core network. Moreover, the response is received from the game server. proposed GW model is generic and does not Several types of comparative analysis were take into consideration IMS-specific require- made by examining the collected measurements, ments for WSN/3G integration. two of which are presented here. The first analy- TinyREST [13] and TinySIP [14] are solu- sis was made by comparing the performance of tions for WSN/Internet integration. Both solu- the two modes of publication for the same type tions propose the use of application-level GWs of information (e.g., proactive location vs. reac- to enable the exchange of information between tive location), in order to calculate the overhead WSNs and Internet clients. Although these solu- introduced in the case of the reactive mode. This tions rely on standard IP protocols (i.e., HTTP overhead is caused by the exchange of an addi- and SIP), they employ standalone GWs that are tional pair of SIP messages (i.e., OPTIONS and built to be used directly by end users’ applica- OK messages) to trigger the publication, and by tions and cannot be integrated in the IMS to the processing of the publication triggers con- leverage its other capabilities. The same limita- tained in the OPTIONS message body. The aver- tion applies to the web-service-based GW [9] age overhead, in terms of response time, ranges previously developed in our laboratory. between 23 ms (for location info) and 36 ms (for During the course of this project, we learned environmental info) per operation, which can be several important lessons. The first is that the considered non-significant, since its effect will introduction of a sensor GW and an extended barely be felt by the end user. The penalty in PS in the IMS architecture enables the availabil- terms of network load is nevertheless significant ity of additional contextual information in the (an increase of 1.2 kbytes/operation, for both network. For instance, in our prototype, two types of information). However, this penalty will additional types of information were made avail- only be incurred occasionally since the reactive able in the IMS: high-precision location informa- mode is a secondary mode of operation only tion provided by Cricket sensors (e.g., the ID of used when the required contextual information a room in a building) — information that consti- is not available (or is not fresh enough) in the tutes a refinement of the location information network. currently supported in mobile networks (mainly By comparing the performance of one mode low-precision cell ID information); and environ- of publication for two different types of informa- mental data provided by the MTS300/Mica2 tion (e.g., proactive location vs. proactive envi- environmental sensor — information that is cur- ronmental), we can see how the type of rently unavailable in a standalone IMS. Addi- information exchanged can affect the perfor- tional types of information could also be mance. The same type of comparison can be supported by integrating other types of sensors, made for notifications of different types of infor- such as the Zephyr BioHarness system providing mation. In general, we notice that the publica- physiological and activity-related information. tions/notifications of environmental data achieve Another lesson we learned while implement- better response times and induce lighter loads ing the GW is that the development of systems

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that interact with heterogeneous sensors coming would have been required if we had to learn how from different vendors is challenging. In our to deal with other types of sensors. However, It is important to case, our WSN/IMS GW interacted with location porting this application to our WSN/IMS inte- and environmental sensors using two proprietary grated environment, by replacing the original mention that the use interaction mechanisms (i.e., the MIT Cricket information acquisition logic with standard SIM- of SDS requires basic API and the Crossbow platform), and had to PLE-based interactions with the PS, only took us knowledge of the map their sensor-specific data into an abstract one day — with the observation that minimal format before transforming it into XML docu- effort would be required for the collection of IMS operation and ments that are published using SIP in the 3G additional types of information from the PS, offers a low level of network. Therefore, the interaction with addi- since the same logic could be reused. tional types of sensors would require modifica- Finally, the availability of IMS development abstraction in tions/additions to the GW logic (mainly the toolkits is essential for the development and relation to its WSN interface and the information acquisition testing of IMS-related prototypes and applica- configuration, the module) each time a new sensor type is consid- tions. However, the choices of freely available ered. This is due to the lack of a unified stan- toolkits are limited to Ericsson’s SDS and the provisioning of users, dard API enabling interaction with various open source IMS core (OSIMS) [16] developed and the technology sensors. An initiative that may solve this issue is by Focus. Unlike the OSIMS, which only offers the Zigbee standard [15], which aims at achiev- some of the IMS core nodes (i.e., CSCFs and supported for the ing interoperability between sensor nodes as well an HSS), SDS provides a more comprehensive development of as sensors and sinks, by defining a common pro- design and test environment by also offering an server-side tocol stack to be supported by all vendors. Cur- integrated development environment, a set of rently, the Zigbee standard has specified the service APIs facilitating the development of applications. protocol layers up to the transport level — the client/server side applications, an IMS terminal application layer, however, remains to be emulator, an automated testing framework, defined. We should also note that the modulari- and a presence group management (PGM) ty of our GW design helps to minimize this module. impact by limiting to two the number of modules Despite its attractive features, SDS does have that will be affected (by the change of the target- some limitations, the first being its lack of exten- ed sensor). sibility. In fact, since this toolkit is not open Another lesson related to the implementation source, it was not possible to extend its PGM of the extended presence server is that there are module, which obliged us to use an external PS only a relatively small number of SIMPLE-based and remodel it according to the SIP servlet tech- open source presence servers. In this project we nology in order to deploy it in SDS. Further- chose the JAIN PS since it is easily extendible more, SDS did not support all the IMS and is based on the popular JAIN SIP stack with functionalities we needed; for instance, implicit which we were familiar from other projects. registration of identities was not supported by its However, like the other open source servers, provisioning environment. Finally, it is important the JAIN server does not implement advanced to mention that the use of SDS requires basic presence functionalities such as partial publica- knowledge of the IMS operation and offers a tions/notifications and event notification filters. low level of abstraction in relation to its configu- Furthermore, its design suffers from tight cou- ration, the provisioning of users, and the tech- pling between the presence server functionality nology supported for the development of and the SIP proxy/registrar functionalities, which server-side applications (i.e., the SIP servlet are all bundled together. This resulted in dupli- technology). This is certainly a roadblock to cate functionality when this server was deployed speedy application development, independent of in SDS. For example, IMS users had to be regis- the type of applications involved. tered twice, once to the CSCF and again to the PS. REFERENCES In relation to applications development, we [1] G. Camarillo and M. Garcia-Martin, The 3G IP Multime- also learned that the introduction of context as dia Subsystem, Wiley, Aug. 2004. an application building block in the IMS facili- [2] I. Akyildiz et al., “Wireless Sensor Networks: A Survey,” IEEE Commun. Mag., Aug. 2002. tates the development of novel context-aware [3] M. El Barachi et al., “A Presence-Based Architecture for value-added services. In fact, the functional sep- the Integration of the Sensing Capabilities of Wireless aration between context management operations Sensor Networks in the IP Multimedia Subsystem,” IEEE and the logic of the applications (using the con- WCNC ‘08, Las Vegas, NV, Mar. 2008. [4] J. Rosenberg, “The XML Configuration Access Protocol textual information) enables the reuse of com- (XCAP),” IETF RFC 4825, May 2007. mon mechanisms and concepts by different [5] SIMPLE Working Group, “SIP for Instant Messaging and applications, and abstracts developers from the Presence Leveraging Extensions (SIMPLE)”; http://www. complexities of context acquisition/management ietf.org/html.charters/simple-charter.html [6] K. Aberer, M. Hauswirth, and A. Salehi, “A Middleware for operations (e.g., the interaction with sensors Fast and Flexible Sensor Network Deployment,” 32nd Int’l. using proprietary APIs, and the processing of Conf. Very Large Databases, Seoul, Korea, 2006. the collected low-level information), thus speed- [7] “Ericsson Service Development Studio 3.1 — Technical ing the application development process. This is Product Description,” Feb. 2006; http://www.ericsson. evidenced by the fact that the initial version of com/mobilityworld/developerszonedown/downloads/ ______docs/ims_poc/SDS_technical_description.pdf the game, which was designed to directly com- [8] JAIN-SIP-PRESENCE-PROXY; http://www-x.antd.nist.gov/ municate with sensors (in the initial phase of the ______proj/iptel/nist-sip-downloads.html project), required close to two weeks for the [9] T. Ta et al., “Using Web Services for Bridging End User implementation of the logic related to sensory Applications and Wireless Sensor Networks,” IEEE ISCC ‘06, Sardinia, Italy, June 2006. information acquisition from the Cricket sensors, [10] A. Smith et al., “Tracking Moving Devices with the with which we were not familiar. Additional time Cricket Location System,” MOBISYS, Boston, MA, 2004.

IEEE Communications Magazine • April 2010 49

[11] MTS300 Sensor; http://www.xbow.com/Products/ ROCH H. GLITHO [SM] holds a Ph.D. (Tekn.Dr.) in tele-infor- ______productsdetails.aspx?sid=75 matics (Royal Institute of Technology, Stockholm, Sweden) [12] A. Gluhak et al., “e-SENSE Reference Model for Sensor and M.Sc. degrees in business economics (University of Networks in B3G Mobile Communication Systems,” Grenoble, France), pure mathematics (University of Geneva, 15th IST Summit, 2006. Switzerland), and computer science (University of Geneva). [13] T. Luckenbach et al., “TinyREST: A Protocol for Inte- He works in Montreal, Canada, as associate professor at grating Sensor Networks into the Internet,” REALWSN ETS, University of Quebec, and as adjunct associate profes- ‘05, Sweden, 2005. sor at CIISE, Concordia University. He has held several [14] S. Krishnamurthy, “TinySIP: Providing Seamless Access senior technical positions (e.g., expert, senior specialist) at to Sensor-based Services,” MOBIQUITOUS ‘06, San Jose, Ericsson Canada and Ericsson Sweden. He has also served CA, 2006. as Editor-In-Chief of two IEEE Communications Society [15] Zigbee Alliance, “Zigbee Specification 1.0,” June 2005; magazines: IEEE Communications Magazine and IEEE Com- http://www.zigbee.org/en/index.asp munications Surveys & Tutorials. (http://www.ece.concor-______[16] Open IMS Core; http://www.openimscore.org/ ______dia.ca/~glitho/)

FERHAT KHENDEK received a Bachelor’s degree in computer BIOGRAPHIES engineering, option software, from the University of Tizi- Ouzou, Algeria, and M.Sc. and Ph.D. degrees in computer MAY EL BARACHI ([email protected])______holds a Ph.D. and a Master’s degree in electrical and computer engineer- science from Université de Montréal. He is a professor with ing from Concordia University, Canada, and a Bachelor’s the Electrical and Computer Engineering Department of degree in electronics and telecommunications engineering Concordia University. From 2001 to 2002, and from 2008 from the Arab Academy for Science and Technology, to 2009, he was a visiting researcher with Ericsson Research Egypt. She carried out her Master’s and doctoral research Canada in Montreal. He has published more than 120 ref- as part of an industry/academia cooperation program ereed research papers in journals and conference proceed- established between Ericsson Research Canada and Concor- ings. His research interests are mainly in the design, dia University. She was also part of the IST Ambient Net- modeling, and analysis of real-time software systems, high works project — a European Union (EU) 6th framework service availability, and value-added service engineering for project. Presently, she is a postdoctoral fellow at the Uni- next-generation networks. versity of Quebec School of Superior Technology (ETS). Her current research interests include service engineering, qual- RACHIDA DSSOULI received a Doctorat d’Université degree ity of service and adaptive resource management, context in computer science from the Université Paul-Sabatier of awareness, virtual networks, and next-generation networks. Toulouse, France, in 1981, and a Ph.D. degree in computer science in 1987 from the University of Montréal. ARIF VALI KADIWAL received a B.S. degree in computer engi- She is a professor with the Electrical and Computer Engi- neering from Sir Syed University of Engineering and Tech- neering Department of Concordia University and with the nology, Pakistan, in 2003 and an M.S. degree in electrical College of Information Technology of the United Arab and computer engineering from Concordia University in Emirates University. She spent a sabbatical year 2009. He worked at the Telecommunication Service Engi- (1995–1996) at Nortel and was a visiting professor at neering Laboratory, a joint research laboratory between Abu Dhabi University, United Arab Emirates, from 2008 Ericsson and Concordia University, from 2007 to 2008. His to 2009. Her research area is communication protocol work was concentrated in the area of the IP multimedia engineering, requirements engineering, and multimedia subsystem and wireless sensor networks. applications.

50 IEEE Communications Magazine • April 2010

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TOPICS IN DESIGN &IMPLEMENTATION Broadband Internet in EU Countries: Limits to Growth

Ryszard Struzak, National Institute of Telecommunications

ABSTRACT percent (uniform across the whole EU) by the year 2010 and higher percentages in later years This article provides an analysis of broadband [2]. The project is well advanced and statistical Internet diffusion in 27 countries of the Euro- data indicate that every EU country has been pean Union. It proposes a simple model of its progressing fast. In spite of that success, the growth and identifies the theoretical growth lim- gaps between countries still exist, and in some its in each country. Some aspects of the Euro- cases they have increased during the project pean i2010 project implementation are lifetime. presented, discussed, and compared with the Will the gaps ever vanish? As the raw statisti- model. Comments on bottlenecks and major bar- cal data do not directly answer this intriguing riers in the broadband Internet diffusion process question, this article proposes a simple approach are also offered. The existing digital gaps are that leads to a reasonable answer. The article is irreducible in some cases and will exist as long as organized as follows. The next two sections pre- the current development conditions continue. sent the approach used. A mathematical model The approach and analysis method proposed is proposed to infer intrinsic limits of the pene- here may be useful in examining limits of other tration rates in various countries and user services or in other regions during the planning, groups. Once the limits are known, it is straight- design, implementation, and performance track- forward to determine whether or not the gap ing stages of existing or new services. between two given countries or user groups will vanish and to answer the question. NTRODUCTION The limits are calculated for each of the 27 I EU countries, and compared with the actual penetration rate and the i2010 target. Some bar- Broadband Internet popularity is not uniform riers to broadband diffusion are discussed. and there are significant gaps or divides among Efforts required to reach the i2010 target are countries, regions, social groups, and so on. That evaluated and compared among countries to popularity is often expressed in terms of the infer possible bottlenecks. For that purpose, two number of broadband access lines per 100 inhab- indices, the market index and effort index, are itants, known as the penetration rate. The per- proposed. centage of households with broadband Internet The article extends earlier work [3]. The pre- access and percentage of enterprises with such sented approach is generic and may be applied access are other metrics of the popularity. to other regions outside the EU and to other These disproportions (digital gaps) constitute services in the telecommunications space. It may an open issue for both developed and develop- be useful when assessing the business viability of ing countries, and various projects have been ini- a new or existing service, and when tracking the tiated around the world to reduce them. The business performance of a service after deploy- European Union (EU), for instance, has ment. launched its i2010 project [1]. The EU is an economic and political union of 27 member states ODELING offering the free movement of people, goods, M services, and capital. It represents about 500 mil- From time immemorial, people have wanted to lion citizens and 22 percent of the gross world know the future. Earlier, they consulted oracles product. and magic omens, but today they use mathemati- The EU countries differ significantly in size, cal models that are based on data, which repre- development degree, and wealth. For instance, sent the process under consideration. Having the the gross domestic product purchasing power data, one selects an appropriate mathematical parity per capita (GDP PPP) is $81,200 in Lux- function and matches it to the data. With such a embourg and $12,900 in Bulgaria. Large differ- function, one can calculate (interpolate or ences also exist between geographical regions extrapolate) new data, outside the original set of and between social strata in some countries. known (measured) data. The aim of the i2010 project is to complete The model presented below is proposed not the Single European Information Space. The to make specific predictions, but to explore and target is a broadband penetration rate of 90 understand better how the broadband Internet

penetration rate grows with time. That idea is somewhat borrowed from The Limits to Growth, 100% a famous book by Donella H. Meadows and her MIT colleagues, as the title of this writing indi- 1 cates. The growth of the Information Society and Internet diffusion can be compared to a course of virtual illness, where infected people become 2 Internet users. In case of real diseases we would like to be all 100 percent immune; hence vacci- nations and other preventive measures. With Internet diffusion the aim of governmental poli- 3 cies is quite the opposite — 100 percent of the population infected; hence i2010 and similar pro- 50% jects. In studying diseases differential equations 4 have been successfully used [4], but such an approach cannot be applied here because of the lack of necessary data. Data used in this article are the yearly statistics collected by Eurostat, the Statistical Office of the European Communities [5]. For each data set a logistic growth function is constructed in the form a 5 yt()= . 1+++expbcdt() (1) 0% 2000 2005 2010 2015 Here y is the penetration rate of broadband Year Internet access (or percentage of households/ enterprises with such access) at time t. Constants Figure 1. Diffusion of broadband Internet in Poland for various user groups. 1: a, b, c, and d are time-independent growth percentage of large enterprises (>250 employees) with broadband Internet; 2: parameters: a is the growth limit, and b, c, and d the same for enterprises with 50 to 249 employees; 3: the same for enterprises are the time-scaling factors. These represent the with 10 to 49 employees; 4: percentage of households with broadband Internet; collective effect of all factors (economic, techno- 5: penetration rate (the number of broadband access lines per 100 inhabi- logical, social, etc.) that influence the diffusion tants). The points represent the observation data [5], and lines the results of process. Their numerical values are determined author's calculations following Eq. 1. The limits (asymptotes) of lines 3, 4, using the method of least squares fitting to the and 5 are noticeable after 2012. measured data in hand. This forces the plot of the growth function y(t) to pass as close to every data point as possible. As the function contains four unknown growth parameters, the data set that it fits the data in hand well. One should should contain not less than four data points. mention, however, that some researchers use Otherwise, the values of some parameters have more sophisticated models; the interested reader to be assumed. is referred to R&D report [7]. The popularity of broadband Internet increas- In determining the model parameters, one es from year to year. Each time a new data point can impose additional constraints on the logistic is taken into account in the model, the growth function. Indeed, in a few cases, when the calcu- parameters are to be determined anew, and the lated trend line tended to exceed 100 percent, future growth path including the growth limit we added an arbitrary requirement that it must may change slightly. The limit becomes a moving not surpass that percentage. limit, per analogy to moving average known from statistics. EXAMPLES: DISCUSSION IMITS ELAYS AND APS There are no ideal models; potential sources of L , D , G modeling errors are [6]: Due to limited space, it is impractical to exam- • The model fails to include significant vari- ine every EU country here; therefore, only ables. three countries are presented as examples; sim- • The model includes superfluous variables. ilar patterns are observed in other countries. • The model uses wrong data. These countries are Poland, Romania, and • The model assumes the wrong function. Estonia. Poland is the sixth largest country in The first two items do not apply here because the EU in terms of population size, GDP, and the model is descriptive and does not touch the area. Its population is 38.1 million, the GDP cause-effect relations. per capita is 58 percent of the EU average, and The data concern the broadband Internet, the Human Development Index (HDI) equals but broadband represents various numerical val- 0.880. The population of Romania is 21.5 mil- ues in various countries [5], and this may influ- lion, its GDP per capita reaches 46 percent of ence comparisons among countries. With respect the EU average, and the HDI is 0.837. The to the last item from the list above, Eq. 1 is population of Estonia is 1.3 Mmillion, its GDP quite appropriate, and the figures below show per capita amounts to 68 percent of the EU

IEEE Communications Magazine • April 2010 53

ees) it is at 77 percent, and for small enterprises 100% (10 to 49 employees) at 53 percent. For house- 1 holds, the penetration limit is the lowest and equals 51 percent. Once the growth limits are known, it is 2 straightforward to determine whether the digital gap between two given user groups or countries will vanish, or not. The gap, 6y(t), is defined as the difference between two growth functions, y1 3 and y2, at a given reference time t. For instance, in Fig. 1 the gap between lines 3 and 2 in 2005 reaches 30 percentage points or so. In this exam- 50% 4 ple the lines do not converge; the process that started at a lower level remains always delayed, and the gap remains forever: it is irreducible. However, in the case of lines 3 and 4, the gap 5 first increases (up to 2006 or so) and then decreases asymptotically. Generally, the gap varies until it reaches its 6 asymptotic value. It vanishes only if the two growth lines have a common limit. As the growth lines approach the limit asymptotically, the process of closing the gap takes a long time, theo- retically infinite. 0% The irreducible gap is the limit to which the 2000 2005 2010 2015 gap 6y approaches when time tends to infinity. It | is easy to notice that it equals the difference a1 | Figure 2. Broadband Internet diffusion in Estonia (continuous lines) and – a2 , where indices 1 and 2 differentiate between Romania (dashed lines). 1 and 2: percentage of large enterprises connected to the growth lines, and a has been introduced in a broadband network; 3 and 4: percentage of households connected to a Eq. 1. For instance, in the figure the irreducible broadband network; 5 and 6: the penetration rate of broadband. The points gap between 1 and 3 is about 40 percentage represent the observation data [5], and lines the results of author's calcula- points. tions following Eq. 1. FURTHER EXAMPLES Figure 2 compares the growth of broadband average, and the HDI is 0.883. As concerns the Internet popularity in two other EU countries, broadband Internet penetration rate, Poland Estonia and Romania. (To make the figure read- ranks 26th, Romania 23rd, and Estonia 10th able, only two user groups are shown: house- among the EU countries. holds and large enterprises.) For large enterprises in Estonia, the limit LIMITS exceeds 95 percent, whereas in Romania it is Figure 1 illustrates the diffusion process of lower, about 75 percent. For households in broadband Internet in Poland. The figure com- Estonia the limit is about 65 percent; in Roma- pares the growth of Internet diffusion in enter- nia it is also lower, about 25 percent. In spite of prises and households. At first glance data series these differences, the penetration rates (that 3, 4, and 5 seem to grow without limits, and only merge households and enterprises) in both application of Eq. 1 makes it possible to infer countries tend to the same limit of about 25 their limits. The percentages of households and percent. small enterprises with broadband Internet exhib- it the lowest limits; the same relations are DISCUSSION observed in all countries. In the long term, each and every household will have broadband access to the Internet, as we all DELAYS wish. Consequently, it appears that the ultimate Figure 1 shows that the growth lines are delayed limit for the percentage of households with relative to one other. By definition, the delay Internet access should be 100 percent. However, 6t(y) is the time difference between the two lines it is difficult to reach such a high limit, as there at a given growth level y. It can be determined are people immune to the Internet, afraid of graphically or using function t(y), the inverse cybercrime, or those below the poverty line (we function for y(t) from Eq. 1. For example, the will come back to these issues later on). delay of line 3 relative to line 2 at the level of 50 The authors of [7], for instance, account for percent is about four years. Note, however, that this fact by assuming the limit (they call it satu- the delay cannot be determined for levels above ration level) of broadband Internet penetration 60 percent. The reason is that line 3 does not rate at 20 percent for Poland and 55 percent for reach such high values: its growth limit is lower. France. At the time of their study, broadband services in the EU were at an early phase, and GAPS the diffusion data were scarce, so they had to Figure 1 illustrates the degree of digital divide assume some values. In contrast, in this article among various user groups. For large enterprises the limiting values below 100 percent result (> 250 employees) the percentage limit is at 94 from the actual data on broadband Internet dif- percent. For medium ones (50 to 249 employ- fusion [5].

54 IEEE Communications Magazine • April 2010

In the future, with the mass applications of the broadband Internet of Things, the limit may 0% 10% 20% 30% 40% 50% surpass 100 percent, as has already happened Malta with the telephone penetration rate in some countries. Sweden

THE I2010 PROJECT Germany

The theoretical limits, calculated for each of the Denmark 27 EU countries, are presented in Fig. 3, together with the actual penetration rates for each EU Finland country. These limits are expected to be reached in the long-term perspective if the present devel- Hungary opment conditions continue in each country without change. The limits are the highest in Malta, Netherlands Sweden, Germany, and Denmark, but even there they are well below 90 percent, the i2010 target; Norway the actual penetration rates are even lower. This indicates that the i2010 target of 90 per- Belgium cent penetration rate, uniform across the whole EU, may not be reached easily. Reaching it United Kingdom requires significant efforts; we will come back to that issue later on. Estonia

BARRIERS Luxembourg It follows from Fig. 3 that a significant part of the population in the European Union does not France fully participate in the Information Society. This will continue as long as the present Internet Spain development conditions do not change. Migra- Cyprus tion to broadband Internet in urban areas and large enterprises is developing well. It is, howev- Romania er, delayed in small enterprises, households, and especially in rural areas where a large part of a Ireland country’s population lives. The European Commission comments on this Austria as follows: “Despite the general increase in broadband con- Slovenia nectivity, access in more remote and rural regions is limited because of high costs due to low density of Bulgaria population and remoteness. Population scarcity limits the exploitation of economies of scale, entails Latvia lower rates of demand and reduced expected returns from investment. Remoteness often implies the need Italy of bridging longer distances from the local exchanges to the premises and to the backbone. Portugal Commercial incentives to invest in broadband deployment in these areas often turn out to be Lithuania insufficient. On the positive side, technological innovation is reducing deployment costs.” [8] Czech Republic In line with these comments, the EU Com- mission recently proposed an extra €1 billion in Poland aid to stimulate the spread of broadband Inter- net [9]. Slovakia There are numerous reasons for such dispro- Penetration rate 2007 portions, and they may be different in each Greece Limit to growth country. These may be cultural, language, dis- 0% 10% 20% 30% 40% 50% ability, age, and gender barriers, lack of skills, precarious economic conditions, and so on. An Figure 3. The current diffusion limits in the EU countries (author's calculations EU survey has identified the major reasons cited following Eq. 1) compared with the actual (2007) penetration rate of broad- for not having broadband Internet at home. The band Internet. Source of the penetration data: [5]. most significant are: “not needed or not wanted,” “too high costs,” “lack of skills,” and “privacy or security concerns” [5]. The first one was indicated by about 50 percent of responders. another hierarchy of needs and values, and does not know, does not understand, and/or does not TASKS appreciate the benefits such access can offer. The fact that half of the people surveyed do not Bottlenecks are households and small enterpris- need or want broadband access at home may es in rural areas and poor social strata. To indicate that a significant part of society has change this attitude, additional stimulus pro-

IEEE Communications Magazine • April 2010 55

grams and resources (effort, capital, etc.) are • Technology area (cheap/free software and required. Favorable conditions need to be creat- inexpensive hardware) ed in various areas [3]: • Organization area • Content area (to address the real needs of small enterprises and rural communities) QUANTIFYING EFFORTS • Education/promotion area (to educate citi- The creation of the single European informa- zens at all levels, stimulate involvement of tion space means significant efforts must be local communities) made in each European country, and each • Investment area (public/governmental infra- country’s position is specific. At first glance it structure sharing) seems that countries in which the current pene- • Legal/regulatory area (remove legal barri- tration rate is the lowest confront the greatest ers; encourage new business models; com- effort to reach the i2010 target. However, that petition, investments, and sharing effort is to be measured not in terms of the infrastructures; facilitate fiscal conditions; penetration rate but in terms of the increase of broadband access as universal service; solve the broadband subscriber base required to issues of spectrum access and intellectual reach the target. property rights) To quantify that effort, we propose the mar- • Business area (public aid; new business ket index, defined as the product of the coun- models) try’s population and the required increase in the actual penetration rate to reach the 90 percent target. It is the potential market size 0% 5% 10% 15% 20% induced by the i2010 project (the size of the new subscribed base to be created). In Fig. 4 it Germany is normalized in such a way that 100 percent Italy represents the whole European Union. Seven countries (Germany, Italy, France, United France Kingdom, Spain, Poland, and Romania), represent a major part of the new subscribers part of United Kingdom the i2010 target. Spain QUANTIFYING BOTTLENECKS Poland The EU countries differ not only in the market Romania size mentioned above, but also in wealth, or the GDP (PPP) per capita, and these two factors Netherlands play major roles in ensuring uniform broadband Greece Internet penetration. Efforts needed to reach the i2010 target increase with the size of the Portugal base of new broadband subscribers and decreases with the country’s GDP: the greater the sub- Czech Republic scribers’ base to be created and the lower the Hungary GDP, the greater the efforts. To make reasonable comparisons among the EU countries in Belgium this aspect, an effort index is proposed. It is Bulgaria defined as the ratio of the market index to the GDP (PPP) per capita. It is shown in Fig. 5 for Austria each EU country. Sweden Bottlenecks are to be expected to materialize in poor social strata, rural, areas and small Slovakia enterprises in countries facing the greatest efforts. These need special attention to avoid Finland significant delays in reaching the i2010 target. Denmark Figure 5 indicates that seven countries (Poland, Germany, Romania, Italy, Spain, United King- Ireland dom, and France) are facing the greatest Lithuania efforts; consequently, they require special assistance. A question arises on how to allocate that Latvia aid to lower the probability of major bottle- Slovenia necks before they materialize. A rational guide would be to distribute it proportionally to the Estonia effort index. Cyprus CONCLUSIONS Luxembourg The model proposed here matches the historical Malta data well. It infers intrinsic limits to growth of 0% 5% 10% 15% 20% the broadband Internet penetration rate that may be unnoticeable otherwise. These growth Figure 4. Market index — increase of broadband subscriber base required in limits depend on many factors. Rural and poor each EU country to reach the i2010 target; European Union = 100 percent. regions and small enterprises are major bottle- (Author's calculations.) necks.

56 IEEE Communications Magazine • April 2010

The model does not confirm that the existing disproportions in broadband Internet penetra- 0%5% 10% 15% tion rates between countries, regions, and user Poland groups vanish with time. They increase and decrease with time and, in some cases, are irre- Germany ducible and will exist as long as the present development conditions continue. This warning Romania calls for a review of our attitude toward reducing Italy the digital divide not only in the European Union but also elsewhere. Spain The i2010 target of 90 percent penetration United Kingdom rate, uniform across the whole EU, may not be reached as quickly as originally expected. This France target requires significant efforts, and some countries/regions require special assistance, such Bulgaria as the recent program [9]. The effort index could Hungary serve as a guide for where that assistance should be directed. Portugal The approach used here to examine Internet Czech Republic diffusion in the European Union may also be applied to non-EU countries as well as to other Greece services besides broadband. Netherlands

ACKNOWLEDGMENTS Slovakia The author would like to thank Juerg Daellen- bach, Sean Moore, Marcin Struzak, and anony- Belgium mous reviewers for their contributions and Austria comments, which have strengthened this text. Sweden EFERENCES R Denmark [1] Commission of the European Communities, “Preparing Europe’s Digital Future: i2010 Mid-Term Review,” Lithuania COM(2008) 199, Apr. 2008. [2] “Opinion of the Committee of the Regions on Bridging Latvia the Broadband Gap and i2010 eGovernment Action Plan (2007/C 146/09),” Official J. EU, June 30, 2007. Finland [3] R. Struzak, “Growth of Broadband Internet in Poland — Models, Trends, and Limits,” Telekomunikacja i Techniki Ireland Informacyjne, vol. 2009, no. 1–2, pp. 38–48, (in Polish); also: R. Struzak, “Broadband Internet Access: Trends Slovenia and Limits,” Proc. 4th BroadBandCom ‘09, Wroclaw, Poland, July 15–18, 2009. Estonia [4] M. Keeling, “The Mathematics of Diseases,” Plus Mag., Mar. 2001, p. 3–8. Cyprus [5] EUROSTAT databases, accessed Mar. 22, 2009; ____http:// ______epp.eurostat.ec.europa.eu Malta [6] R. I. Ackoff, Scientific Method: Optimizing Applied Research Decisions, Wiley, 1962. Luxembourg [7] R. Montagne et al., “Broadband Access Roadmap Based 0% on Market Assessments and Technical-Economic Analy- 5% 10% 15% sis,” BROADWAN, Deliv. D15, 2005. [8] Commission of the European Communities, “Communi- cation from the Commission to the Council, the Euro- Figure 5. Effort index of each EU country to reach the i2010 target. European pean Parliament, the European Economic and Social Union = 100 percent. (Author's calculations.) Committee, and the Committee of the Regions: Bridg- ing The Broadband Gap,” COM(2006) 129, Brussels, Belgium, Mar. 20, 2006. patents. He was the former acting assistant director and [9] European Commission, “Better High-speed Internet head of the Technical Department CCIR-ITU, Editor-in-Chief Access Needed to Revitalise Europe’s Rural Regions,” and Editorial Board Chair of Global Communications, and press rel. no. IP/09/343, EU Brussels, Mar. 3, 2009. a consultant to ITU, UN-OCHA, WB, IUCAF, and other entities. He is co-founder and former Chair of the Internation- BIOGRAPHY al Wroclaw Symposium on EMC. He was elected to leading positions in ITU-RRB, CCIR, URSI, and CISPR. He is the RYSZARD STRUZAK [LF] ([email protected])______is a full professor recipient of the ITU Silver Medal, two International Sym- at the National Institute of Telecommunications, Poland, posia awards, and national awards and decorations. He is and Wroclaw University of Technology, and co-director of a member of the New York Academy of Science and an the ICTP School Series on Wireless Networking. He is the Academician of the International Telecommunication author/co-author of some 200 publications and 10 Academy.

IEEE Communications Magazine • April 2010 57

TOPICS IN DESIGN & IMPLEMENTATION Service Traffic Management System for Multiservice IP Networks: Lessons Learned and Applications

JungYul Choi, Seung-Hoon Kwak, Mi-Jeong Lim, Taeil Chae, Byoung-Kwon Shim, and Jae-Hyoung Yoo, KT Corporation

ABSTRACT tocol television (IPTV) and fixed mobile convergence (FMC) is expected to offer new added Next-generation networks offer new opportu- value to ISPs and opportunities to service pro- nities and challenges to Internet service providers. This is because the next-generation net- viders as well as providers of other online work (NGN) environment now enables the services. Service providers can now deploy new provision of a variety of new services over IP- services over an IP network infrastructure with- based transport networks by utilizing network out building their own networks. In an open net- and service control platforms without building a work environment, the network resources of separate network for each service [1, 2]. This is ISPs should be fairly open to third parties that the fruit of the realization of the NGN environ- plan to launch their own services over the net- ment, which can pave a new way to profitable work. To actively respond to the changing net- network operation. work paradigm, it is essential to measure the In this context, an exact cost accounting of traffic of individual services, and to estimate individual services is essential for ISPs that pro- their cost for cost accounting between service vide services over their own network, as well as provider and ISP. However, current traffic mea- for service providers that utilize open networks surement techniques only provide the total traf- for service provisioning. Cost accounting of indi- fic volume in links, without reporting the vidual services in network building and opera- operator whose services flow through the links. tion will be the basis for the settlement of Some commercial products can classify traffic accounts between ISPs and service providers, or into each application at a specific spot, but we between business departments and a network should install monitoring systems at every spot operating department in an ISP. Accordingly, we throughout the entire network in order to should measure and analyze the traffic volume observe which service traffic flows in every link. of individual service flows in every link over the To satisfy the requirements of the NGN environ- entire network. User behavior in the use of ser- ment, we developed the Service Traffic Manage- vices and traffic characteristics of services should ment System that can analyze the traffic of also be examined and utilized in network design individual services based on user log data. STMS and planning. can report not only the traffic of individual ser- However, legacy traffic measurement tech- vices in every link, but also user behavior for niques simply provide the total traffic volume in each service. In addition, this article shares our links, without reporting which service traffic experience of STMS development. We also flows through the links [3, 4]. It does not report introduce how we utilize STMS in IP network on user behavior in the use of services, nor does design, and discuss business and management it report the traffic characteristics of services. support. Recent commercial products can classify traffic into each application and provide detailed traffic INTRODUCTION characteristics [5, 6]. Deep packet inspection (DPI)-based traffic analysis can provide applica- Each year Internet service providers (ISPs), tion-level contents of traffic by inspecting the which own large-scale network infrastructure, payload of each packet [7]. However, application pump a great deal of money into building their of DPI-based techniques should be carefully networks in order to sustain soaring Internet applied in large ISPs for protecting personal pri- traffic. The explosive increase in Internet traffic, vacy and network neutrality [8]. These solutions which is mostly due to peer-to-peer services and give benefits in providing detailed application- free-rider services, places a huge burden on level traffic classification, but have limited scala- ISPs, with little resulting revenue from their bility and high cost. We should install such traffic network investment. On the other hand, the monitoring systems at every spot throughout the emergence of new services such as Internet Pro- entire network in order to exactly measure the

VoD servers To address this limitation of legacy traffic measurement techniques, we IPTV developed a new IP core network Head-end Access center traffic management network system that can VoIP Access Core classify individual edge router edge router service traffic in links over the entire Internet network, and access IPTV VOD analyze user behav- IPTV multicast ior in the use of VoIP services with high Internet economic benefit.

Figure 1. Multiservice IP network environment.

traffic volume of individual services and where STMS they flow [9]. Thus, to address the changed open network environment for NGN, there is a As shown in Fig. 1, diverse service traffic flows demand to develop a service traffic management over IP networks, and a single link can hold system for achieving the following goals: multiple different types of service traffic. Legacy • Can it measure the traffic volume of indi- traffic measurement systems can only collect vidual service flows in every link over the data on incoming/outgoing traffic at network entire network and where they flow? equipment using Simple Network Management • Can it provide an economic solution that Protocol (SNMP) [3], and analyze flow-level does not require traffic monitoring systems traffic [4, 10] or application-level traffic [7]. at each spot? While these systems are useful in analyzing • Can it provide user behavior data in the use packet, flow, or application-level traffic, they can of services in links and regions? place a big burden on ISPs if there is the need • Can it provide basic data for estimating cost to establish them in every link for precise service accounting of each service provisioned in traffic management throughout the entire net- an open network environment? work. To address this limitation of legacy traffic • Can it provide basic data for an IP network measurement techniques, we developed a new design and planning reflecting the charac- traffic management system that can classify indi- teristics of individual service traffic in spe- vidual service traffic in links over the entire net- cific regions? work, and analyze user behavior in the use of These goals accord with the requirements of services with high economic benefit. STMS can Korea Telecom (KT) to do internal trading analyze services that require authentication pro- between business departments and the network cesses and generate user log data such as IPTV operating department in our Company-in-Com- video on demand (VOD), IPTV real-time chan- pany system. The open network environment has nel type, and Session Initiation Protocol (SIP)- similar issues in cost accounting to those when based VoIP. dealing with two separate companies. To respond to the changing network environment, and uti- STRUCTURE AND FUNCTIONS OF STMS lize network design and business support, we The structure and function blocks of STMS are developed the Service Traffic Management Sys- illustrated in Fig. 2. STMS has a three-tier archi- tem (STMS). A unique feature of STMS that tecture. A collecting server linked with network differentiates it from legacy traffic management management systems (NMS) gathers source systems relying on passive measurement is the data. An analyzing server, which is the heart of use of user log data of individual services when STMS, processes the linked source data and STMS analyzes the traffic volume of individual computes service traffic based on the source services in links. In this article we introduce the data. A web server provides users with a screen detailed functions of STMS and discuss how to on which they can inquire regarding the results compute service traffic. Verification of accuracy of service traffic and statistics. of the results from STMS is also presented by STMS periodically collects network facility comparing them with measured traffic. We share data, user log data of services, and traffic data the experiences we gained during system devel- from related network management systems using opment. Finally, we present a new design FTP. Especially, network facility data provides methodology for IP networks and business sup- connection link information between two pieces port as possible applications of STMS. of equipment (port-level) for reconstituting the

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Traffic data User behavior data Statistics Web server

Service traffic analysis User behavior analysis Failed/subscribers statistics Service traffic VOD user behavior Network facility End-to-end traffic VOD contents usage Subscribers Traffic trend VoIP user behavior Analyzing server Peak time Daily user behavior Overloaded links

Traffic data Service account log Facilities and services contract Access Core Service Channel Network network network VOD log VoIP log contract Collecting traffic traffic log facility information server

NMS IP networks

Figure 2. Configuration and functional entities of STMS.

network topology. The equipment ranges from ment. The connection link consists of upper subscriber aggregation switches to access and equipment and its port corresponding to con- backbone network routers, and application nected equipment, and lower equipment and its servers. User log data for IPTV VOD service, port corresponding to connected equipment. In for example, includes subscriber ID, set-top-box addition, STMS maps subscribers (e.g., IPTV (STB) IP address, event time, VOD contents STB, VoIP phone, and PC) onto an access edge title, VOD server IP address, and bandwidth router because STMS regards the end of the (constant bit rate [CBR]-encoded, bits per sec- subscriber’s part as an access edge router of an ond). Traffic data measured by SNMP in access IP network. Next, according to the transmission and backbone networks provides total port-level policy of each service, STMS computes end-to- traffic information. Table 1 summarizes the end service traffic individually. For doing this, linked source data collected by NMS. STMS configures an end-to-end session of each Based on the source data, STMS analyzes the service from access edge routers to application traffic of individual services, user behavior in the servers using the user log data of services. use of each service, and the statistics of the net- Finally, based on the subscriber’s ID for ser- work facility and subscribers. Regarding traffic vices and the Internet access line linked with data, STMS provides service traffic at the port, access edge routers, the computed service traf- system, and node (e.g., central office [CO]) lev- fic in an end-to-end manner is mapped onto els. Future traffic trends based on time-series links and nodes on the route of the session. analysis as well as traffic ratio of services in links Computing service traffic is explained individu- are provided. User behavior in the use of service ally as follows. includes the average service time and the arrival For IPTV VOD service provided through rate of each service, the ratio of voice and video unicast from VOD servers to a subscriber’s communications, and VOD contents usage rate STB, STMS configures the VOD service session by areas. Statistics of the network facilities and with {access edge router’s IP address, session subscribers are also analyzed and managed at start time, stop time, VOD server’s IP address, the port, system, and node levels. bandwidth} from the collected user log data. Since the original log data only provides a single COMPUTATION OF SERVICE TRAFFIC event time, we need to configure a session from STMS computes the traffic of individual ser- start time to stop time based on the group of vices with collected source data through the fol- the same subscriber’s IP, STB IP, contents title, lowing procedure, illustrated in Fig. 3. After and VOD server IP. The start event includes completely collecting all source data, STMS start, replay, fast forward, and fast backward first reconstitutes the network topology from (rewind), and the end event includes end and access edge routers to backbone networks based pause. When end-to-end traffic computation of on connection link data between network equip- IPTV VOD service has been finished, each ses-

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Data type Management systems Linked source data Interface

{equipment code (upper), port number code (upper), equipment code Facility (backbone) (lower), port number code (lower)} Facility data Facility (access) {subscriber ID, equipment code}

{subscriber ID, STB IP, event time, contents title, VOD server IP, bandwidth}, IPTV (VOD) where event = {start (replay), end, pause, fast forward, fast backward}

{subscriber ID, STB IP, event time, channel number, channel server IP, band- User log data IPTV (channel type) FTP width}, where event = {start, end}

{calling party number, called party number, event time, service type (voice, VoIP video), bandwidth} , where event = {start, end}

{equipment code, port number code, date, incoming traffic (b/s), outgoing Traffic traffic (b/s)} Traffic data IPTV (channel type) {equipment code, port number code, date, total channel traffic (b/s)}

Table 1. Source data collected from management systems.

sion’s traffic is allocated in a timeline to the except for the bidirectional feature of VoIP ser- route of the session composing links and nodes vice, STMS computes VoIP service traffic in all on the network topology. Using the time for links over the entire network. which the session is maintained and the band- Regarding Internet access service traffic, width of the session, STMS computes the aver- STMS gathers the total amount of traffic in all age traffic bandwidth for the session. Let us links. Because the Internet access service does exemplify how to compute the traffic volume of not have any user log data, STMS cannot config- this service in a specific link. It is assumed that ure an end-to-end session for it. Thus, after sub- there are three sessions with 2 Mb/s from 0 to tracting the traffic of all services from the total 30 min (session 1), 6 Mb/s from 10 to 50 min traffic in links, what remains is the Internet traf- (session 2), and 4 Mb/s from 20 to 40 min. As a fic. result, the one-hour average bandwidth of the service in the link is computed as 6.33 Mb/s (= VERIFICATION AND RESULTS OF {2 Mb/s * 30 * 60 s + 6 Mb/s * 40 * 60 s + 4 SERVICE TRAFFIC COMPUTED Mb/s * 20 * 60 s}/3600 s). For IPTV real-time channel service provided The most critical point in the success of STMS through multicast from a head-end center to an development is how accurately the service traffic STB, STMS configures the channel session with computed from user log data reflects the real {access edge router’s IP address, start time, stop traffic. The possible sources of error in STMS time, channel ID, channel server’s IP address, can be classified to one of the following two cat- and bandwidth}. When traffic computation of egories: end-to-end IPTV channel service is finished, • Errors and omissions in source data, such as each channel’s traffic is allocated in the timeline traffic data, user log data, and network to the route of the channel composing links and facility data nodes on the network topology. From Fig. 4, we • Errors in algorithms to compute traffic of can easily understand how STMS computes individual services IPTV channel service traffic in a link. Figure 4a From checking the possible errors, it was shows that seven subscribers watched three dif- found that 1 percent of log data errors are due ferent channels, the traffic of which flowed to missing user log data and mismatch of sub- through the link at different times. Due to the scriber’s contract data, and about 5 percent of multicast nature of IPTV channel service, there network facility data errors are due mostly to are only three channels’ traffic flowing through missing data. Errors in service traffic computing the link, as shown in Fig. 4b. As a result, the algorithms can be verified from the following one-hour average bandwidth of channel service comparison between STMS traffic and measured in the link is computed as 6.33 Mb/s (= {2 Mb/s traffic. Figure 5 compares the IPTV VOD ser- * 50 * 60 s + 4 Mb/s * 50 * 60 s + 2 Mb/s * 30 * vice traffic in a day from STMS with measured 60 s}/3600 s). traffic at VOD server farms located in each A VoIP service session consists of {edge node (CO). Each node shows 24 hours of traffic router for calling party, edge router for called data. In most nodes the computed traffic from party, start time, end time, conversation type STMS is the same as the measured traffic within [voice or video communications], and band- a 5 percent error range. The difference between width}. When end-to-end session traffic is calcu- them is revealed mostly due to errors and loss in lated based on conversation time and bandwidth, network facility data. In addition, to verify the the session traffic is allocated to the route of a algorithm to compute IPTV real-time channel VoIP session on the topology. Very similar to traffic, we tapped traffic at a 1 Gb/s link using a the traffic computation process for IPTV service passive measurement system, and classified the

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An interesting result IPTV STB Head-end center regarding user (VOD server) Facility data behavior in the use VoIP VoIP (called party) (calling party) of VoIP service is IDC/PC that average holding (web server) Internet access time (AHT) between (a) VoIPs is much longer than that between VoIP and PSTN, and User log data between VoIP and mobile phone. AHT (b) from VoIP to mobile phone is reported the shortest time. Traffic data

Figure 3. Service traffic computing process: a) reconstitution of network topology from network facility data; b) end-to-end service traffic computation from user log data; c) allocation of end-to-end service traffic over the entire network.

channel traffic for comparing STMS traffic. The ume than Internet access service. In other words, VoIP traffic computing algorithm was verified by in terms of traffic volume, the cost of IPTV comparing STMS traffic with the measured traf- channel service is five times that of Internet fic of VoIP-level quality of service (QoS) at a access service. This result gives the basis for the differentiated services (DiffServ)-enabled router. settlement of accounts between business depart- From this, we can reason that the service traffic ments and network operating departments with computed by STMS based on user log data will the totally occupied traffic volume of each ser- be the same if the integrity of network facility vice end-to-end throughout the entire network. data and user log data is guaranteed. Traffic volume per user of VoIP service is negli- We add some results of service traffic gible compared to other services. An interesting obtained from STMS. Figure 6 shows the total result regarding user behavior in the use of traffic volume and each service traffic volume VoIP service is that average holding time (AHT) summing up at access edge routers in a day. At between VoIP users is much longer than that the peak time of the network, the Internet access between VoIP and the public switched telephone service occupies about 57 percent of total traffic network (PSTN), and between VoIP and mobile volume, IPTV VOD 9 percent, IPTV channel 34 phones. AHT from VoIP to mobile phone is percent, and VoIP 0.1 percent. The majority of reported to be the shortest. User behavior total traffic volume is still due to the Internet regarding AHT seems mostly due to the differ- access service, but IPTV service traffic has quick- ent chargea for the types of calls. ly soared in the KT network since KT deployed IPTV services in 2007. When it comes close to the backbone network, the effect of IPTV chan- LESSONS LEARNED FROM THE nel traffic gradually decreases due to the feature EVELOPMENT OF of multicasting transmission on which IPTV D STMS channel service relies. VoIP traffic currently In the beginning of the STMS development pro- occupies a very small portion of total traffic vol- ject, the prime obstacle we faced was that we ume, mostly due to the narrow bandwidth of were not sure of the accuracy of service traffic each session, but is fast growing thanks to computed by STMS compared to real traffic increased subscribers. data. To the best of our knowledge, there is no STMS also reports some interesting results attempt to compute service traffic as STMS does regarding the traffic volume per user of services. in academia or industry. As introduced earlier, At the peak time of individual services, the traf- we had to focus on the verification of service fic volume per user of IPTV VOD service is two traffic computed. From our experience during times that of Internet access service. IPTV chan- the verifying process, we found valuable lessons nel service produces five times larger traffic vol- for improving the quality of STMS.

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During verification of traffic computation of IPTV VOD service, we found that there were missing items in user log data that are Subscriber 7 Channel 3 (4 Mb/s) indispensable in computing service traffic. Since KT’s IPTV VOD service is provided by Subscriber 6 Channel 3 (4 Mb/s) streaming, a user can select start, pause, replay, and stop as well as fast forward (FF) Subscriber 5 Channel 2 (2 Mb/s) and fast backward (FB). Initial log data only Subscriber 4 Channel 2 (2 Mb/s) contains the first four events, but the latter Subscriber 3 Channel 1 (2 Mb/s) two events are not provided because these Subscriber 2 Channel 1 (2 Mb/s) events are not indispensable for service provi- Subscriber 1 Channel 1 (2 Mb/s) sioning. Thus, there was missing traffic between the time of FF/FB to stop (or pause). 0 10 20 30 40 50 60 (min) Thus, we asked the IPTV VOD service department to add the two events in the log data, (a) and STMS consequently produces more accurate results. Similarly, there was only the start Channel 3 (4 Mb/s) time of the channel but not its end time in Channel 2 (2 Mb/s) user log data of IPTV channel service. The Channel 1 (2 Mb/s) end time of the channel can be regarded as the start time of a new channel by the same 0 10 20 30 40 50 60 (min) user’s choice at the same time. However, the problem occurs when a user turns off an STB (b) without reporting the end time of the channel. Currently, the IPTV server periodically per- 8 Mb/s forms a health check of the STB, so we may 6.33 Mb/s guess the end time of the channel will be 6 Mb/s halfway between the turning off of the STB 4 Mb/s and the health check. Such an inaccurate log 2 Mb/s data possibly produces errors in producing service traffic. To resolve the problem, we asked 0 10 20 30 40 50 60 (min) to add the end time of a channel in user log data and applied this in STMS. Likewise, the (c) integrity of user log data is the most precious thing for success of STMS. Thanks to the veri- Figure 4. Example of how to compute the average traffic bandwidth of IPTV fying process for STMS functions, we found channel service in a link: a) channel traffic from user log data; b) multicast missing log data and errors in the STB for the channel traffic; c) average traffic bandwidth. log data generating function. There is another issue of integrity for network facility data. Errors and missing data for the network facility are possible in the area STMS process them on an hourly basis. Howev- between access and backbone networks due to er, it is practically very difficult to collect source different ownership of network management. data from NMS every hour while keeping the Since KT owns and manages hundreds of thou- integrity of source data as well as the perfor- sands of switches and routers for IP networks, mance of STMS high. KT has to divide the network into access and backbone with different network management PPLICATIONS OF systems. Thus, we had to check the integrity of A STMS the network facility data located in the shared As it provides traffic-related data, user behavior area managed at different NMS. We then report- data, and facility statistics, STMS has an impor- ed the erroneous data to the NMS for fixing and tant role in a data warehouse for IP network updating them by authorizing the managing task infrastructure in KT. STMS can be expanded to for related equipment. applications such as traffic monitoring, network Finally, we have a comment about manage- facility management, network design, and busi- ment lag time in STMS. Due to the log data ness and management support, including mar- generation by NMS and difficulty of real-time keting promotion and cost accounting for data collecting, STMS collects source data from services. This section introduces two applications NMS daily. In addition, many sessions start just of STMS in IP network design, and in business before 0 o’clock and end after 0 o’clock the fol- and management support. lowing day; thus, STMS can generate the sessions when it collects the log data after another IP NETWORK DESIGN day. It also takes around 7–8 hours for STMS to IP network design in a multiservice environment generate end-to-end session traffic of services should reflect the traffic characteristics and user and compute service traffic in all links over the behavior of services. However, a legacy network entire network based on the source data reach- design relying on total link traffic data is hard to ing around 10 Gbytes. As a result, STMS can apply in a new environment [11, 12]. We thus only report the traffic data around two days after developed a new IP network design methodology the real date. In order to minimize the manage- based on end-to-end traffic data provided by ment lag time, it is recommended to collect the STMS. source data from NMS every hour and have The IP network design process first gathers

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Changes in the traffic route due to factors such 10,000 as routing policy change as well as changes in STMS traffic Measured traffic network topology can easily be reflected in the network design by allocating the end-to-end traf- 8000 fic of each service on the changed routes. Final- ly, we can accurately estimate the cost pricing of services in network building and operation, 6000 because we consider the individual service-related characteristic in the network design. Mb/s 4000 BUSINESS AND MANAGEMENT SUPPORT Since KT merged with Korea Telecom Freetel (KTF), an affiliated company of KT in mobile 2000 wireless communications, in June 2009, KT has been preparing to transition the company struc- 0 ture to a Company-in-Company (CIC) system. A B CD E F Under the CIC system, business departments Nodes and the network operating department have to account for internal trading using network Figure 5. Comparison of STMS traffic and measurement traffic. resources for individual services. Thus, an exact cost accounting between companies becomes a critical issue. The open network environment network facility data, traffic data, user behavior has similar issues in cost accounting between two data, service demands, and routing policy includ- separate companies. Currently, cost accounting ing service transmission route. Next, it config- is mostly performed based on the number of ures the target network topology and computes subscribers, revenue per subscriber, and traffic network design parameters based on the gath- volume at the point of access between two ISPs. ered data. The following process explains how to There is no clear criterion in the cost estimation produce the estimated traffic volume at the tar- of individual services from the viewpoint of net- get year in each link, based on end-to-end traffic work building and operation [13]. Thanks to and network design parameters: STMS, which provides precise information on • For services that provide user log data such the traffic volume for individual services on as IPTV and VoIP, computing end-to-end every link in the entire network, we can now traffic per user of service, based on end-to- estimate the cost of each service based on the end traffic that STMS provides and the traffic volume actually used by users. number of users at an end node (end- Cost pricing of services is just one example of point). what STMS can support. There are wide applica- • Forecasting end-to-end traffic per user of tions of STMS in business and management sup- each service at the target point of time. port. User behavior in the use of services can be • Calculating end-to-end traffic of each ser- utilized as the basic data to establish a business vice by multiplying forecast traffic by future and management strategy, and to support a mar- demands. keting plan for service promotion, new service • Producing offered traffic at links by allocat- development, service pricing policy, and so on. ing the end-to-end traffic to the service Traffic-related information can be utilized to traffic routes, service by service. support decision making by management, as well • Producing designed traffic at links by con- as network operating system improvement. sidering traffic variation over time, because the offered traffic is produced based on the ONCLUSION average peak time of month. To compen- C sate for the traffic difference at the average STMS is a useful tool for building a data ware- peak time of month and day, we compute house for IP network infrastructure in a multi- an adjustment factor and apply it to com- service environment for KT. In addition to pute the designed traffic from the offered service traffic monitoring and management, we traffic. can expect the following merits from STMS in • Performing link and node design that can various areas of applications. First, network accommodate the designed traffic. design can become more accurate and flexible, On the other hand, since the Internet access because it can consider area- and service-specific service does not have end-to-end traffic data, we data, and easily reflect changes in traffic routes need to compute this traffic link by link, not end and network topology. Second, the cost of indi- to end, and add the link traffic to the service vidual services in network building and opera- traffic computed earlier. The capacity planning tion can be more accurately estimated. Third, we design is only related to the downstream traf- knowledge of user behavior in the use of services fic since the traffic volume is much higher than in specific areas is helpful when planning busi- upstream. ness and marketing strategy. In conclusion, dur- The proposed design methodology based on ing this era of open networking and network end-to-end traffic provides the following fea- convergence, KT’s experience in developing tures. As we consider user behavior for individu- STMS is expected to offer a new way for net- al services and the traffic characteristic of each work operation, and a new business strategy for service, it is possible to design networks more global ISPs facing the changed network accurately by reflecting area-specific features. paradigm.

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REFERENCE 2200 [1] K. Knightson, N. Morita, and T. Towle, “NGN Architec- Total traffic ture: Generic Principles, Functional Architecture, and 2000 Internet access Implementation,” IEEE Commun. Mag., vol. 43, no. 10, IPTV channel Oct. 2005, pp. 49–56. 1800 IPTV VOD VoIP [2] C.-S. Lee and D. Knight, “Realization of the Next-Gener- 1600 ation Network,” IEEE Commun. Mag., vol. 43, no. 10, Oct. 2005, pp. 34–41. 1400 [3] C. Fraleigh et al., “Packet-Level Traffic Measurements from the Sprint IP Backbone,” IEEE Network, vol. 17, 1200 no. 6, Nov. 2003, pp. 6–16. Gb/s 1000 [4] J. Quittek et al., “Requirements for IP Flow Information Export (IPFIX),” IETF RFC 3917, Oct. 2004. 800 [5] Procera PacketLogic; http://www.proceranetworks.com/ ______products.html 600 [6] Blue Coat Packetshaper; http://www.bluecoat.com/ 400 ______products/packetshaper [7] P.-C. Lin et al., “Using String Matching for Deep Packet 200 Inspection,” IEEE Computer, vol. 41, 2008, pp. 23–28. [8] S. Jordan, “Some Traffic Management Practices Are 0 Unreasonable,” Proc. 18th ICCCN ‘09, Aug. 2009. 0 123456 7 8 9 1011121314151617181920212223 [9] M. Sidibe and A. Mehaoua, “Service and Network Mon- Hour itoring Support for Integrated End-to-End QoS Man- agement,” Proc. IEEE Net. Ops. Mgmt. Symp. Wksp., Figure 6. Results of service traffic computation. Apr. 2008, pp. 132–37. [10] Cisco Netflow; http://www.cisco.com/ [11] T. Jensen, “Network Planning — Introductory Issues,” R&D Laboratory, KT Corporation since 1994. Her research Telektronik, vol. 3/4, 2003, pp. 9–46. interests are in traffic monitoring/management and net- [12] T. Jensen, “Network Strategy Studies,” Telektronik, work engineering. vol. 3/4, 2003, pp. 68–98. [13] G. Davies, M. Hardt, and F. Kelly, “Come the Revolu- TAEIL CHAE ([email protected]) received his B.S. and M.S. tion — Network Dimensioning, Service Costing and ______degrees from Yonsei University, South Korea, in 1987 and Pricing in a Packet Switched Environment,” Telecom- 1989, respectively, and his Ph.D. degree from Information mun. Policy, vol. 28, 2004, pp. 391–412. and Communications University, South Korea, in 2007. He has been working for Network R&D Laboratory, KT Corpo- BIOGRAPHIES ration since 1993. He has authored a few technical journal papers in areas of optical communications networks, and JUNGYUL CHOI ([email protected])______received his B.S. degree has several patents in optical systems and telecommunica- from Inha University, South Korea, in 2000, and his M.S. tions. His research interests are in next-generation net- and Ph.D. degrees from Information and Communications works, optical packet networks, fixed mobile convergence, University (currently merged with Korea Advanced Institute and network economics. of Science and Technology), South Korea, in 2002 and 2006, respectively. He has been working at the Network BYOUNGKWON SHIM ([email protected])______received his B.S. and R&D Laboratory, KT Corporation (formally, Korea Telecom) M.S. degrees from Hanyang University, South Korea, in since 2006. He has authored around 20 reviewed technical 1985 and 1987. He has been working at the Network R&D journal papers, and holds around 10 patents in telecom- Laboratory, KT Corporation (formally, Korea Telecom) since munications networks. He was nominated for Marquis 1987. As a director and project leader, his research inter- Who’s Who in the World 2009 and International Engineer ests are traffic analysis and engineering for next-generation of the Year for 2010 from IBC. He has been a reviewer of networks, and network economics. technical conference and journal papers for IEEE INFOCOM, IEEE Communications Letters, IEICE Transaction on Commu- JAE-HYOUNG YOO [M] ([email protected])______is a vice president and nications, IEICE Transaction on Information and Systems, group leader in the Network Strategy Research Group, Net- Elsevier Journal of Visual Communication and Image Repre- work R&D Laboratory, KT Corporation. He received his B.S., sentation, and ETRI Journal. His research interests are in M.S., and Ph.D. degrees from the Electronic Engineering next-generation networks, future networks, wired/wireless Department of Yonsei University, South Korea, in 1983, convergence, and network economics. 1985, and 1999, respectively. Since he joined KT in 1986, he has worked on the research and development of various SEUNGHOON KWAK ([email protected])______received his B.S. and networks, QoS management and traffic engineering sys- M.S. degrees from Chonbuk National University, South tems including PSTN, ATM, and fixed and mobile Internet. Korea, in 1995 and 2001, respectively. He has been work- His research interests include routing algorithms, traffic ing at the Network R&D Laboratory, KT Corporation since engineering, fixed and mobile IP network architecture, and 1995. His research interests are in next-generation net- next-generation operation support systems (NGOSS). He works, network dimensioning, and traffic analyzing. was an Application Session Co-Chair of NOMS 2004 and a Special Session co-chair of APNOMS 2006 and 2009. He is MI-JEONG LIM received her B.S. and M.S. degrees from an editorial board member of the International Journal of Chungnam National University, South Korea, in 1991 and Network Management and Journal of Telecommunications 1994, respectively. She has been working at the Network Management.

IEEE Communications Magazine • April 2010 65

TOPICS IN DESIGN &IMPLEMENTATION Safety Assurance and Rescue Communication Systems in High-Stress Environments: A Mining Case Study

Prasant Misra and Salil Kanhere, The University of New South Wales Diethelm Ostry, CSIRO ICT Centre Sanjay Jha, The University of New South Wales

ABSTRACT termed high-stress environments: environments in which by their nature it is intrinsically difficult Effective communication is critical to the suc- to provide communications, and the extreme or cess of response and rescue operations; however, abnormal conditions following an accident or unreliable operation of communication systems disaster, which can both destroy system compo- in high-stress environments is a significant obsta- nents and radically alter environmental condi- cle to achieving this. The contribution of this tions in which the system must operate. We shall article is threefold. First, it outlines those com- focus in this article on one such environment, mon characteristics that impair communication which is both physically harsh under normal in high-stress environments and then evaluates operating conditions, and has significant risk of their importance, specifically in the underground accidents that can damage communications mine environment. Second, it discusses current infrastructure and disrupt communications: underground mine communication techniques underground mines. and identifies their potential problems. Third, it Underground mines are typically extensive explores the design of wireless sensor network labyrinths of long (perhaps several kilometers) based communication and location sensing sys- and narrow (only a few meters in width) tunnels. tems that could potentially address current chal- They may employ hundreds of mining personnel lenges. Finally, preliminary results are presented working at one time under extreme environmen- of an empirical study of communication using a tal conditions and distributed throughout the WSN constructed from commercially available mine. The overall mining process is highly mobile, wireless sensor nodes in an underground mine and mining machinery has to be repositioned as near Parkes, New South Wales, Australia. the mining operation progresses; consequently, the communication environment continually INTRODUCTION changes. The combination of ever-changing ground conditions with a dynamic mining system Communication systems relying on wireless links generates a broad profile of risks, which results in have become integral to industry and to our human casualties in mine accidents [1]. daily life. They now form a core infrastructure Management of the hazards in underground component, which has led to great improve- mines requires continuous monitoring of critical ments in convenience, productivity, and safety. information: the presence and concentration of Their success has led to a desire to make their flammable and toxic gases and dust, the struc- capabilities available reliably in all environments tural integrity and stability of the mine tunnels, of commercial, industrial, and social importance. water ingress, and the current locations and com- Some of these environments inherently present munication status of all underground mine per- challenging technical problems, which constrain sonnel. In the aftermath of an accident, it can be wireless communications. For example, wireless vital to maintain communications with trapped communication between mobile devices inside miners and rescuers, and to establish and track buildings and factories must often operate in their positions. A knowledge of environmental conditions of high signal attenuation, electrical conditions through remote sensors in potential interference, and multiple reflections or echoes, escape routes would aid the preparation, plan- which restrict range and performance. Apart ning, and execution of rescue operations. from those requirements, which arise in specific Regardless of the specific type of high-stress applications, reliable operation requires that a environment, reliable communication is essential communication system should be designed to for successful mine operation under normal con- survive foreseeable accidents and emergencies. ditions, and is vital to the success of emergency These two situations might together be response and rescue operations. Communication

failures in hostile environments can occur inverse power law with an exponent, which because of inadvertent destruction of network depends on material properties of the medium When different infrastructure during normal operations as well (which may vary with operating frequency and paths have large as in emergencies. Failures also occur due to an environmental factors such as temperature and error-prone communication channel in the par- humidity) and the geometry of the channel. The length differences, ticular application environment, and degradation absorption of electromagnetic (EM) waves in their corresponding of the channel after an accident. The term com- water may be so high at usable frequencies that munication channel here notionally lumps togeth- acoustic links can be an alternative to radio or signals interfere to er all the physical components of the system optical links. EM signals are generally strongly cause multipath between the communicating devices, typically attenuated by the Earth at frequencies normally fading and overlap including the material path through which sig- used for wireless communications, but can pene- nals must pass. Conventional communication trate large distances at ultra-low frequencies in time, and may equipment may never be entirely adequate in (hertz to kilohertz). result in distortions some severe high-stress environments, but it is important to identify and investigate the various Extensive Multipath Propagation and Fad- causing a characteristics that prevent satisfactory commu- ing — When a transmitted signal travels by mul- degradation in the nication in such environments, both to map the tiple routes (i.e., multipath) to a receiver (e.g., link quality. range of applicability of different approaches by reflection from surfaces in the environment), and to indicate possible direction that may lead they get added at the receiver antenna. This sum to future advances. typically ranges between a maximum corre- This article provides a summary view of the sponding to the case when all the individual sig- field, which may provide practical benefits to nals add in phase, to a minimum, even zero, other engineers who are working on similar when the signals cancel. The random addition problems and projects. The remainder of the causes space and time fluctuations in signal article is arranged as follows. The next section strength which varies with receiver and transmit- presents a general study of the channel character position, signal frequency, and also move- teristics for high-stress environments, and then ment of the transmitter, receiver, or reflecting examines these characteristics in the specific surfaces (which may be, e.g., vehicles). When case of underground mines. We then outline the different paths have large length differences, various communication techniques used in their corresponding signals interfere to cause underground mines, and provide a brief survey multipath fading and overlap in time, and may of the location sensing and tracking approaches result in distortions causing a degradation in the for these conditions. Wireless sensor networks link quality. (WSNs) have recently been applied to this task, and we provide a concise background and Rapidly Changing Time-Varying Channels — overview of existing work on WSNs, and then Rapid motion of portable communication equip- explore the design of WSN-based communica- ment, as well as variations in the intervening tion systems. This approach is supported by an channel caused by the motion, can cause empirical study of the wireless communication Doppler frequency shifts and rapid signal characteristics of typical commercial WSN nodes strength fluctuations as multipath conditions deployed in an underground mine. The final sec- change. Underwater communication devices may tion suggests potential research directions in the also encounter equivalent acoustic conditions as field of underground mine communication and a result of the motion of the ocean surface and concludes with a summary of the areas covered waves in internal water strata. in the article. Large Propagation Delay and High Delay Variance — This is a prime challenge faced by COMMUNICATION CHANNEL very-long-range communication devices (e.g., HARACTERISTICS satellites and deep space communication), as C well as underwater communications where the This section first outlines the general channel acoustic propagation is some 200,000 times slow- properties that are common to what we have er than EM waves in air. Variations in the effec- called high-stress or harsh environments, and tive path length of the signals due to then specializes them to the unique channel con- non-homogeneous material along the path can ditions prevalent in underground mines. cause changes to the total propagation time and also introduce a large variance in path delays. HIGH-STRESS ENVIRONMENTS Communication channels in high-stress environ- Noise — Noise in the communication system, ments share several characteristics that make whether externally or internally generated, reliable operation difficult [1–4]. reduces the effective system sensitivity and therefore maximum range. Some environments Extreme Path Loss Due to Signal Absorp- (e.g., the vicinity of high-power electrical motors) tion and Geometric Spreading — The trans- can have high noise levels, which can degrade mitted signal is attenuated by absorption in the radio communication. Noise levels can be severe medium through which the signal travels, and by in satellite and deep space communications the geometric effect of the wavefront area because of EM radiation from transient solar expanding as it propagates away from the trans- storms and background astronomical sources. In mitter. Both these effects cause a decrease in the ocean storm, wave motion, shipping, and signal strength with range from the transmitter. even biological activity can generate severe The dependence on range typically has an acoustic noise.

IEEE Communications Magazine • April 2010 67

attenuation. Restrictions on LOS communication arise from the normal mine arrangement of long orthogonal tunnels, support pillars, tunnel blockages, and floor undulations.

Ionized Air — Fires generate ionized air, which Miner 1 Leaky feeder cable can act as a plasma and disturb EM propagation transmitting Signals are leaking along the in mines. entire length of the cable. Humid and Warm Conditions — The relative humidity in mines is high, typically greater than 90 percent and the ambient temperature is commonly around 28°C.

Gaseous Hazards — The main component of Miner 2 the flammable gases that leak from coal seams is receiving methane. When the concentration of methane exceeds a critical threshold, an explosive mixture is formed with a risk of gas blasts. Hence, contin- ual ventilation is required to decrease the build- up of dangerous gases. However, in the case of a disaster, power supply to the mine equipment may be cut, possibly leading to failure of the ventilation system with the risk of dangerous gas accumulation. Equipment for use in coal mines Figure 1. Wireless communication mediated through fixed leaky feeder cables. in most jurisdictions must be certified as explosion-proof (i.e., unable to trigger an explosion in air containing any proportion of methane). Besides these factors, stringent power con- Besides these natural environmental condi- straints, topological variability, lack of interoper- tions, every mine is unique with its own distinct ability, and the use of fixed communication operating considerations. In addition to the infrastructure [1] are important characteristics of above environmental properties, there are other harsh environments. As a consequence of all channel characteristics specific to underground these factors, communication systems may suffer mines. from limited bandwidth, intermittent link connectivity, high distortion and link error and Waveguide Effect — Mine tunnels can act as packet loss rates, unacceptable packet reception waveguides at certain frequencies, and allow rel- jitter, and delay (important in the case of low- atively low-loss propagation, which can provide latency applications such as voice and video). long-range communication. This behavior is discussed in more detail in the next section. UNDERGROUND MINES Underground mines are generally structurally Noise — The EM channel is effectively shared non-uniform, with a network of interconnected with all the other electrical systems in the mine, tunnels, crosscuts, shafts, escape ways, first-aid leading to background noise. Electric machinery, stations, alcoves, and tunnel blockages. Some of power cabling and other mining appliances can the tunnels may contain rail tracks and conveyor generate noise in some of the frequency bands belts. The walls are generally rough and the used by underground communication devices, ground surface uneven, and scattered regions of and hence can have an adverse effect on their accumulated water may be present. Some parts performance. Other independent systems using of the wall and ceilings may be strengthened wireless links can also contribute to the back- with bolted wooden grids and metal beams. ground noise. In a disaster response and recovery Environmental conditions that affect communi- situation, noise levels may be temporarily cation in mines include the following [1, 5]. reduced due to power shutdowns, but heavy mechanical rescue equipment and other electron- Dynamic Changes in Underground Topolo- ic equipment may introduce additional noise. gy — The location of mine walls and faces may alter continuously as a result of mining operations. UNDERGROUND INE OMMUNICATION Instability in Mine Structures — Some extrac- M C tion techniques use collapse zones where there This section describes some of the communica- are no supports and the faces are allowed to col- tion techniques that have been applied in under- lapse as mining operations proceed, or in the ground mines, and outlines recent approaches to event of seismic activity. communication and tracking devices.

Limited Line of Sight— Having a line of sight COMMUNICATION TECHNIQUES (LOS) between transmitter and receiver can sig- Communication techniques applied in mines can nificantly improve communication, as signals can be classified as one of three basic types [5]: propagate directly rather than through material Through-the-Wire (TTW), Through-the-Air or around corners, both of which cause excess (TTA), and Through-the-Earth (TTE).

68 IEEE Communications Magazine • April 2010

Name Type Advantages Disadvantages

Telephones TTW Easy operation Vulnerable to damage from roof falls, mine fires, and explosions

Pager phones TTW + TTA Cheap; simple operation One-way

Trolley Fixed/mobile — can provide communi- Limited coverage; constant vibration; warm, humid, and dusty TTW phones cation to all rail haulage vehicles conditions; interference from electrical machinery

Hoist Limited to communication between the hoist cage and sur- TTW Simple operation phones face/underground stations

Wireless communication; portable; two- Walkie- TTA way; can connect to nearby communi- Generally poor range but may have good LOS performance talkie cation infrastructure (e.g., leaky feeder) Table 1. Communication devices.

Through-the-Wire — As in systems deployed design, the main difficulties in an underground above ground, a fixed infrastructure can pro- wireless system arise from the properties of the vide routine long-distance communication in communication channel and noise sources. harsh mine environments. Signals can be sent In general, EM propagation between two over electrical conductors such as twisted pair arbitrary points in a mine level requires propaga- and coaxial cables, and via optical fibers [1, 2]. tion through the Earth, down tunnels, around Cabling primarily intended for other purposes, corners and past machinery blockages. All these such as to provide power to electric rail vehi- conditions cause strong attenuation and signal cles (trolleys), can also be used to carry signals. degradation, dependent on both operating fre- A major disadvantage of these systems is that quency [1] and the specific environment. underground personnel must use equipment The material through which mine tunnels are that is physically connected to the cables for constructed typically behaves as a low-loss dielec- signaling, whereas communication with unhin- tric, allowing a tunnel to act as a waveguide, dered mobility is a prime requirement under- with relatively low-loss EM propagation possible ground. Hybrid systems, such as those using along it [5]. Ideal waveguides have a characteris- leaky feeders, which use fixed wiring to dis- tic frequency called the cutoff frequency, below tribute signals accessed by wireless connections which EM waves cannot propagate. The cutoff to nearby miners (Fig. 1) will be discussed in the frequency is directly related to the tunnel cross- next section. section dimensions, and for typical mines the Although the performance of TTW systems cutoff frequency is in the tens to low hundreds is satisfactory for routine operations, fixed of megahertz (i.e., the very high frequency cabling is prone to damage and breakage in [VHF] band). Above the cutoff frequency, EM accidents involving fire, earth falls, and tunnel waves can propagate by essentially following disruptions, and is difficult to maintain [5]. In paths that bounce along the tunnel walls at a order to improve the reliability of TTW sys- grazing angle. At each reflection, some signal tems, various cable protection schemes have energy is lost by scattering from irregularities in been applied, including deployment through the tunnel walls and floor, and refraction into conduit, burying the cable, feeding cables the surrounding material. The loss tends to be through borehole connections to main lines, greater at higher frequencies. LOS waveguide and redundant cabling [1]. However, these propagation can be surprisingly good at ultra methods are expensive, make maintenance high frequency (UHF) [6], with the best perfor- more difficult, and increase system complexity. mance in coal mines typically at around 900 Fiber optic cables have a significant advantage MHz in the UHF band and providing ranges of over conventional wired communication tech- some hundreds of meters. Below the cutoff fre- niques as they are not susceptible to electrical quency, waveguide propagation is not possible, interference and generally have far lower atten- although direct LOS propagation can allow com- uation with distance. Some existing communica- munication over a short range. tion devices [2, 5] that use TTW techniques are Long-range across-mine communications can shown in Table 1. be implemented with hybrid systems in which signals are carried sequentially in both fixed Through-the-Air — TTA systems use wireless TTW infrastructure and generally shorter wire- links to allow untethered mobile communica- less links. The TTW infrastructure can have tions. The environmental conditions in both met- translation or bridge equipment at regular spac- alliferous and coal mines present a unique set of ing to convert signals from cable form to wire- challenges for wireless communications. A sim- less UHF signals, for example, which can be ple model of a wireless communication system used by miners with portable and handheld comprises a transmitter, which generates and UHF equipment. This approach combines some launches an EM signal, the communication of the benefits of both TTW and TTA systems, channel through which the signal propagates, but also carries the disadvantage that the fixed and a receiver. Apart from the practical con- infrastructure is vulnerable in mining accidents. straints on portable transmitter and receiver Two common hybrid forms use either UHF or

IEEE Communications Magazine • April 2010 69

Extremely low Very low Low Medium Very high Ultra high frequency frequency frequency frequency frequency frequency (ELF) (VLF) (LF) (MF) (VHF) (UHF) (30–300 Hz) (3–30 kHz) (30–300 kHz) (300–3000 kHz) (30–300 MHz) (300–3000 MHz)

Decreases Bandwidth Increases

Antenna Increasessize Decreases

Decreases Attenuation Increases

IncreasesNoise level Decreases

Figure 2. Influence of operating frequency.

medium frequency (MF) signals at around 1 All the above systems can be combined to MHz. A UHF implementation typically uses extend the range over which communication is leaky feeder cables mounted along selected tun- possible and to provide system redundancy by nels as the fixed infrastructure. Leaky feeder providing independent modes of operation. cable is specially constructed to allow a proportion of EM signals traveling in the cable to both Through-the-Earth — The attenuation of EM escape into the environment and enter the cable signals through the ground strongly depends on from the environment. Two separated miners, operating frequency. Figure 2 shows the qualita- each near the leaky feeder, can communicate via tive dependence of several factors: available sig- this cable using UHF handsets. The signal trans- nal bandwidth, attenuation, antenna size, and mitted by one is picked up by the leaky feeder noise levels on the frequency. These trade-offs cable, propagates down the cable while being prevent a system operating in one frequency partly re-radiated into the environment along band from satisfying all operational and emer- the whole cable length, and the second miner gency requirements. can receive this signal. EM signals at the operating frequencies typi- MF signals strongly couple to continuous cally used by TTA systems are unable to pene- metal conductors and can use them as the long- trate rock strata. However, attenuation of EM range transmission medium rather than specially signals through the earth (TTE) decreases with constructed leaky feeders. Miners use MF equip- frequency, and at very low frequencies, ranges ment, generally bulkier and less portable than can become great enough to allow even direct UHF equipment, to generate signals that are surface-to-underground communication [5]. TTE carried along purpose-deployed single metallic communication systems typically operate between conductors, or suitable pre-existing structures 90 Hz and 4 kHz, and typically must use large such as lifelines or power rails. One benefit of loop antennae to launch EM signals efficiently at MF systems is that, in case of an accident, it may these frequencies. The data rates required for be possible to use any available undamaged con- speech cannot be supported at these frequencies, ductors to traverse blocked tunnel regions. so communications are limited to text messages. A natural extension of the hybrid approach Efficient antennas must be large (perhaps even uses a deployment of wireless nodes to form a kilometers in diameter to support direct surface- wireless mesh network, which can forward mes- to-miner operation), and miners may have to sages from a miner within range of any node to a deploy wire loops underground as required. The destination point in the network where the mes- capability of direct communication with trapped sage can be either delivered or forwarded through miners, independent of below-ground mine infra- other communications systems. The availability of structure, makes provision of TTE systems par- multiple paths in these networks gives them resis- ticularly important in mine emergencies. tance to link failures, which are likely to occur in TTW, TTA, and TTE communication tech- emergencies. Digital modulation technologies nologies have their distinct capabilities and limi- (e.g., as used in WiFi networks) have been devel- tations, which makes selection of a suitable oped to operate at high data rates in the severe system or combination of systems strongly multipath environments typical of mines, and dependent on the particular application [2]. hence may be able to support speech and video communications. Because of their flexibility and TRACKING SYSTEMS potential performance in a range of difficult envi- The majority of current tracking systems are based ronments, wireless mesh networks are the subject on radio frequency identification device (RFID) of active current research. technology. RFIDs or tags are small electronic

70 IEEE Communications Magazine • April 2010

devices that can communicate with more complex reader nodes via wireless communications. Reader nodes can interrogate tags to exchange identity and other information. Two main systems are currently being used. In the first, miners carry RFID tags, and reader nodes placed at known fixed positions are connected to a mine communications system, which can send data back to a central collection point. When a miner passes within range of a reader, the tag identity is transmitted back to the control center, giving an indication that a particular miner is located within the reception zone of the reader. Position resolution depends on the density of reader nodes in the mine and their coverage areas. In the alternate system known as reverse RFID, the RFID devices are deployed at known positions. The miners now carry portable readers, which interrogate the static RFID devices for their identity and transmit the information back to a central site via the miners’ existing communication system. As mentioned previously, underground wireless communications can be implemented via a mesh network of fixed nodes (Fig. 3). This raises the possibility of integrating communication and positioning functions in one system. At its sim- The system reconfigures when a node in a route fails plest, the identities of the nodes nearest to the and determines a new route for communication. miner can give zone position information. Sys- tem performance can be improved by combining Figure 3. Node-based tracking system: a wireless mesh network. link information, such as signal strength and propagation timing measurements, to allow more precise localization. for integration with deployed systems and Information about research agencies, manu- planned enhancements facturers, and commercially available tracking • Modifications required to make WSN nodes systems can be found in [1, 7]. usable in the mining environment and able to provide the desired data SIN NDERGROUND INES • Long sensor node life through use of both WSN U M batteries high in energy density or recharge- The general dependence on TTW systems for able using available energy sources, and operational use, together with restricted environ- techniques to minimize node power con- mental monitoring capabilities, is a limitation in sumption while carrying out network opera- providing safety assurance and rescue communi- tions cation capabilities. This section investigates the • Physical protection of the WSN nodes and feasibility of applying the emerging WSN tech- sensors to prevent damage or faulty opera- nology to implement a location sensing and envi- tion in normal and post-accident circum- ronmental monitoring system, and discusses stances without adversely affecting related work and our own experiences in the communications deployment of a WSN in an underground mine • Network protocols to store, exchange, and in Parkes, New South Wales, Australia. retrieve information reliably under harsh operating conditions BACKGROUND • System health monitoring to establish and WSNs provide a new option for portable wire- report the functional status of the system less communication systems, by using a network during normal conditions as well as after of WSN nodes to provide the required network the occurrence of a mine accident connectivity in a cheap and efficient manner. • System maintainability, that is, the effort WSN devices are also well suited to distributed required to keep the system operational in environment monitoring, and can report gas and both normal and emergency conditions dust concentrations and geological stability data • Decision systems to present sensor data in a over their deployment range by attaching suit- way that can be easily interpreted to assist able sensors. operational and emergency planning

REQUIREMENTS FOR A AN EMPIRICAL STUDY IN AN WSN IN HARSH ENVIRONMENTS UNDERGROUND MINE There are a number of important factors that In order to assess the limitations of currently must be considered in order to design a WSN available commercial WSN nodes when deployed implementation for location sensing and envi- as a wireless communication network in under- ronmental monitoring in underground mines: ground mines, we conducted a series of experi- • Availability of sensors and nodes suitable ments using off-the-shelf MicaZ [1] wireless

IEEE Communications Magazine • April 2010 71

received by the base station from a majority of the motes. Hence, a second experiment was con- 0 Base ducted with the motes placed much closer to station each other, as shown in Fig. 4. 10 Figure 5 shows the percentage of packets received correctly at the base station from each 8.5 m of the individual motes. The success rate is less 9 than 50 percent for most of the motes. The results suggest that those motes at one hop dis- 1 tance from the base station (motes 1 and 10) 14 m and with a clear LOS (mote 10) performed better than the other motes. Several factors were 12 m identified that could have contributed to the low 2 packet reception rate: dynamic channel changes 8 due to personnel motion during the tests; slight 8.8 m misalignment of antennas due to the mounting 12 m method, and multiple reflections from the mine 3 walls and other metallic objects attached to them. In addition, we believe that variations in 7 11 m the performance of the individual mote radios also influenced packet throughput, as some motes achieved good signal strength and perfor- 9.5 m 4 mance, while others failed to communicate at the same distance in a similar configuration. Our 4 m experience highlights the need for custom design 6 5 of wireless sensor nodes that can provide reli- 5 m able communication in harsh environments.

EXISTING WORK We provide here a brief survey focusing on work Figure 4. Experimental setup inside the mine. directed to the systems design and deployment of WSNs in underground mines. Li et al. [8] present a sensor network deployment and collabo- sensor nodes (motes) in an underground gold rative communication strategy to detect the and copper mine located near Parkes, New structural changes in the event of underground South Wales, Australia. mine collapses. Field studies were conducted through the deployment of a prototype system Deployment — The mine tunnel that was acces- consisting of 27 Crossbow Mica2 motes in the D. sible for experimentation was approximately 5 m L. coal mine in China. The prospects of using in width and 10 m in height, and had projecting ultra-wide-band (UWB) signals in conjunction bolts positioned approximately 2 m above the with WSNs for localization in underground tunnel floor. MicaZ motes were enclosed in mines have been studied by Chehri et al. [9]. plastic boxes to act as a protective casing, with Measurement data for simulation were collected the antennas protruding. The plastic boxes con- from the CANMET experimental mine in Cana- taining the MicaZ motes could be mounted on da. Xuhui et al. [10] describe the implementation the bolts in the tunnel walls. Mote 0 was config- of a methane gas sensor and propose an auto- ured as the base station, while all the other matic calibration technique with the help of net- motes (numbered 1–10) were sited along both work connectivity. FireFly, a new sensor walls of the tunnel, as depicted in Fig. 4. An hardware platform based on a cross-layer solu- experiment was conducted to test whether motes tion for tracking and voice communication in 1–10 were able to successfully send packets to harsh environments, was introduced in Mang- the base station across multiple hops. All the haram et al. [11]. The experimental results motes were programmed using TinyOS and nesC reported in that work were collected in a NIOSH [1]. The packet length was fixed at 29 bytes with experimental coal mine. Xiaodong et al. [12] a simple structure comprising a header and a describe their experiences in monitoring the coal payload containing the mote identification code. mine conditions via a wireless network consisting Packets were sent at intervals of 100 ms, and of Crossbow MicaZ sensor nodes equipped with approximately 6000 packets were sent from each custom developed multifunctional sensor boards. mote over a period of 10 min.

Discussion — It proved to be more difficult RESEARCH DIRECTIONS AND than expected to set up the experiment in the ONCLUSION humid and dusty mine environment. Coordinat- C ing the deployment of sensor motes inside a The performance of communication and track- dark underground mine tunnel and conducting ing systems in underground mines has not been experiments is a nontrivial task in practice, as as actively or extensively researched as contem- the acoustic properties of the tunnel do not per- porary surface-based systems. There are few mit people to speak to each other if they are existing systems, and there is limited public more than 50 m apart. When the motes were information regarding implementation details placed at 15 m intervals, no packets were and actual performance in mines. Ensuring safe-

72 IEEE Communications Magazine • April 2010

ty of mining personnel is one of the dominant issues driving the development of these systems. 80 However, the difficult conditions in mines and 70 the lack of practical approaches have prevented the development of a robust and generally appli- 60 cable safety system. In view of experiences 50 learned from mining accidents, there is a need to 40 research the applicability of new technologies in mine environments. Current systems lack the 30 capability of sensing and assessing information Success rate (%) 20 that could help in predicting the risk of an acci- 10 dent. There is a need to engineer early warning systems to bridge this gap because there is only a 0 very limited capability to limit the intensity and 1 2 3 4 5 6 7 8 9 10 impact of a disaster when it strikes. Node ID Currently available tracking systems only reg- Figure 5. Success rate vs. node ID. ister that a person is within a certain region or zone. Research is needed into autonomous and robust tracking systems capable of high spatial [10] Z. Xuhui and W. Sunan, “Design of a Wireless Sensor Network for Methane Monitoring System,” 6th IEEE resolution in real-time continuous tracking. Int’l. Conf. Industrial Informatics, 2008, pp. 614–18. Wireless systems using spread-spectrum or UWB [11] R. Mangharam, A. Rowe, and R. Rajkumar, “Firefly: A radios that promise accurate positioning togeth- Cross-Layer Platform for Real-Time Embedded Wireless er with robust communication in strong-multi- Networks,” Real-Time Sys., vol. 37, no. 3, 2007, pp. 183–231. path environments, and software defined radios [12] X. Wang et al., “Deploying a Wireless Sensor Network able to adapt to dynamic propagation conditions on the Coal Mines,” IEEE Int’l. Conf. Net., Sensing, are other promising research areas that could Control, 2007, pp. 324–28. address some of the challenges posed by radio propagation in mines. BIOGRAPHIES This article outlines features common to a PRASANT MISRA ([email protected])______is a Ph.D. stu- range of high-stress environments and described dent in the Networks Research Laboratory (NRL), School of the factors that may affect communication in Computer Science and Engineering, University of New deployments in these environments. It identifies South Wales (UNSW), Sydney, Australia. His research interests have been in the area of wireless sensor networks, those factors that present the greatest challenges network embedded systems, and wireless networks. He is a to reliable communication in underground recipient of the Australian Leadership Awards (ALA) schol- mines. Properties of the underground wireless arship, awarded by the Australian Agency for International channel, and the design and implementation of Development (AusAID), Government of Australia. He received his B.E. (Hons) in computer science and engineer- current approaches to communication and tracking from Sambalpur University, India, in 2006, and worked ing using this channel are also discussed. Finally, as a senior software engineer in Keane Inc., Bangalore, the article discusses the emerging technology of India, 2006–2008. WSN deployments in harsh environments and its SALIL KANHERE received his M.S. and Ph.D., both in electrical applicability in underground mines, and we engineering, from Drexel University, Philadelphia, Pennsyl- describe our preliminary experiments to assess vania, in 2001 and 2003, respectively. He is currently a the operation of WSNs in mines using general- senior lecturer in the School of Computer Science and purpose commercial nodes. Engineering, UNSW. His current research interests include participatory sensing, vehicular communication, and wireless mesh and sensor networks. REFERENCES DIETHELM OSTRY [M] ([email protected])______is a research scien- [1] P. Misra et al., “Safety Assurance and Rescue Communi- tist in the Wireless and Networking Technologies Laborato- cation Systems in High-stress Environments,” tech. rep. ry, ICT Centre, CSIRO Australia. His recent research interests UNSW-CSE-TR-0912, Univ. New South Wales, 2009. have been in the areas of wireless networks, data network [2] Niosh Office of Mine Safety and Health Research, “Tuto- traffic characterization, optical packet networks, and wire- rial on Wireless Communications and Electronic Track- less sensor networks. He holds a B.Sc.(Hons) in physics ing,” working draft, May 2009; http://www.msha.gov/ from the Australian National University and an M.Comp.Sc. ______techsupp/PEDLocating/WirelessCommandTrack2009.pdf from the University of Newcastle, Australia. [3] I. F. Akyildiz, D. Pompili, and T. Melodia, “ Underwater Acoustic Sensor Networks: Research Challenges,” Ad SANJAY JHA is a professor and head of the Network Group Hoc Net. J., 2005, pp. 257–79. at the School of Computer Science and Engineering at [4] I. F. Akyildiz et al., “Interplanetary Internet: State of the UNSW. He holds a Ph.D. degree from the University of Art and Research Challenges,” Comp. Net., vol. 43, no. Technology, Sydney, Australia. His research activities cover 2, 2003, pp. 75–112. a wide range of topics in networking including wireless [5] L.K. Bandyopadhyay, S. K. Chaulya, and P. K. Mishra, sensor networks, ad hoc/community wireless networks, Wireless Communication in Underground Mines, resilience/quality of service (QoS) in IP networks, and Springer, 2010. active/programmable networks. He has published over 100 [6] A.G. Emslie, R.L. Lagace, and P.F. Strong, “Theory of the articles in high-quality journals and conferences. He is the Propagation of UHF Radio Waves in Coal Mine Tun- principal author of the book Engineering Internet QoS and nels,” IEEE Trans. Antennas Propagation, vol. AP-23, a co-editor of the book Wireless Sensor Networks: A Sys- no. 2, Mar. 1975. tems Perspective. He is an Associate Editor of IEEE Transac- [7] P. Misra, D. Ostry, and S. Jha, “Underground Mine tions on Mobile Computing. He was a Member-at-Large, Communication and Tracking Systems: A Survey,” tech. Technical Committee on Computer Communications rep. UNSW-CSE-TR-0910, Univ. New South Wales, 2009. (TCCC), IEEE Computer Society for a number of years. He [8] M. Li and Y. Liu, “ Underground Coal Mine Monitoring has served on program committees of several conferences. with Wireless Sensor Networks,” ACM Trans. Sensor He was the Technical Program Chair of the IEEE Local Com- Net., vol. 5, no. 2, 2009, pp. 1–29. puter Networks 2004 and ATNAC ‘04 conferences, and Co- [9] A. Chehri, P. Fortier, and P. M. Tardif, “UWB-Based Sen- Chair and General Chair of the Emnets-1 and Emnets-II sor Networks for Localization in Mining Environments,” workshops, respectively. He was also the General Chair of Ad Hoc Net., vol. 7, no. 5, 2009, pp. 987–1000. the ACM SenSys 2007 Symposium.

IEEE Communications Magazine • April 2010 73

SERIES EDITORIAL

TOPICS IN INTEGRATED CIRCUITS FOR COMMUNICATIONS

Charles Chien Zhiwei Xu Stephen Molloy

n the past ten years, we have witnessed rapid advances trical energy from the environment (e.g., body motion, I in communication technology that enabled more than ambient light, and thermal gradient). Existing short-range an order magnitude increase in throughput and reduction radios such as ZigBee, adopted for building automation in power consumption. The steep rise in available through- and home energy management, still dissipate too much put has stimulated the growth of ubiquitous broadband power to self-sustain based on energy harvesting. services such as streaming of high-definition video con- In this issue of the Topics in Circuits for Communica- tents, while on the other extreme, the steep drop in power tions Series, we have selected three articles that mark consumption, in particular for short-range radio technolo- recent progress in the communications semiconductor gies, has enabled personal area connectivity for all kinds of industry for highly integrated radio system-on-chip (SoC) portable consumer electronic devices, such as headsets, that enables future trends in broadband delivery of cell phones, and cameras. Current third-generation (3G) enhanced high-definition video contents and self-powered mobile devices easily support data rates on the order of health monitoring systems. 1–10 Mb/s, while quasi-static devices can easily support up In the first article, “Video Encoder Design for High to 600 Mb/s with wireless LAN based on IEEE 802.11n. Definition 3D Video Communication Systems,” the For short distances, Bluetooth and ZigBee connectivity authors address the challenges to realizing efficient technology consume power as low as 10–50 mW. encoders for emerging bandwidth constrained consumer In the next few years, we will continue to see expansion video applications, which have recently expanded beyond of available throughput to meet the increasing demand to current HDTV to the higher-resolution quad-HDTV as access high-definition (HD) contents such as Blu-ray quali- well as three-dimensional video. Two key challenges in ty video over the Internet. Such increase in demand has reaching these incredible processing rates are memory propelled infrastructure upgrades for higher-speed back- bandwidth and the complexity of context-adaptive binary bone technology such as Data over Cable Service Interface arithmetic coding (CABAC). The article describes new Specification (DOCSIS) 3.0, which achieves four to eight architecture and circuit techniques to address these two times higher throughput compared to its predecessor, ver- key challenges. Novel caching is applied to minimize exter- sion 2.0. Typical deployment of DOCSIS 3.0 achieves nal memory bandwidth, while algorithm parallelism at the throughput of 171–343 Mb/s by means of channel bonding. frame level is applied to the CABAC bottleneck. The The improved throughput makes it possible to download authors then demonstrate an example implementation and high-definition contents from the Internet with low laten- test chip for the architecture, capable of encoding a single cy. A further push in broadband capabilities will be driven view at a resolution of 4096 × 2160 or multiple views at by enhanced visual renderings such as 3DTV, which cap- lower resolution. tures stereo information in two optical polarizations, one The second article, “An Embedded 65nm CMOS Base- for each eye. At a minimum, the additional stereo infor- band IQ 48MHz-1GHz Dual Tuner for DOCSIS 3.0,” mation doubles the throughput requirement. While 3DTV exemplifies a fully integrated embedded complementary volume has reached only 1.2 million in 2009, its volume is metal oxide semiconductor (CMOS) digital dual tuner for projected to hit 46 million by 2013. DOCSIS 3.0 and set-top box applications. To compete Another future trend points to ultra-low-energy radio with higher throughput offered by gigabit passive optical systems for remote monitoring of vital signs in patients or network (GPON) and very high bit rate digital subscriber people with pre-existing health conditions. Such systems line (VDSL), cable providers introduced DOCSIS 3.0, require implants that make regular replacement of batter- which offers an increase in throughput by bonding multiple ies inconvenient. Ideally, suitable technologies should be downstream channels. Coexistence with high-powered ana- capable of replenishing wasted energy by harvesting elec- log cable transmissions imposes substantial challenges on

74 IEEE Communications Magazine • April 2010

SERIES EDITORIAL

the integrated tuner design that has to demodulate eight technologies that are enabling new and emerging commu- downstream channels simultaneously. To maintain low nication systems. If the reader is interested in submitting a power dissipation, the authors describe a cost-effective paper to this series, please send your paper title and an multichannel and multituner solution by integrating the abstract to any of the Series Editors for consideration. tuner, digital demodulator, MPEG decoder, memory, and processor core on a single SoC. The article covers several critical design issues, such as harmonic rejection for BIOGRAPHIES demodulation, image rejection with imbalance canceller, CHARLES CHIEN is president and CTO of CreoNex Systems, which focuses on technology development for next-generation systems. Previously he held and high dynamic range front-end. The authors also pro- various key roles at Conexant Systems, SST Communications, and Rock- vide detailed design trade-offs in the tuner architecture well. In his career he has architected several key products including a and RF circuit design issues, as well as the benefit of their CMOS/SiGe chipset for multimedia over coax (MoCA), an IEEE 802.11abg WLAN RF CMOS transceiver and GaAs PA/RF switches, a wireless audio unique implementation with respect to power consumption CMOS chipset for home theatre in a box, CDMA2000 cellular RF CMOS and cost in future technology scaling. transceivers, and low-power wireless networked sensors. He was also an The third article, “Integrated Electronic System Design assistant adjunct professor at the University of California at Los Angeles (UCLA) from 1998 to 2009. His interests focus mainly on the design of for Implantable Wireless Batteryless Blood Pressure Sens- system-on-chip solutions for wireless multimedia and networking applica- ing Microsystem,” reviews the recent techniques used in tions. He has published in various journals and conferences, and has authored a book entitled Digital Radio Systems on a Chip. He received his real-time monitoring of blood pressure to identify genetic B.S.E.E. from the University of Caifornia at Berkeley, and his M.S. and susceptibility to diseases. These techniques provide critical Ph.D. from UCLA. He was a member of the technical program committee research tools to develop new treatments for cardiovascu- of ISSCC from 1998 to 2006.

lar and hypertension. In contrast to conventional monitor- ZHIWEI XU received B.S. and M.S. degrees from Fudan University, Shanghai, ing techniques that rely on invasive bulky catheter tip China, and a Ph.D. from UCLA, all in electrical engineering. He held indus- transducers, an implantable miniature lightweight blood try positions with G-Plus Inc., SST communications, Conexant Systems, and NXP Inc., where he did development for wireless LAN and SoC solutions for pressure sensing microsystem with wireless data communi- proprietary wireless multimedia systems, CMOS cellular transceivers, MoCA cation and adaptive RF powering capability is highly desir- systems, and TV tuners. He is currently with SST as department head, working on various aspects of wireless communication SoC and software able. However, the integration of a batteryless wireless defined radios. His current research interests include wireless communica- communication system with real-time blood pressure moni- tion SoCs for high data throughput as well as ultra-low-power applications. toring remains a challenge. The authors describe design He has published in various journals and conferences, made one contribution to the Encyclopedia of Wireless and Mobile Communications, and has challenges with respect to various circuits and microsystem four granted and five pending patents. impairments such as continuously changing RF power coupling and magnetic field. The article then describes design STEPHEN MOLLOY received M.S. and Ph.D. degrees in electrical engineering from UCLA in 1993 and 1997, respectively, where his research focused on techniques to boost the circuit immunity to dynamic envi- low-power circuits and architectures for video signal processing. This work ronment and interferences, and demonstrate the integrated led to the award of the Showman Prize from UCLA in 1997, and resulted in over a dozen conference and journal publications. He received a B.S. blood pressure sensing microsystem for future implantable degree in electrical engineering from Rensselaer Polytechnic Institute in integrated health monitoring systems. 1991. He served as Associate Editor of the IEEE Journal of Solid-State Cir- We would like to take this opportunity to thank all the cuits from 2001 to 2004 and was a member of the technical program committee of the IEEE International Solid-State Circuits Conference from 1998 authors and reviewers for their contributions to this series. until 2005. He is currently vice president of engineering at Qualcomm, Future issues of this series will continue to cover circuit leading architecture development.

IEEE Communications Magazine • April 2010 75

INTEGRATED CIRCUITS FOR COMMUNICATIONS Video Encoder Design for High-Definition 3D Video Communication Systems

Pei-Kuei Tsung, Li-Fu Ding, Wei-Yin Chen, Tzu-Der Chuang, Yu-Han Chen, Pai-Heng Hsiao, Shao-Yi Chien, and Liang-Gee Chen, National Taiwan University

ABSTRACT In a real-time HD 3D video communication system, three key technologies make it feasible. VLSI realization of video compression is the The first one is the stereo or multiview capturing key to real-time high-definition 3D communica- and display device. The second one is the coding tion systems. The newly established multiview standard. Since 3D video contains many different video coding standard, as an extension profile of view angles, different and more efficient coding H.264/AVC, draws more and more attention for algorithms than the conventional single-view its high compression ratio and free-viewpoint video coding standards are required to further support. Besides providing the 3D experience, reduce the bit rate for communication. Third, the multiview video can also give users complete efficient hardware architecture is required for scene perception. However, the multiple-view- accelerating the coding speed to meet the real- point throughput requirement of MVC increase time constraint. Because of the multiple-view- the complexity and hardware cost dramatically. angle characteristic, data needed to be processed The system memory bandwidth, on-chip memory in a 3D video is multiple times that in a conven- size, and processing data throughput of each tional single-view video. Thus, if the conventional module all need to be optimized in an MVC architecture is adopted, it will multiply computa- encoder. Therefore, efficient hardware solutions tion complexity and hardware cost. for MVC architecture design are needed. In this In order to transmit and store 3D/multiview article an overview of 3D video coding standards contents, an efficient multiview video coding developments and design challenges of an MVC (MVC) scheme is needed. The MPEG 3D encoder are discussed. Then the algorithm and Audio/Video (3DAV) Group is working on the architecture optimization schemes are proposed. standardization of MVC. In July 2008, MVC was For the trade-off between system memory band- standardized as the Multiview High Profile in width and on-chip memory size, a cache-based H.264/AVC by the MPEG 3DAV Group [2]. prediction engine is proposed to ease both The joint MVC (JMVC) was released by the design challenges. Moreover, the hybrid open- MPEG 3DAV Group as the reference software close loop intra prediction scheme and the and research platform [3]. In the JMVC frame-parallel pipeline-doubled dual CABAC H.264/AVC is adopted as the base layer. In solve the throughput requirement problem. At addition, disparity estimation (DE) and disparity the end of this article, based on all the proposed compensation (DC), the most significant fea- solutions, a prototype single-chip MVC encoder tures in JMVC, can effectively discover the design with processing ability of 4096 × 2160 sin- interview redundancy of a multiview video and gle-view to 1280 × 720 seven-view is presented. save 20–30 percent of bit rates. Based on the bit rate reduction, an HD MVC sequence is able to INTRODUCTION be stored in high-end multimedia portable storage like a Blu-ray disc. However, the coding For advanced TV applications, vivid perception complexity increases dramatically in the MVC quality is required. Therefore, higher and higher because of the hybrid inter-view DE and intra- video resolutions, like high-definition (HD) 720p view motion estimation (ME) prediction (1280 × 720 pixels) and 1080p (1920 × 1080 pix- schemes. Furthermore, the processing through- els), are recommended. In addition, 3D video put requirement of HD MVC is many times can bring the 3D and realistic perceptual experi- larger than that of the current HDTV specifica- ence to viewers by projecting different views to tion. Thus, a new and efficient encoder architec- users’ left and right eyes simultaneously. As the ture design for the MVC is desired. In this article technology evolves, lots of 3D related applica- the mainstream 3D video coding standards, tions, such as 3D-TV and free-viewpoint TV, are design challenges in MVC encoder design, and emerging [1]. the proposed solutions are briefly introduced.

The video coding standard development is intro- In order to solve the problems of the previ- duced in the next section. The hardware resource ous standards, MVC is proposed as an extension MVC outperforms analysis is then presented. Then the proposed profile of H.264/AVC. In contrast to the single- previous 3D video MVC architecture design is shown. The final view-plus-depth format, MVC encodes video section concludes this article. data from multiple viewing angles into a single coding standards bitstream by hybrid motion and disparity com- by use of pensated prediction. Figure 1 illustrates the FROM 2D TO 3D: VIDEO CODING overview of an MVC system and the correspond- H.264/AVC-based STANDARD DEVELOPMENT ing block diagram of an MVC encoder. The coding scheme. The multiview video is captured by a camera array, multiple view angles 2D VIDEO CODING: FROM MPEG-1, followed by the MVC encoder compressing the H.261 TO H.264/AVC multiview video data for transmission or storage. characteristic also On the decoder side, reconstructed multiview avoids the quality Video data without compression is impossible to video can be displayed on various displays such transmit directly due to the incredible size of the as currently commercialized HDTV, or nearly uncertainty due to uncompressed raw data. Since 1990 many video developed stereo and multiview 3DTV. In an the depth map. coding standards have been defined for storage MVC encoder, video frames from the first view However, these and transmission. Among these coding stan- channel are compressed by a typical H.264/AVC dards, coding efficiency is the most important encoder. On the other hand, DE and DC are features also bring criterion. There are two main series of video adopted to other view channels to further reduce the larger complexity coding standards: the International Standards inter-view redundancy. This multiple-viewpoint Organization (ISO) MPEG-x standards and characteristic of MVC avoids the quality degra- and hardware cost International Telecommunication Union — dation from the inaccurate depth map. Further- than previous Telecommunication Standardization Sector more, the H.264/AVC-based encoding flow standards. (ITU-T) H.26x standards. The MPEG-x series reduces the bit rate overhead for each view. contains MPEG-1, MPEG-2, and MPEG-4. On However, the complexity of an MVC encoder is the other side, the H.26x series starts from H.261 also much higher than that of the single H.264/ in 1990 to H.263, H.263+, and H.26L. Further- AVC encoder due to its multichannel character- more, some standards are the result of cowork- istic. Therefore, an efficient hardware architec- ing of these two groups. For example, MPEG-2 ture is urgently required. is also called H.262 and is the result of a common project. Then H.264 is delivered by both ISO and ITU-T, which is also called the Joint DESIGN CHALLENGES OF AN Video Team (JVT). Therefore, H.264 can also NCODER be called MPEG-4 Advanced Video Coding HD MVC E (AVC) or H.264/AVC. Being the latest finalized MVC outperforms previous 3D video coding advanced video coding standard from these two standards by use of an H.264/AVC-based coding main streams, H.264/AVC has the best coding scheme. The multiple view angles characteristic performance. It provides more than 50 percent also avoids the quality uncertainty due to the bit rate reduction over the previous MPEG-2 depth map. However, these features also bring standard. In order to provide better and better larger complexity and hardware cost than previ- rate distortion (R-D) performance in the future, ous standards, especially when the resolution at the last MPEG meeting, a new Joint Collabo- requirement is as high as the HDTV specifica- rative Team between MPEG and ITU was creat- tions. The main design challenges of an MVC ed to work on a new standard. encoder are shown in Fig. 2 and discussed below.

3D VIDEO CODING: ULTRA HIGH COMPUTATION COMPLEXITY AND FROM MPEG-2 MULTIVIEW PROFILE TO MVC THROUGHPUT REQUIREMENT 3D video has always played an important role in MVC has large computational requirements the video processing research field, including, of because it needs to compress data from multiple course, 3D video coding. The first finalized 3D viewpoints. In a video coding system, inter-frame video coding standard was the MPEG-2 Multi- redundancy elimination causes most of the com- view Profile. A stereo video sequence can be plexity. For a single-view video, ME is used to compressed into a bitstream containing a base find out the inter-frame relationship and reduce layer and an enhancement layer. In addition to the data redundancy in the temporal domain. In the stereo-view representation, another approach MVC DE is used as well for the inter-view to 3D video is the single-view-plus-depth, or so- domain inter-frame prediction. For an N-view called 2D + Z, format. The Advanced Three- multiview sequence, this hybrid ME/DE encoding Dimensional Television System Technologies scheme requires more than N times more com- (ATTEST) from European Information Society putation than a single-view sequence. Figure 2a Technologies (IST) and MPEG-C Part 3 from shows the integer ME/DE (IMDE) computation MPEG both focus on this format. The depth analysis under different resolutions and view information can be captured by the depth sen- numbers, where different search algorithms used sor. With the depth map, virtual views can be in integer ME/DE and the corresponding compu- generated by depth image-based rendering tation requirements are listed. Two hardware ori- (DIBR). However, the technology of depth map ented algorithms are considered in Fig. 2a. The generation is not mature enough. It directly full search algorithm uses all possible candidates causes quality degradation of the rendered virtu- over the entire search window (SW) and thus al views on the receiver side. provides the best rate-distortion (R-D) perfor-

IEEE Communications Magazine • April 2010 77

In the architecture Output design field, the Input various representation multiview video system memory bandwidth and the HDTV on-chip memory size are two major Stereo TV limitations. The trade-off between them is classic in MVC Storage/ MVC encoder transmission decoder architecture design. That is, larger Multiview on-chip memory 3DTV allows lower system memory bandwidth.

Input frame Entropy From view 1 Block engine coding Compressed data

Intra prediction

Motion Motion compensation Frame(s) estimation memory MV Vector coding M First view channel u l Second view channel MV and DV Vector t coding i Bitstream p Frame(s) l Motion/disparity memory e Motion/ compensation x disparity e r estimation Intra prediction

Input frame Entropy From view 2 Block engine coding

Third view channel

Nth view channel

Figure 1. Overview of an MVC system and the block diagram of an MVC encoder.

mance. However, it requires huge computation. Another design challenge of an HD MVC Hierarchical search is a fast algorithm to reduce encoder is the large data throughput require- the computation. By hierarchically downsampling ment. To encode an N-view MVC sequence, the SW, the required number of search candi- the throughput requirement is about N ore dates can be reduced to about 10 times less than more times that of encoding a conventional that of full search. However, the computation is single-view sequence. However, throughput on still too large to be processed for the HD MVC some modules cannot be enlarged by simply specifications. As shown in Fig. 2a, the required duplicating and parallel processing. Taking the instructions per second (IPS) is over 1000 GIPS entropy coding, for example, the entropy coder even when hierarchical search is adopted. Mean- in H.264/AVC and MVC, content-based adap- while, the high-end quad-core CPU by Intel, tive binary arithmetic coding (CABAC), has QX9770, can only provide 60 GIPS. According to very strong data dependence since it needs to this analysis, hardware acceleration is needed for consider the previous symbols when generating an HD MVC encoder design. the current symbol. Therefore, most existing

78 IEEE Communications Magazine • April 2010

CABAC symbol rate 2000 IMDE computation in MVC Maximum symbol count 1E+5 1800 Average symbol count 1600 1E+4 1400

1E+3 1200 60 GIPS== 1000 QX9770 Symbols/MB 1E+2 800

Instructons/s (GIPS) 600 10 Throughput limit of one-symbol CABAC Full search 400 Hierarchical search 1 200 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Frame number 1280 x 7201280 x 2 x 7201280 x 3 x 7201920 x 4x 1080 1920x 2 x 1080 x 3 (a) (b)

SRAM size in MVC System bandwidth in MVC 10000 10 Level C Level C+ Level D 1000 Hier.

100 1 kbytes

Gbyte/s Level C 10 Level C+ Level D Hier. 1 0.1

1280 x 720 x 2 1280 x 7201280 x 3 x 720 1920x 4 x 1080 x 19202 x 1080 x 3 1280 x 720 x 2 1280 x 720 1280x 3 x1920 720 x 41080 x 21920 x 1080 x 3 (c) (d)

Figure 2. Design challenges in an HD MVC encoder: (a) IMDE computation analysis; (b) CABAC throughput analysis; (c) system bandwidth analysis; (d) on-hip SRAM size analysis

CABAC coder designs can only provide the because of the data dependence issues men- throughput of one symbol per clock cycle. tioned above. Therefore, a new and efficient However, this processing ability is far from the architecture is required. target HD MVC throughput. Figure 2b illustrates the frame-by-frame symbol count analy- HIGH SYSTEM MEMORY BANDWIDTH AND sis result on an HDTV sequence. The red line LARGE ON-CHIP MEMORY SIZE is the largest throughput of a one-symbol CABAC coder. This throughput limit is calcu- Since hardware acceleration is needed according lated from the operating frequency and video to the analysis above, further system and memo- resolution. Take our target HD MVC specifi- ry analysis is required before the implementa- cations, for example. Considering the system- tion. In the architecture design the system on-chip (SoC) integration compatibility, the memory bandwidth and on-chip memory size are highest operating frequency of the previous two major limitations. The trade-off between H.264/AVC encoders is selected as no more them is classic in architecture design. That is, than 200 MHz [4–6]. However, when the target larger on-chip memory allows lower system specifications are as high as the HD MVC, the memory bandwidth. available processing cycles for a macroblock In a video encoder design, IME, or IMDE in (MB) is only about 350 cycles even the operat- MVC, requires most of the bandwidth and on- ing frequency is increased to 300 MHz. As chip memory because a large SW must be load- shown in Fig. 2b, the symbol count has large ed onto the chip for doing IMDE. Typically the variance between frames because the symbol width and height of the SW are set to about 10 counts of the I-frame and P-frame are much percent of the frame width and height, respec- higher than that of the B-frame. A convention- tively. Furthermore, more than one SW is load- al CABAC coder can barely deal with the aver- ed when the frame type is B-frame or the age case, but is infeasible for the maximum multiple-reference-frame scheme is enabled. In symbol rate. Unfortunately, the symbol rate order to reduce the hardware cost, various data cannot be raised by increasing the parallelism reuse schemes, including level C, level C+, level

IEEE Communications Magazine • April 2010 79

350 Cycles/stage

Stage 2: IMDE Stage 1: IMDE Pf Stage 6: Stage 7: Stage 8: Stage 3: NOP IP and Stage 5: MDC REC Dual-EC and DB FMDE Stage 4: FMDE Pf

MVC encoder chip View-parallel MB-interleaved CTRL

View1 cache SRAM EC select EC IP core 1 core IMDE IMDE Residue Bitstream buf. core prefetch MB SRAM Cur. MB EC buf. Cur. Luma core 2 MB buf. IMDE core FMDE Bitstream buf. core MDC core Cur. MB buf. FMDE IMDE core prefetch Cur. Luma Rec. MB MB buf. MDC MB SRAM SRAM DB MB SRAM View2 cache SRAM

128-bit system bus interface

System external DRAM controller Bus mater/slave Processor Video input memory External bus

IMDE: Integer ME/DE IP: Intra prediction REC: Reconstruction EC: Entropy coding FMDE: Fractional ME/DE MDC: Motion/disparity compensation Pf: Prefetch DB: Deblocking

Figure 3. Proposed eight-stage MB pipelined MVC encoder architecture. Note that each stage has about 350 processing cycles if the processing frequency is 300 MHz under HD MVC specifications.

D, and hierarchical search, have been proposed configurations. From Fig. 2d, when the target in recent years [7]. The system memory analysis specification matures, the maximum memory of these algorithms for MVC with different requirement may be as high as dozens or even numbers of views and resolutions are shown in hundreds of millions of gates, which is far Figs. 2c and 2d. Different trade-offs between beyond what a high-end SoC system can support. bandwidth and memory size are selected under Therefore, a smart strategy to reduce both on- different algorithms. For example, level D data chip memory size and system memory bandwidth reuse has the largest on-chip SRAM size and is desired. lowest memory bandwidth. From the bandwidth point of view, a high-end SoC with a fairly wide 128-bit bus can only support about 4 Gbytes/s PROPOSED MVC bandwidth even under 100 percent bus utiliza- ENCODER SOLUTIONS tion and 250 MHz operating frequency. Mean- while, the required bandwidth is over 5 Gbytes/s SYSTEM ARCHITECTURE for nearly all algorithms listed in Fig. 2c for 1a Figure 3 shows the system architecture of the 080p three-view MVC sequence. On the other proposed MVC encoder. The encoder contains hand, if the TSMC 90LP process is used, the seven kinds of computation cores, including inte- lowest point in Fig 2d, which is about 60 kbytes, ger ME/DE (IMDE), fractional ME/DE occupies the equivalent gate count from 0.57 to (FMDE), intra prediction (IP), motion and dis- 1.94 million under different memory compiler parity compensation (MDC), reconstruction

80 IEEE Communications Magazine • April 2010

(REC), entropy coding (EC), and deblocking fil- or the quality drops greatly. To prevent this ter (DB). from raising SW cost, the proposed algorithm A motion According to the design challenges described shown in Fig. 4b takes the relationship between above, instead of simply raising the parallelism MVs into consideration. Since MBs inside the information preserv- from the conventional three-or four-stage MB same object should have similar MVs, MVs from ing scheme is pipelined architecture in the previous the neighboring MBs can be set as the initial proposed to main- H.264/AVC encoder design [4–6], an eight-stage search hint of the current ME process. If we put MB pipelining is proposed. In order to ease the the SW around the best hint instead of the zero tain the quality on hardware cost of IMDE, the inter-frame predic- MV, the required SW size can be dramatically the complex motion tion part is split into five MB pipeline stages, reduced because of the inter-MB MV similarity. and the cache-based prediction core is adopted. Based on this concept, the detailed algorithm field by getting more After the cache memory is used, two SW flow of the proposed predictor-centered algo- accurate initial hints prefetching stages for IMDE and FMDE are rithm is described as follows. First, several initial and refining centers. added to load SWs into on-chip SRAM prior to hints are set, and each has a tiny SW. The win- the processing stage. They not only reduce the dow size is 4 × 4 in our implementation. Second, In the proposed burden of the pipeline-cycle budget but also each candidate in these windows is sent to the scheme, motion enhance the hardware utilization of IMDE and IMDE module, and a corresponding R-D cost is FMDE cores. An no operation (NOP) stage is calculated. The candidate with the best R-D cost information is saved inserted to deal with the data dependence is chosen as the refinement center, and a larger and reused in the between the prefetching and processing stages. refinement range is defined around it. However, intra-coded MBs. After the inter-frame prediction is done, the this multiple hints and refinement flow may intra-frame prediction and motion/disparity com- cause a larger quality drop in cases with non-uni- pensation are performed in parallel in the sixth form motion fields. A motion information pre- stage. The reconstruction stage reconstructs the serving scheme is proposed to maintain the compressed frame as the reference for the fol- quality on the complex motion field by getting lowing frames. Finally, two CABAC EC modules more accurate initial hints and refining centers. and one DB module are processed simultane- In the proposed scheme motion information is ously in the eighth MB pipeline stage. According saved and reused in the intra-coded MBs. The to the analysis in the previous section, each MV predictor defined in the standard pipeline stage only has about 350 cycles under H.264/AVC is derived from the MV field. As a the target HD MVC specifications. result, when an MB is intra-coded, its motion information is not encoded, and no MV is avail- PREDICTOR-CENTERED CACHE-BASED able. However, if the MV pointing to the best MOTION/DISPARITY ESTIMATION matched block is stored, even if the intra mode wins the inter/intra mode decision, the MV can According to the analysis in the previous section, still be used as a hint for neighbor MBs. There- the IMDE part accounts for most of the hard- fore, motion information is reused instead of ware cost. One major reason is that it requires a being discarded even if the block is intra-coded. large SW buffer, which grows proportionally to After the proposed scheme, the R-D perfor- the frame resolution. Based on previous work on mance on all the test sequences used in JVT fast search, only 30 percent of the SW area is H.264/AVC meetings can be maintained as less really used in common intermediate format than 0.1 dB drop even when the SW size is as (CIF), and this utilization decreases to 15 per- small as ±16 × ±16 under our target HD MVC cent in D1 video. That is, much data is loaded to specifications. the on-chip SW buffer unnecessarily. However, Based on this multiple hints with refinement if we directly shrink the search range, the R-D scheme, the SW can be retargeted MB by MB performance drops greatly. These two character- dynamically, and therefore the requirement on istics indicate that we only need a small part of SW size is reduced. Figures 4c and 4d illustrates data in the SW, but we cannot assume that the how the predictors are generated. The perfor- location of this part is always close to zero-MV. mance of this predictor-centered algorithm highly Therefore, a predictor-centered cache-based depends on the accuracy of hints. If the hint tar- IMDE is proposed. The SW is centered by the gets a wrong region, it needs a larger refinement predictor, so the search range can be reduced range to compensate for the quality loss, and the with little quality degradation. The cache memo- benefit of the predictor-centered algorithm is ry trades off the possibility of cache misses for a decreased. Two kinds of hints are used to exploit much smaller on-chip memory capacity, and is the spatial and temporal correlation of MVs inside still able to handle the varying and dynamic data the same object. The first is the intra-frame pre- access pattern. dictors, which are MVs/DVs from the neighbor- Figures 4a and 4b are the comparison hood MBs. Since the video processing is done in between the conventional ME algorithm and the raster-scan order, only MBs above or left to the proposed predictor-centered algorithm. Figure current MB have MVs available. Thus, the 4a shows the concept of previous hardware-ori- MVs/DVs from the top, top-left, top-right, and ented algorithms. In order to find the relation- left MB are used as the intra-frame predictors. ship between frames, a SW is set on the Furthermore, the zero MV and motion vector pre- reference frame around the relative location of dictor (MVP) defined in H.264/AVC and MVC, the current MB. That is, the center of the SW is which is the median-filtered result of the top, top- the zero motion vector (MV). Since the length right, and left MVs, are also allocated as intra- of MV grows proportionally to the dimension of frame predictors. The inter-frame predictors are video frames, the size of SW also needs to be the other kind of predictors. Because an MVC enlarged to keep the best-matching MV inside, sequence consists of more than one viewpoint, one

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Because of the splitting of the intra Frame Search Current Initial search window macroblock hint prediction and reconstruction stages, only one best matched mode is Ref. Current Ref. Current required for frame frame frame frame reconstruction. Consequently, the ME ME cycle budget is enough even under the close-loop Time Time scheme. t – 1 t t – 1 t (a) (b)

View 1 View 2 View

Current frame MVs from neighboring DV MBs 1 t – 1 MV 2 MV1

t DV2 Cur. MB Currrent frame

Time MV1 + DV1 ~=MV2 + DV2

MV2 from best matching MB . (c) (d)

Figure 4. Proposed IMDE algorithm: a) concept of previous hardware oriented algorithms; b) the proposed predictor-centered algorithm; c) intra-frame predictor generation and reuse; d) inter-view predictor generation and reuse.

object may be captured in more than one view at The cache system provides flexible data access. the same time. Since the object is the same, the However, the cache miss penalty is considerable. captured motion in different cameras are also sim- Every time the wanted data are not in the cache, ilar. Therefore, the MVs from the neighboring the system needs to be stalled, and the required views are very strong predictors [8]. In fact, after data is reloaded from the external memory. This including the inter-frame predictors, the required stall-and-reload waiting time lowers the hardware refinement range can be shrunk to 4 × 4, the same utilization. Therefore, two new MB pipelines, size as the tiny search window for a hint. That is, IMDE prefetch and FMDE prefetch, are added the refinement step in ME can be canceled for to the proposed MVC system architecture to those views under both ME and DE [9]. lower the cache miss rate. After this scheduling In order to support the dynamic hint refinement optimization and other proposed cache architec- access pattern without loading all the pixels in all ture optimizations, including priority-based possible locations of SW, a cache system is imple- replacement policy and a concurrent SW mented as the SW buffer. Unlike the conventional prefetching and reading scheme, the total cycles cache memory system in the computer architecture of cache miss penalty are reduced by 93 percent. field, cache memory used in video processing has That is, only 1.2 misses will happen during one several different features. The most significant dif- MB pipeline stage, which has 350 cycles. ference between them is that video data has 2D spatial coherence rather than the 1D addressing in HYBRID OPEN-CLOSED LOOP INTRA PREDICTION general cache memory design. To fully utilize this Other than the inter-frame prediction, intra- coherence, the internal index wraps in two dimen- frame prediction is also used for reducing the sions. The three-tuple vector (x, y, frame-index) is spatial redundancy within a frame. Pixels are translated to the tag address and the tag. A tag set is predicted from the neighboring pixels. In the pointed by the tag address, and the tag is compared H.264/AVC high profile and MVC, there are to that set. Upon a cache hit, the word address three kinds of intra predictions: intra4 × 4 (I4) locates the word in a five-banked on-chip SRAM. mode, intra8 × 8 (I8) mode, and intra16 × 16

82 IEEE Communications Magazine • April 2010

1080p HDTV D1 SDTV Task

Setup Intra_4x4 14 Intra_4x4 14 Intra_4x4 14 Blk0 Blk0 Blk0 Blk1 ... Blk15 Blk15 Intra_8x8 ... Pred. Rec Pred. rec Pred. R ec

I16 I16 I16 Blk1 Chroma ... Chroma Blk0 Blk0 5 Mode0 Mode4 Cycles 910 1300 (a)

Use reconstructed pixels Task HD MVC Intra_16 Intra_16 Intra_16 Blk Blk Blk0/1 Blk2/3 ... Blk14/15 Blk Blk Pred. Pred. Pred. 0 1 2 3 Setup Intra_4x4 Intra_4x4 Intra_4x4 Prediction Blk0/1 Blk2/3 ... Blk14/15 Blk Blk Use original stage Blk Blk pixels Pred. Pred. Pred. 4 5 6 7 Intra_8x8 Intra_8x8 Blk0 ... Blk4 Blk Blk Blk Blk Pred. Pred. 8 9 10 11 Reconstruction Reconstruction of stage the best pred. mode Blk Blk Blk Blk from I16/I4/I8 Cycles 12 13 14 15 272 320 350

(b) (c)

Figure 5. Issues and solutions on the intra stage: a) illustration of the throughput bottleneck due to data dependence; b) the pro-posed hybrid open-close loop intra prediction; c) the corresponding processing scheduling.

(I16) mode. The 4 × 4 discrete cosine transform fication is based on the assumption that the dif- (DCT) is used in I4 and I16, while the 8 × 8 ference between the original and reconstructed DCT is used in I8 mode to further improve the pixels is very small if the target peak signal-to- coding efficiency. In previous H.264/AVC noise ratio (PSNR) is higher than 35 dB. In our designs, intra prediction for the baseline and target HD multiview environment, this assump- main profile are well developed for lower speci- tion works well. For MB boundaries, the recon- fications like D1 (720 × 480 pixels) and HD structed pixels are still used as predictors since 720p. However, there are two main design chal- these pixels are already reconstructed in the pre- lenges that lower the efficiency of previous vious MB pipeline stages. The proposed process- designs. The first issue comes from the data ing schedule is shown in Fig. 5c. Intra prediction dependence between each subblock. According on Blk0 and Blk1 in Fig. 5c can start simultane- to the definition of I4 and I8 modes in ously because Blk1 does not need the recon- H.264/AVC standard, each subblock should be structed pixels from Blk0. Therefore, the processed in zig-zag scan order. Since the pre- parallelism of intra prediction can be largely dictor pixels in the intra prediction are generat- improved to meet the target HD MVC specifica- ed from neighboring blocks and are not available tions with little quality loss. However, this open- until the neighboring blocks are reconstructed, loop scheme cannot be adopted to the each subblock should be processed sequentially. reconstruction step because the original pixels This data dependence also causes the other are not available in the decoder side, and mis- design challenge of low hardware utilization. As match between the encoder and decoder would Fig. 5a shows, sequential processing scheduling break standard compliance. For this reason, the makes it difficult to increase the parallelism. reconstruction step is split as a standalone stage. Thus, it costs about 1300 cycles to finish intra MBs are reconstructed in a closed-loop manner prediction of one MB in a D1-size video under in the reconstruction stage. Because of the split- single-view encoding. However, as mentioned ting of the intra prediction and reconstruction before, the cycle count available for one MB is stages, only one best matched mode is required only around 350 cycles under the target HD for reconstruction. Consequently, the cycle bud- multiview specifications. get is enough even under the closed-loop scheme. In order to improve the throughput, the hybrid open-close loop intra prediction scheme is FRAME-PARALLEL PIPELINE-DOUBLED proposed to break the data dependence described DUAL CABAC above [10]. It is illustrated in Fig. 5b. For subblock boundaries, the original pixels instead of Entropy coding compresses data based on the the reconstructed pixels are used as the intra pre- probability distribution of symbols, and it plays dictor, and this is the open-loop part. This modi- an important role in video coding. In the base-

IEEE Communications Magazine • April 2010 83

Data1 Data2 ctx2 ctx1 Ctx state State (2-symbol) CABAC Read state 2*(206:1 table)

Syntax Symbol Range Range Update Binarization element Binary Index arithmetic Bitstream Context coding Low Low

Context Ctx Update Side Bypass information modeling

comparators Write state Output Output 2*(3:1 table) (a) Ctx state Output1 Output2 (b)

Task

CABAC CABAC CABAC view1 view1 view1 . . . MB1 MB2 MB3 CABAC CABAC CABAC view2 view2 view2 . . . MB1 MB2 MB3

350 Cycles Cycle budget of other MB pipelines

(c)

(d)

Figure 6. Issues and solutions on the CABAC stage: a) the system overview of CABAC; b) proposed two-symbol arithmetic coder; c) the frame-parallel scheme of the CABAC stage further improves the symbol rate; d) chip photo of the proposed MVC encoder.

line profile, H.264/AVC adopts context-based arithmetic coder. Finally, the arithmetic coder adaptive variable length coding (CAVLC) as the generates an output bitstream. entropy coder. In the main profile or other Due to the limited cycle budget in the MB advanced profiles, including the MVC, CABAC pipeline architecture, an EC engine with a one- is adopted. CABAC achieves 9 to 14 percent bit symbol arithmetic encoder can only process rate savings over CAVLC, but its computation is about 350 symbols in one MB pipeline stage. As much more complicated. Furthermore, due to discussed earlier, this throughput ability is way the sequential nature of arithmetic coding, the below the target HD MVC spec. Therefore, the hardware design makes it extremely difficult to multisymbol CABAC architecture is proposed exploit pipelining or parallel techniques. [11]. The arithmetic coder is duplicated as in Figure 6a shows the block diagram of Fig. 6b. For range stage, low stage, and output CABAC. The inputs of CABAC are syntax ele- stage, two one-symbol PEs are directly cascaded. ments (SEs) and side information. Syntax ele- However, we cannot simply cascade two one- ments are the essential data to be coded, such as symbol state stages because they are possibly the MB type, prediction mode, and residues. Side same. The two-symbol state stage is shown on information, usually the information of neigh- the right of Fig. 6b. The proposed two-symbol boring coded blocks, helps to estimate the prob- arithmetic coder may not provide exactly dou- ability of symbols. These SEs must be bled throughput since the throughput depends transformed into binary symbols before binary on the ctx types. Based on our simulation, the arithmetic encoding. The adaptive effect is actual throughput of the proposed two-symbol achieved through the context (ctx) assigned to coder is 1.94 times larger than the conventional the symbol. These ctxs are modeled according to one-symbol/clock cycle architecture. the SE type, side information, and binary index. Applying the two-symbol CABAC architec- Symbols with the same ctx have similar statistical ture can double the throughput. However, for properties and use the same adaptive probability some textured MBs, the two-symbol CABAC state for estimation. Besides normal arithmetic architecture still does not meet the throughput coding, bypass mode is introduced to speed up requirement. Based on the analysis from previ- the encoding process. The symbol along with its ous work, the critical path increases with the associated ctx and bypass flag enters the binary number of concurrently processed symbols in the

84 IEEE Communications Magazine • April 2010

arithmetic coder. For our target operating fre- the single view QFHD H.264/AVC encoding is quency, 250–300 MHz, architectures processing also supported. With the proposed VLSI tech- The frame-parallel more than two symbols in parallel are not feasi- niques, real-time 3D video applications become ble. Therefore, frame-parallel pipeline-doubled feasible, and we believe more and more 3D scheduling scheme dual (FPPDD) CABAC is proposed to utilize video consumer products can be realized in the can be adopted to frame-level parallelism. Dual CABAC computa- near future. avoid data tion cores are adopted, and each CABAC core has a doubled pipeline cycle budget of 700 cycles. REFERENCES dependency These CABAC computation cores process in an [1] ISO/IEC MPEG Video and Requirements Group, “Appli- between the two interleaved manner as shown in Fig. 6c. Thus, cations and Requirements on 3D Video Coding,” the frame-parallel scheduling scheme can be ISO/IEC JTC1/SC29/WG11 N10857, 2009. cores. With the [2] Joint Video Team of ISO/IEC MPEG and ITU-T VCEG, circuit-level and adopted to avoid data dependence between the “Joint Draft 7.0 on Multiview Video Coding,” ISO/IEC two cores. With circuit- and frame-level opti- JTC1/SC29/WG11 and ITU-T SG16 Q.6 JVT-AA209, Apr. frame-level mization, the throughput of the proposed 2008. FPPDD CABAC is 3.88 times that of the one- [3] Joint Video Team of ISO/IEC MPEG and ITU-T VCEG, optimization, the “WD 1 Reference Software for MVC,” ISO/IEC symbol design. JTC1/SC29/WG11 and ITU-T SG16 Q.6 JVT-AA212, Apr. throughput of the 2008. proposed FPPDD CHIP IMPLEMENTATION [4] Y.-W. Huang et al., “A 1.3TOPS H.264/AVC Single-chip Besides the above algorithm and architecture Encoder for HDTV Applications,” IEEE ISSCC Dig. Tech. CABAC is 3.88 times optimization, all the other modules, including Papers, 2005. [5] Y. K. Lin et al., “A 242mw 10mm2 1080p H.264/AVC of the one-symbol the view parallel MB interleaved (VPMBI) High-profile Encoder Chip,” IEEE ISSCC Dig. Tech. scheduling controller, fractional motion/disparity Papers, 2008. design. estimation [12], and motion/disparity compensa- [6] Z. Liu et al., “A Real-Time 1.41w H.264/AVC Encoder SOC for HDTV 1080p,” IEEE Int’l. Symp. VLSI Circuits tion, are also optimized. After adopting all the Dig. Tech. Papers, 2007. proposed solutions, a prototype MVC single [7] C.-Y. Chen et al., “Level C+ Data Reuse Scheme for chip encoder was fabricated by Taiwan Semicon- Motion Estimation with Corresponding Coding Orders,” ductor Manufacturing Company (TSMC) with IEEE Trans. Circuits Sys. Video Tech., vol. 16, no. 4, Apr. 2006, pp. 553–58. 90 nm 1P9M process [13]. The chip photo is [8] L.-F. Ding et al., “Content-aware Prediction Algorithm shown in Fig. 6d. The core size of the chip is with Inter-View Mode Decision for Multiview Video 11.46 mm2 (3.95 mm × 2.90 mm), which contains Coding,” IEEE Trans. Multimedia, vol. 10, no. 8, Dec. 1732 kgates. This chip supports both H.264/AVC 2008, pp. 1553–64. [9] P.-K. Tsung et al., “Cache-Based Integer Motion/Dispari- Multivew High Profile and High Profile at level ty Estimation for Quad-HD H.264/AVC and HD Multi- 5.1. For multiview video coding, the proposed view Video Coding,” Proc. IEEE Int’l. Conf. Acoustics, MVC chip can support from the full HD 1080p Speech, Signal Process., 2009, pp. 2013–16. three views to the HDTV 720p seven views. [10] T.-D. Chuang et al., “Algorithm and Architecture According to this view scalability, the processing Design for Intra Prediction in H.264/AVC High Profile,” × Proc. Picture Coding Symp., 2007. ability can be as high as 4096 2160p if the view [11] Y.-J. Chen, C.-H. Tsai, and L.-G. Chen, “Architecture number is only one. Thus, the proposed chip can Design of Area Efficient SRAM-Based Multi-Symbol support not only the HD MVC encoder, but also Arithmetic Encoder in H.264/AVC,” Proc. IEEE Symp. Circuits Sys., 2006, pp. 2621–24. the quad full HD (QFHD) H.264/AVC single- [12] P.-K. Tsung et al., “Single-Iteration Full-Search Frac- view encoding. tional Motion Estimation for Quad Full HD H.264/AVC Encoding,” Proc. IEEE Int’l. Conf. Multimedia Expo., 2009, pp. 9–12. CONCLUSION [13] L.-F. Ding et al., “A 212MPixels/s 4096×2160p Multi- view Video Encoder Chip for 3D/Quad HDTV Applica- In this article several issues in video encoder tions,” IEEE ISSCC Dig. Tech. Papers, 2009, pp. 154–55. design for 3DTV applications are discussed. First, the video coding standard development BIOGRAPHIES from 2D to 3D video is introduced. Among these PEI-KUEI TSUNG ([email protected])______received his standards, MVC, an extension profile in B.S. degree in electrical engineering and M.S. degree in H.264/AVC, provides the best coding efficiency electronics engineering from National Taiwan University, with a dramatically huge computation require- Taipei, Taiwan, in 2006 and 2008, respectively, where he is working toward his Ph.D. degree in electronics engineer- ment. Therefore, very large-scale integrated ing. His major research interests include stereo and multi- (VLSI) hardware acceleration is required to view video coding, motion estimation algorithms, view enable real-time applications. Moreover, the sys- synthesis algorithms, and associated VLSI architectures. tem analysis shows that the previous design LI-FU DING received his B.S. degree in electrical engineering, methods used in single video coding have dra- and M.S. and Ph.D. degrees in electronics engineering from matic hardware resource requirements and can- National Taiwan University in 2003, 2005, and 2008, not be employed directly. In order to deal with respectively. In 2009 he joined Taiwan Semiconductor these design challenges, solutions for each mod- Manufacturing Company as a principal engineer. His major research interests include stereo and multiview video cod- ule in the MVC encoder, including cache-based ing, motion estimation algorithms, and associated VLSI and predictor-centered IMDE, hybrid open-close architectures. loop intra prediction, and FPPDD CABAC, are proposed. After adopting all the proposed algo- WEI-YIN CHEN received his B.S. degree in electrical engineering and M.S. degree in electronics engineering from rithm and architecture optimizations, an MVC National Taiwan University in 2005 and 2008, respectively. single chip encoder is implemented under the In 2007 he was with MIT as a visiting graduate student. TSMC 90 nm process. By the proposed MVC His major research interests include super high definition encoder design, the target HD MVC specifica- and multiview video coding, associated VLSI architectures, tions can be supported with different view scala- high-level synthesis, and computer architecture. × bility from the 1920 1080p full HD three views TZU-DER CHUANG received his B.S.E.E. degree from the to 1280 × 720 HDTV seven views. Furthermore, Department of Electrical Engineering, National Taiwan Uni-

IEEE Communications Magazine • April 2010 85

versity in 2005. Now he is working toward his Ph.D. degree LIANG-GEE CHEN [S‘84, M‘86, SM‘94, F‘01] received B.S., in the Graduate Institute of Electronics Engineering, M.S., and Ph.D. degrees in electrical engineering from National Taiwan University. His major research interests National Cheng Kung University, Taiwan, in 1979, 1981, include the algorithm and related VLSI architectures of and 1986, respectively. He was an instructor (1981–1986) H.264/AVC, and scalable video coding. and an associate professor (1986–1988) in the Department of Electrical Engineering, National Cheng Kung University. YU-HAN CHEN received his B.S. degree from the Department In the military service during 1987 and 1988, he was an of Electrical Engineering, National Taiwan University in associate professor in the Institute of Resource Manage- 2003. He is currently pursuing his Ph.D. degree at the ment, Defense Management College. In 1988 he joined the Graduate Institute of Electronics Engineering, National Tai- Department of Electrical Engineering, National Taiwan Uni- wan University. His research interests include image/video versity. During 1993 to 1994 he was a visiting consultant signal processing, motion estimation, algorithm and archi- at the DSP Research Department, AT&T Bell Labs, Murray tecture design of H.264 video coders, and low-power and Hill, New Jersey. In 1997 he was a visiting scholar of the power-aware video coding systems. Department of Electrical Engineering, University of Wash- ington, Seattle. Currently, he is a professor at National Tai- PAI-HENG HSIAO received his B.S.E.E. degree from the wan University. Since 2004 he has also been the executive Department of Electrical Engineering, National Tsinh- vice president and general director of the Electronics Hua University, Hsinchu, Taiwan, in 2007. Now he is Research and Service Organization (ERSO) in the Industrial working toward his Master’s degree in the Graduate Technology Research Institute (ITRI). His current research Institute of Electronics Engineering, National Taiwan interests are DSP architecture design, video processor University. His major research interests include the algo- design, and video coding systems. He is a member of the rithm and architectures of video coding and neural sig- honor society Phi Tau Phi. He was the general chairman of nal processing. the 7th VLSI Design CAD Symposium. He is also the general chairman of the 1999 IEEE Workshop on Signal Process- SHAO-YI CHIEN [S‘99, M‘04] received B.S. and Ph.D. ing Systems: Design and Implementation. He has served as degrees from the Department of Electrical Engineering, an Associate Editor of IEEE Transactions on Circuits and National Taiwan University in 1999 and 2003, respective- Systems for Video Technology since June 1996 and as an ly. During 2003 to 2004 he was a research staff member Associate Editor of IEEE Transactions on VLSI Systems since at Quanta Research Institute, Tao Yuan County, Taiwan. January 1999. He has been an Associate Editor of the Jour- In 2004 he joined the Graduate Institute of Electronics nal of Circuits, Systems, and Signal Processing since 1999. Engineering and Department of Electrical Engineering, He served as a Guest Editor of the Journal of VLSI Signal National Taiwan University, as an assistant professor. Processing Systems for Signal, Image, and Video Technolo- Since 2008 he has been an associate professor. His gy in November 2001. He is also an Associate Editor of research interests include video segmentation algorithms, IEEE Transactions on Circuits and Systems II: Analog and intelligent video coding technology, perceptual coding Digital Signal Processing. Since 2002 he has also been an technology, image processing for digital still cameras Associate Editor of Proceedings of the IEEE. He received and display devices, computer graphics, and the associat- the Best Paper Award from the R.O.C. Computer Society in ed VLSI and processor architectures. He has published 1990 and 1994. From 1991 to 1999 he received Long-Term more than 120 papers in these areas. He serves as an (Acer) Paper Awards annually. In 1992, he received the Associate Editor for IEEE Transactions on Circuits and Best Paper Award of the 1992 Asia-Pacific Conference on Systems for Video Technology and Springer Circuits, Sys- Circuits and Systems in VLSI design track. In 1993 he tems, and Signal Processing, and served as a Guest Edi- received the Annual Paper Award of the Chinese Engineer tor for Springer Journal of Signal Processing Systems in Society. In 1996 he received the Outstanding Research 2008. He also serves on the Technical Program Commit- Award from NSC and the Dragon Excellence Award from tees of several conferences, including ISCAS, A-SSCC, and Acer. He was elected as the IEEE Circuits and Systems Dis- VLSI-DAT. tinguished Lecturer in 2001–2002.

86 IEEE Communications Magazine • April 2010

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INTEGRATED CIRCUITS FOR COMMUNICATIONS An Embedded 65 nm CMOS Baseband IQ 48 MHz–1 GHz Dual Tuner for DOCSIS 3.0

Francesco Gatta, Ray Gomez, Young Shin, Takayuki Hayashi, Hanli Zou, James Y.C. Chang, Leonard Dauphinee, Jianhong Xiao, Dave S.-H. Chang, Tai-Hong Chih, Massimo Brandolini, Dongsoo Koh, Bryan J.-J. Hung, Tao Wu, Mattia Introini, Giuseppe Cusmai, Ertan Zencir, Frank Singor, Hans Eberhart, Loke Tan, Bruce Currivan, Lin He, Peter Cangiane, and Pieter Vorenkamp, Broadcom Corporation

ABSTRACT range of cable plant conditions, ranging from high-power-loading scenarios requiring excep- An embedded CMOS digital dual tuner for tional linearity, to extremely-low-power condi- DOCSIS 3.0 and set-top box applications is pre- tions where linearity must be traded off for sented. The dual tuner down-converts a total of optimized noise performance. Although terres- ten 6 MHz Annex B channels or eight 8 MHz trial analog transmissions are being replaced Annex A channels, for a maximum data rate of with digital channels in many countries, legacy 320 Mb/s in Annex B and 400 Mb/s in Annex A analog channels still coexist with digital channels mode. The dual tuner exceeds all the stringent on the CATV medium. Because the analog chan- SCTE 40 specifications over the 48–1004 MHz nels are usually broadcast at significantly higher bandwidth, without using any external compo- power than the digital channels, the tuner nents or SAW filters. Enabling technologies are dynamic range requirements are substantial. a harmonic rejection front-end, a low-noise high- Besides robust operation under different signal frequency resolution PLL, and digital image loading scenarios, we desire an architecture that rejection. To our knowledge this is the first is easily adaptable to multichannel cable modem reported multichannel broadband tuner embed- DOCSIS 3.0 applications and can be used for ded in a DOCSIS 3.0 System on a chip imple- multituner digital video recorder (DVR) or per- mented in 65 nm pure digital CMOS technology. sonal video recorder (PVR) set-top box (STB) applications. MOTIVATION A cost-effective multichannel multituner solution can be achieved by integrating the tuner, The convergence of data, audio, and video over digital demodulator, MPEG decoder, memory, the Internet medium is resulting in ever increas- and processor core on a single system on chip ing data bandwidth needs. Due to customer (SoC), with considerable savings in power and demand and competition from other services, system complexity. cable television (CATV) service providers are This article reports a 65 nm complementary motivated to deliver data rates that far exceed metal oxide semiconductor (CMOS) dual tuner the capabilities of presently available cable net- embedded in a low-cost low-power DOCSIS 3.0 works. Data Over Cable Service Interface Speci- cable modem SoC that can demodulate up to 8 fication (DOCSIS) is the standard that regulates DS channels with frequency flexibility. In addi- high-speed data transfer over cable TV net- tion, although in the majority of cable plants the works. In order to compete with the higher highest spectrum frequency is 864 MHz, cable bandwidth offered, for example, by gigabit pas- providers are extending the CATV bandwidth to siver optical network (GPON) and very-high- 1 GHz to deliver more services. Therefore, we rate digital subscriber line (VDSL) services, designed the tuner to operate between 48 MHz cable providers have introduced the DOCSIS 3.0 and 1 GHz to allow deployment in all present standard [1]. DOCSIS 3.0 provides bandwidth and future extended cable plants. increase as well as additional customer flexibility The next section describes the tuner require- by bonding together multiple downstream (DS) ments, including the SCTE 40 requirements, in data or video channels. more detail. We then describe the challenges To increase the penetration of digital cable related to the tuner design for DOCSIS 3.0, services in cost-sensitive emerging markets, more while the following section describes the dual cost-effective and robust tuner integrated circuit tuner architecture. Circuit details are then pre- (IC) solutions are necessary. CATV tuners must sented, and the final section reports experimen- operate with good performance over a wide tal results.

DOCSIS 3.0 FREQUENCY ALLOCATION AND PERFORMANCE REQUIREMENTS The CATV radio frequency (RF) input frequency ranges between 54 and 864 MHz. The DOCSIS standard calls for 64-quadrature amplitude modulation (QAM) or 256-QAM modulated digital channels, occupying the same bandwidth as conventional analog TV channels. DOCSIS symbol rates are 5.36 MHz (corresponding to a 6 MHz RF bandwidth) for Annex B (United States) and 6.952 MHz (corresponding to an 8 MHz RF bandwidth) for Annex A (worldwide). 256-QAM modulation gives an effective data rate up to 38 Mb/s in DOCSIS 2.0. DOCSIS 3.0 allows a minimum data rate of 152 Mb/s by bonding any four channels in a 64 MHz contiguous RF bandwidth. Solu- tions that allow even more DS channel bonding and provide more flexibility in the allocated fre- Figure 1. Cable spectrum. quency spectrum are preferred by cable operators. For cable modem applications, the tuner must meet the DOCSIS specifications [1]. For STB desired channel, degrading SNR. Second-order applications, the requirements for the U.S. mar- and third-order distortion products (composite ket are summarized in the SCTE 40 standard [2]. second order [CSO] and composite triple beat Most customers currently require SCTE 40 com- [CTB]) from many different frequencies can fall pliance for all CATV applications; therefore, in on the desired signal and must be minimized by this work the tuner design has focused on meet- using highly linear RF blocks. However, the lin- ing the more stringent SCTE 40 specifications. earity cannot be obtained at the expense of SCTE 40 specifies a set of demodulation sce- noise figure (NF), leading to high dynamic range narios in terms of desired signal power levels, requirements. In a broadband RF receiver, par- analog adjacent channel interference (ACI) lev- ticular care must be taken to avoid spurious els, digital ACI levels, and cable plant loading noise pickup, in both the signal path and the with analog and digital channels. The standard synthesizer. This task is especially challenging in specifies channel impairments, such as incoming an SoC environment, where the digital noise phase noise, echoes, power line hum, and input sources are too numerous to avoid spurious signal-to-noise ratio (SNR), which represents the noise pick-up by proper frequency planning. noise generated by the CATV distribution system. To meet the stringent CATV requirements, In a worst-case 256-QAM scenario, the tuner and previously reported high-performance silicon demodulator must be able to operate error-free tuner designs have been RF standalone ICs iso- with a –12 dBmV desired channel with +16 dBc lated from the noisy SoC environment [3–5]. The analog ACI or +12 dBc digital ACI combined design in [5] uses a dual-conversion architecture, analog and digital loading of the CATV spec- while [3, 4] use a single-conversion low-IF archi- trum, 33 dB input SNR, echoes, hum, and added tecture, with integrated active filters [4] or a sys- phase noise. The demodulator requires about 29 tem in package (SiP) solution where dB SNR to operate error-free with margin, which high-selectivity filters are implemented in the means that the tuner itself must handle the above package substrate [3]. The first approach uses conditions with at least 32 dB SNR. The 64-QAM expensive external surface acoustic wave (SAW) low-power worst-case scenario is less stringent filters, and the long receive path results in high than 256-QAM because error-free video requires power consumption and overall system complexi- an SNR greater than 23 dB. ty. The low-IF SiP architecture reduces power consumption significantly, due to the external tracking filters that dramatically reduce the tuner TUNER DESIGN CHALLENGES AND dynamic range requirements. However, this PECIFICATIONS approach is not suitable for multichannel applica- S tions because of the difficulty in maintaining good A typical U.S. cable TV spectrum, shown in Fig. image rejection over many channels. Most impor- 1, includes legacy analog channels coexisting tant, both architectures are expensive for integra- with digital channels, with the analog channels tion in SoCs, given the use of bipolar CMOS usually between 54–550 MHz and the digital (BiCMOS) technology [5] and the prohibitive cost channels extending to 864 MHz. This broadband of the SoC package for SiP components [3]. signal spectrum imposes stringent requirements The tuner design is even more challenging for on tuner design parameters such as harmonic a DOCSIS 3.0 application due to the channel rejection, dynamic range, spurious pickup, and bonding requirement. Multiple tuners can be local oscillator (LO) purity. Harmonic rejection used to implement a DOCSIS 3.0 system, with means that the tuner must cope with signals each tuner down-converting a single channel. located at the harmonics of the LO, since they This provides full frequency flexibility at the can be down-converted in the mixing operation expense of system cost and power. On the other to the same intermediate frequency (IF) as the hand, a single tuner can down-convert the full 64

IEEE Communications Magazine • April 2010 89

Image rejection is 32 MHz enhanced digitally, -2 -1 0 +1 +2 taking advantage of Tuner 1 LO Tuner 1 the tuner integration LPF into the SoC, 2.5-20MHz Tuner 1 I path HRM LPF eliminating the need Tuner 1 ADC for part-to-part PGA VGA TIA 0,-5dB, DS AGC -2 -2 calibration. An HR -10dB,-15dB innovative PLL LO generation 1 architecture achieves HR -1 -1 low phase noise and Tuner 1 Q path low reference spurs RF PGA CAM-DS 0 0 while providing very RF IMC fine frequency RF splitter resolution. RSSI Tuner 2 Q path +1 +1

LO generation 2 HR +2 +2

HR Tuner 2 I path HR RFFE Tuner 2 Tuner 2

32 MHz -2 -1 0 +1 +2 Tuner 2 LO

Figure 2. Dual tuner top-level block diagram.

MHz RF bandwidth with reduced system power demodulation by the SoC, up to a maximum of and complexity, but no frequency flexibility since eight. Following the tuner, an eight-channel mul- all the channels need to be contiguous. tirate 64–256–1024-QAM downstream (DS) receiver separates and demodulates the eight UNER RCHITECTURE channels individually. This architecture does not T A require a SAW filter, allowing complete integra- This article presents a CMOS dual digital CATV tion in the SoC. Each tuner core included in this tuner for embedded SoC multichannel applica- RF front-end is designed to meet both DOCSIS tions that simultaneously provides frequency flex- and SCTE 40 standards. To suppress signals at ibility, low system cost and power, and superior the odd harmonics of the LO, a harmonic rejec- tuner performance [6]. Two tuners, each able to tion mixer (HRM) is used in combination with a select an agile 32 MHz frequency band, can highly linear RF-tracking filter. Image rejection down-convert ten 6 MHz Annex B channels, or is enhanced digitally, taking advantage of the eight 8 MHz Annex A channels. Figure 2 shows tuner integration into the SoC, eliminating the the top-level block diagram. The RF signal is need for part-to-part calibration. An innovative amplified by an external low noise amplifier phase locked loop (PLL) architecture achieves (LNA), which drives an internal splitter, followed low phase noise and low reference spurs while by the two baseband IQ tuners. Each tuner down- providing very fine frequency resolution. converts five 6 MHz Annex B channels to IF fre- The dual tuner core has been integrated in a quencies centered at DC with respect to the 65 nm CMOS technology DOCSIS 3.0 cable tuner local oscillator (channel 0), +6 MHz (chan- modem SoC that contains more than 32 million nel +1), +12 MHz (channel +2), –6 MHz (chan- gates. Embedding a noise-sensitive broadband nel –1), and –12 MHz (channel –2). For Annex tuner in the SoC is particularly challenging A, one tuner down-converts four 8 MHz chan- because the double data rate (DDR) clock/data nels to IF frequencies centered at +4 MHz and million instructions per second (MIPS) (channel +1), +12 MHz (channel +2), –4 MHz clock fall in the middle of the RF band. A signif- (channel –1), and –12 MHz (channel –2). Chan- icant amount of noise pickup occurs in the pack- nels +1 and +2 are located at the images of age leads and bond wires. By moving the LNA channels –1 and –2, respectively. The baseband off chip, the signal level is raised at the noisy IQ architecture acts as direct conversion for boundary, and pickup suppression requirements channel 0 and low-IF conversion for all the other are relaxed. The external variable gain LNA channels. Any or all channels can be selected for (VGLNA) provides up to 20 dB power gain with

90 IEEE Communications Magazine • April 2010

HR filter

LO1 IF OUT Flo 3Flo 5Flo 7Flo 9Flo 2

LO2

1 IF OUT Flo 3Flo 5Flo 7Flo 9Flo 1 LO3 1/3 LO1 1 1/5 1/7 1/9 1/7 -1 1/9 LO2 2 F 7F 9F Flo LO3 lo lo lo Flo3Flo 5Flo 7Flo 9Flo LO=LO1 + 2 LO2 + LO3 (a) (b)

CMFB TIA

+ IF OUT -

LOP_0 LOP_0 LOP_90 LOP_90 LOP_45 LOP_45 LON_0 LON_45 LON_90 RFP W/L RFN RFP 2W/L RFN RFP W/L RFN

(c)

Figure 3. Harmonic rejection mixer: a) harmonic folding; b) harmonic rejection concept; c) harmonic rejection mixer.

5 dB NF and a stable and high output third- TUNER RECEIVE PATH order intercept point (OIP3) over a 30 dB gain range thanks to an internal received signal The block diagram of the tuner receiver slice strength indicator (RSSI) [7]. plus splitter and RF front-end (RFFE) is shown in Fig. 2. A resistor ladder acts as impedance TUNER AGC matching and tapped RF attenuator that opti- In a cable environment the tuner input power is mizes the dynamic range for the two tuners. more tightly controlled than in a terrestrial envi- Each tuner uses an IQ baseband architecture ronment where few strong ACI are present. In with no external filters or SAW filters to mini- cable applications the ACI level is kept low, +16 mize external components. This brings design dBc for 256-QAM, but the number of channels is challenges that must be addressed, as we discuss very high. The high number of channels and in the following subsections. high-order QAM modulation call for a continuous automatic gain control (AGC) approach. For HARMONIC REJECTION FRONT-END this reason our work uses a mixed programmable In a conventional Gilbert cell mixer, the LO Gain Attenuator (PGA)-Variable gain amplifier switches are hard driven to improve linearity and (VGA) approach with 50 dB VGA range and 40 optimize noise figure. However, this generates dB PGA range. Two separate continuous AGC LO harmonics, where channels present at the loops are used, one at RF in the VGLNA and LO harmonics are folded on top of the desired one in the tuner baseband in the IF VGA. The channel, degrading SNR, as shown in Fig. 3a. By AGC of the VGLNA is controlled by a wideband using more LO phases and summing them with internal RSSI, and guarantees a constant power the right weighting, it is possible to approximate at the SoC tuner input. The desired channel a sinusoidal switching that does not contain har- power variations are compensated in the IF monics other than the fundamental [8]. This VGA, which is driven by the average power mea- design uses the 0°, 45°, and 90° LO phases to sured in the digital demodulator after the ADC. suppress the third and fifth harmonics (Fig. 3b). The RF AGC is optimized for the best noise fig- The harmonic suppression is limited by LO ure in the different loading scenarios, while the phase inaccuracies and gain mismatch, but care- IF AGC maximizes the ADC loading. ful design and the high-speed capabilities provid-

IEEE Communications Magazine • April 2010 91

In a cable Channel power environment the +1 -2 +2 tuner input power is -1 0 more tightly Channel power DC Frequency controlled than in a

terrestrial +1 I -2 +2 ADC environment where -1 0 I(n) LO_I few strong ACI are Imbalance QAM Flo Frequency canceller receiver present. In cable Q(n) applications the ACI ADC Q level is kept very low, LO_Q +16 dBc for 256-QAM, but the I + Σ I*(1-Wa) Σ I(n) number of channels -- is very high. Wa Wq

Q + Q(n) Σ Q*(1+Wa) Σ - + Wa I2 - Q2 Wq I * Q

Figure 4. Single-tap image rejection.

ed by our 65 nm CMOS process guarantee a noise density and hence the same NF for all pro- minimum harmonic rejection (HR) of 40 dB. In grammed cutoff frequencies. order to reject the seventh and ninth harmonics and guarantee a total rejection greater than 65 HARMONIC REJECTION MIXER dB for all the LO harmonics, the embedded The harmonic rejection mixer (HRM) schematic tuner incorporates an RF tracking filter in the is described in Fig. 3c. Three pseudo differential DOCSIS 3.0 SoC. Two source followers isolate pairs with resistive degeneration amplify the RF the two tuners, reducing the cross-LO leakage, signal with good NF and linearity. The three and provide a low-ohmic drive of the tracking transconductance stages are weighted 1:32:1 and filter. If the average frequency of the desired their outputs are multiplied in a Gilbert multipli- channels is below 330 MHz, the low-pass track- er cell by three phases of the LO (at 0°, 45°, and ing filter is selected; otherwise, the mixer is 90°). The current outputs of each mixer are directly connected to the splitter. This filter is summed together and injected into the virtual exposed to the full RF input power, thus requir- ground of a trans-impedance amplifier (TIA) ing extremely high linearity and low noise figure. that limits the voltage excursion on the mixer To reduce the filter input power, a wide band- output, thereby increasing linearity. A first-order width first-order pole precedes the filter and pole in the TIA feedback reduces the dynamic implements a programmable gain optimizing the range for the tuner back-end by attenuating dynamic range for the specific spectrum loading higher frequency adjacent channels, while the condition that is encountered. A third-order capacitor area is minimized by means of the vir- Butterworth filter is implemented with a com- tual ground operation. The TIA gain and first plex pole from a biquad and a real passive pole. order pole are programmable to cover single- An active RC approach is preferred over a Gm- channel and multichannel operation, and C approach for its higher linearity and ease of increase the overall tuner dynamic range. tuning. The noise figure constraint determines the resistor value, from which the capacitor size TUNER BASEBAND can be derived and hence the power dissipation. After the TIA, a fifth-order Butterworth low- To achieve the required linearity, the op-amp pass filter (LPF) serves as an anti-aliasing filter unity gain bandwidth needs to be higher than 3 and attenuates interferers that would saturate GHz. Such high unity gain bandwidth can be the ADC. The LPF bandwidth is programmable obtained using the high-speed devices available from 2.5 to 22 MHz to handle single-channel in our 65 nm CMOS process. The filter band- and multichannel applications. In the multichan- width ranges between 50 and 330 MHz, and is nel case, the filter must operate with five in- tuned with a bank of switched capacitors. Tuning band channels whose combined power can be up with capacitors allows the filter to keep the same to 22 dB higher than the minimum desired chan-

92 IEEE Communications Magazine • April 2010

nel, demanding very high in-band linearity to minimize cross-channel intermodulation and clipping. To optimize the trade-off between lin- LO_I earity and NF, the LPF is implemented as two 8 bit DAC 90-180MHz 2-4GHz Mixer PLL /4,/8, biquads plus a real pole in the TIA. The biquad DDFS DAC X 24 /16,/32,/64 architecture offers more flexibility in the filter design because the high-Q and low-Q biquads can be positioned based on the best trade-off XTAL Reference PLL LO_Q between linearity and noise. X 20 1000MHz Following the baseband LPF, a PGA and VGA set the ADC input power, avoiding satura- Tuner 2 tion of the ADC. A 20 dB continuous IF VGA tracks cable plant power variation and compen- sates for process, temperature, and voltage Figure 5. PLL block diagram. changes by keeping a constant input power at the ADC input. It maintains full ADC loading based on the multichannel signal, independent multiplied by the I-path and subtracted from the of the individual channel power values. The Q-path; similarly, Wq is multiplied by Q-path main challenge in this architecture is to keep the and subtracted from I-path. output linearity high under all loading scenarios, while not degrading the SNR for each individual PLL ARCHITECTURE channel. Note that low-power desired channels Demodulation of 256-QAM signals requires an can coexist with high-power wanted and unwant- in-band integrated phase noise better than 50 ed channels. Each tuner uses a dual 11-bit 175 dBc. A low in-band phase noise can be achieved Msamples/s pipeline 9.5 ENOB ADC to digitize by increasing the LO PLL bandwidth. However, the five-channel block. QAM demodulators also require frequency resolution in the tens of kilohertz, which demands a IMAGE REJECTION very low PLL bandwidth. This is the typical In traditional dual- or single-conversion low-IF trade-off between in-band phase noise, reference architectures, image rejection (IR) is implement- PLL spurs, and the PLL frequency step size pre- ed in the analog domain using external SAW fil- sent in classical integer-N PLLs. Fractional-N ters or by means of calibration of the analog PLLs have been commonly used in cable tuners imperfections during power-up [3, 5]. In our to widen the PLL bandwidth and obtain fine fre- design IR is enhanced in the downstream quency resolution [3, 5, 9], but they have the demodulator, while continuously receiving real potential to produce fractional spurs. In a dual stream data without need for power-up calibra- conversion architecture fractional spurs can be tion. tuned out of the desired channel by moving the In order to demodulate each of the five chan- up-conversion LO and the down-conversion LO nels present in the 32 MHz down-converted conveniently. This is not possible in a single- or band, the corresponding images need to be can- direct-conversion architecture such as ours. celled. The down-conversion of a block of five 6 Spurs due to digital noise pickup by the PLL are MHz channels with the imbalance canceller is also an issue. It is sometimes possible to avoid shown in Fig. 4. Due to imperfections of the IR, these spurs by careful frequency planning, but image channel information will leak into the this is very difficult in a complex SoC, where desired channel. For example, channel +1 would there are many asynchronous clock domains. leak on top of channel –1 and vice versa, degrad- The PLL for a CATV tuner must have very ing SNR. In order not to degrade the overall sys- low out-of-band (OOB) spurs to avoid folding of tem performance in the presence of all the the composite analog and digital loading. In this channel impairments, the SNR due to the image article we present a PLL architecture that com- must be higher than 45 dB for a 256-QAM mod- bines high frequency resolution with a wide loop ulated signal. Given that the maximum specified bandwidth, without introducing fractional refer- ACI from SCTE 40 is 16 dB for 256-QAM, the ence spurs (Fig. 5). A 50 MHz low-cost differen- IR must be higher than 61 dB. The finite IR is tial crystal oscillator clock is multiplied to mainly due to gain imbalances between the I and approximately 1 GHz by a fixed frequency refer- Q path and phase errors in the LO quadrature ence PLL. This serves as the reference for the generation. As a result of the IQ gain imbalance, 32-bit direct digital frequency synthesis (DDFS) the amplitudes of the I and Q outputs are differ- and an 8-bit digital-to-analog converter (DAC). ent, while the effect of an LO quadrature error The DDFS and DAC combination produces the is a non-zero product between I and Q. Follow- reference clock for an integer-N PLL that drives ing the baseband analog-to-digital conversion the down-conversion mixer. This architecture (ADC), two correction circuits cancel any gain enables sub-kilohertz LO frequency resolution and phase imbalance by driving to zero the gain while providing a high-frequency reference, error (I2 – Q2) and the phase error (I * Q). This allowing the PLL bandwidth to be increased. A removes any cross-correlation between the two larger loop bandwidth reduces phase noise, quadrature paths. In the gain imbalance can- improves power supply rejection ratio (PSRR), celler, the average difference between I2 and Q2 and shrinks loop filter size, thereby eliminating (Wa) is used to equalize the I and Q paths by the need for any external components. Given multiplying the I-path by (1 – Wa) and the Q- that the minimum reference frequency is higher path by (1 + Wa). To eliminate phase imbal- than 90 MHz, and the typical PLL bandwidth is ances, the product between I and Q (Wq) is around 500 kHz, reference spurs better than –75

IEEE Communications Magazine • April 2010 93

55 Pin=-12dBmV Pin=-6dBmV HR RFPE 50 Pin=+15dBmV

45 Reference PLL

Tuner 1 Tuner 2 Slicer SNR (dB) 35 Error free target (29dB) 30

25 04200 00600 800 1000 Frequency (MHz) (a) (b)

-50

-55

-60 2 -65 18A ADJ=+16dBc -70 +4dBmv SNR=48dB -75 ADJ=+10dBc -2dBmv -2dBmv SNR=41.5dB SNR=41.5dB -80 -12dBmv -85 SNR=34dB -12dBmv SNR=34.5dB -90 CH -2 CH -1 CH 0 CH +1 CH +2 -95

-100 Center 600 MHz 3.2 MHz Span 32 MHz (c) (d)

Figure 6. Dual tuner die photo and measured results.

dBc are achieved. Measurements indicate similar SNR tests have been performed with Internet traf- performance for all OOB spurs. An active anti- fic on. Since there is no frequency where the SNR alias filter following the DAC attenuates unwant- is substantially degraded due to the presence of ed spurs and the DAC images. The mixer PLL spurs, we can conclude that the tuner immunity to uses an LC-VCO that spans a frequency range signal path and PLL spurs is very high. between 2 and 4 GHz. The VCO output is divid- A DOCSIS 3.0 sample operation is described ed by 4/8/16/32 or 64 to cover the RF input spec- in Fig. 6c with five channels received simultane- trum, also generating the quadrature and the 0°, ously. The power for channel 0 and channel +2 45°, and 90° phases used in the HR mixers. To is –12 dBmV; for channels +1 and –1 it is –2 suppress phase modulation spurs in the VCO, dBmV (+10 dBc ACI); while for channel –2 it is the gain of the VCO is kept low. The 2 –4 GHz +4 dBmV (+16 dBc ACI). Channels +2 and –2 VCO range is implemented using a dual tank are images of each other, and they must be sepa- LC and an array of switched capacitors. The 1 rated before demodulation. Therefore, the SNR GHz reference PLL uses a low-noise ring-based of channels 0 and +2 is a good measure of the VCO with 6 MHz bandwidth. IR achieved. By noting that there is hardly a difference in SNR between channel 0 and channel XPERIMENTAL ESULTS +2, we can conclude that over-all IR perfor- E R mance is exceeding 60 dB. 1024 QAM modula- A micrograph of the dual tuner is shown in Fig. tion can provide a 25 percent throughput 6a. In Fig. 6b the measured 256-QAM slicer SNR improvement over 256 QAM modulation, fur- is shown for three input power levels: –12 dBmV ther increasing the DOCSIS 3.0 data rate at the (minimum power for SCTE 40), –6 dBmV (mid- expense of more tuner dynamic range. In Fig. 6d power), and +15 dBmV (high power). The mini- a constellation for an 847 MHz, +15 dBmV mum power SNR indicates the tuner NF and the input power clean channel with 47 dB SNR is margin from SCTE 40 error-free target. The mid- shown. Phase noise for the 1 GHz LO is –99 power SNR indicates the tuner dynamic range. dBc/Hz at 10 kHz offset, while it is better than The high-power SNR represents the tuner peak –122 dBc/Hz at 1 MHz offset. The in-band inte- SNR. The peak SNR drops at higher frequencies grated phase noise at 1 GHz is 0.2° root mean due to phase noise limitations. The single-channel square (rms) from 5 kHz to 10 MHz. PLL out-

94 IEEE Communications Magazine • April 2010

Gupta Tourret Stevenson This work ISSCC ’07 [9] JSCC ’07 [3] ISSCC ’07 [5] Cable modems for VoIP applications Input range 48–864 MHz 48–864 MHz 48–864 MHz 48–1000 MHz have different tuner NF 4–7 dB 5 dB 6–8 dB 5–7 dB requirements. In the case of an electrical 256 QAM sensitivity –22 dBmV power outage, the PN @ 10 KHz –90 dBc –90 dBc –85 dBc –100 dBc cable modem must be able to operate in CTB/CSO –53/–115 dBc –57/–57 dBc –65/–60 dBc –66/ –64 dBc battery backup IR 61 dB 62 dB 75 dB >62 dB mode and guarantee continuity of phone Max input power 44 dBmV 50 dBmV service. Power External filter NO YES (SiP) YES NO consumption for the cable modem SoC SoC integration NO NO NO YES and the tuner must Multiple channels NO NO — YES be minimized at the expense of DS channels 8 performance. Power (DOCSIS-VoIP) 540 mW, 1.8 V — — 800 mW, 2.5 V

1100 mW, 2.5 V LNA = 400 mW RX = 400 mW Tuner power (SCTE 40) — 780 mW, 3.3 V 1500 mW, 5 V PLL = 250 mW REFPLL = 50 mW ADC = 200 mW

Process 0.18 +m CMOS 0.25 +m SiGe (SiP) 0.35 +m SiGe 65 nm CMOS

5.7 mm2 (die) Area (one tuner) 25 mm2 7.25 mm2 5 mm2 9 mm * 9 mm (SiP)

Table 1. Performance summary and comparison with published literature.

of-band (OOB) and reference spurs are better cable loading is lower than SCTE 40. With than –75 dBc over the full cable band. With 135 reduced power consumption, the tuner meets +15 dBmV (–32 dBm) analog channels, the DOCSIS requirements over frequency with simi- measured CTB, CSO and cross modulation lar margins as SCTE40 operation. Finally, a per- (XMOD) are better than –66 dBc, –64 dBc, and formance summary with a comparison with the –60 dBc respectively. state of the art is shown in Table 1. The tuner can operate in two power modes: SCTE 40 mode when used in set-top box appli- ONCLUSIONS cations and DOCSIS mode when it is used in a C cable modem application. The SCTE 40 low An embedded CMOS digital dual tuner for power worst-case condition for –12 dBmV input DOCSIS 3.0 and set-top box applications has power, +16 dBc ACI, 33 dB cable SNR, and been presented. The dual tuner can down-con- cable plant loading is met with 1.5 dB worst case vert a total of ten 6 MHz Annex B channels or minimum margin. In a fully loaded test like eight 8 MHz Annex A channels, for a maximum SCTE40, PLL spurs can fold all the high power data rate of 320 Mb/s in Annex B and 400 Mb/s ACI on top of the desired channel. Good margin in Annex A mode. The dual tuner exceeds all over the specifications testify for the purity of the stringent SCTE 40 specifications over the the tuner LO. 48–1004 MHz bandwidth, without using any Cable modems for VoIP applications have external components or SAW filters. Enabling different tuner requirements. In the case of an technologies are a harmonic rejection front-end, electrical power outage, the cable modem must a low-noise high-frequency-resolution PLL, and be able to operate in battery backup mode and digital image rejection. guarantee continuity of phone service [10]. Power consumption for the cable modem SoC ACKNOWLEDGMENTS and the tuner must be minimized at the expense The authors would like to thank J. Brannon, S. of performance: typical ACI levels are lower Freville, R. Nguyen, R. Whitehead, and D. than 10 dBc, cable input SNR is 34 dB, and McMullin for their support.

IEEE Communications Magazine • April 2010 95

REFERENCES engineering from UCLA in 1996. Since 1996 he has been with Broadcom Corp., mostly designing CMOS integrated [1] CableLabs, “Data Over Cable Service Interface Specifica- tuners for DBS satellite, QAM cable, and fiber optic (MoCA) tions, DOCSIS 3.0, Physical Layer Specification,” CM-SP- applications. He is currently a manager of engineering at PHYc3.0-I07-080522, May 22, 2008. Broadcom focusing on research and development of cur- [2] SCTE Eng. Committee, “Digital Cable Network Interface rent and future generation tuners for QAM and MoCA set- Standard,” ANSI/SCTE 40, 2004. top box and modem SoCs. [3] J. R. Tourret et al., “SIP Tuner with Integrated LC Track- ing Filter for Both Cable and Terrestrial TV Reception,” TAKAYUKI HAYASHI received B.A.Sc. and M.A.Sc. degrees in IEEE J. Solid-State Circuits, vol. 42, no. 12, Dec. 2007, electrical engineering from the University of Toronto, pp. 2809–21. Ontario, Canada, in 1995 and 1997, respectively. From [4] J. van Sinderen et al., “A 48 MHz to 860 MHz Digital 1997 to 2000 he was with ATI Technologies, Thornhill, Cable Tuner IC with Integrated RF and IF Selectivity,” Ontario, working on the development of ADC for video IEEE ISSCC Dig. Tech. Papers, Feb. 2003, pp. 444–45. applications. In 2000 he joined Broadcom Corp., where he [5] J. M. Stevenson et al., “A Multi-Standard Analog and is currently a principal design engineer. His research inter- Digital TV Tuner for Cable and Terrestrial Applications,” ests are in analog and mixed-signal circuit design for com- IEEE ISSCC Dig. Tech. Papers, Feb. 2007, pp. 210–11. munication systems. [6] F. Gatta et al., “An Embedded 65 nm CMOS Baseband IQ 48 MHz–1 GHz Dual Tuner for DOCSIS 3.0,” IEEE J. HANLI ZOU received his B.S. degree in electronic engineering Solid-State Circuits, vol. 44, no. 12, Dec. 2009, pp. from Tsinghua University, Beijing, China, in 1996, and his 3511–25. M.S. and Ph.D. degrees in electrical engineering from UCLA [7] D. Manstretta et al., “A Highly Linear Broadband Vari- in 2000 and 2003, respectively, with a focus on integrated able Gain LNA for TV Applications,” IEEE CICC ‘07, circuits and systems for wireless broadband communica- Sept. 2007, pp. 531–34. tion systems. From 2001 to 2003 he worked as senior ASIC [8] J. Weldon et al., “A 1.75 GHz Highly Integrated Nar- designer at Innovics Wireless Corporation, Los Angeles, Cal- row-Band CMOS Transmitter with Harmonic Rejection ifornia, designing baseband chipsets for a diversity enabled Mixers,” IEEE J. Solid-State Circuits, vol. 36, Dec. 2001, WCDMA transceiver. Since 2003 he has been with the pp. 2003–15. Broadband VLSI Group, Broadcom Corp. as a principal sci- [9] M. Gupta et al., “A 48-to-860 MHz CMOS Direct Con- entist, working on advanced transceiver chip design for version TV Tuner,” IEEE ISSCC Digest Tech. Papers, Feb. cable, satellite, home networking, and terrestrial digital TV 2007, pp. 206–7. and set-up box. His research interest includes system [10] CableLabs, “PacketCable 1.5 Specifications MIBs design and VLSI implementation for high-speed communi- Framework Specification,” PKT-SP-MIBS1.5-I02-070412, cation, with an emphasis on digital compensation for Apr. 12, 2007. RF/analog front-end impairments, synchronization, channel estimation, equalization, and diversity processing.

ADDITIONAL READING JAMES Y.C. CHANG received his B.Sc. degree (magna cum [1] ITU-T G.984.1, “Series G: Transmission Systems and laude) from UC Irvine, and his M.Sc. and Ph.D. degrees from Media, Digital Systems and Networks, Gigabit-Capable UCLA in 1990, 1992, and 1998, respectively, all in electrical Passive Optical Networks (GPON): General Characteris- engineering. He was a co-recipient of the Best Paper Award tics,” Mar. 2008. at the 1995 ESSCIRC, and the Jack Raper Award for Out- [2] ITU-T G. 993.2, “Series G: Transmission Systems and standing Technology Directions at ISSCC ’97. He received the Media, Digital Systems and Networks, Very High Speed Outstanding Ph.D. Student Award from UCLA for the year Digital Subscriber Line Transceivers 2 (VDSL2),” Feb. 1997–1998. He is currently with Broadcom Corp. developing 2006. cable and satellite set-top-box SoC embedded tuners. He is a [3] I. Vassiliou et al., “A 65 nm CMOS Multistandard, named inventor on seven issued patents. Multiband TV Tuner for Mobile and Multimedia Appli- cations,” IEEE J. Solid-State Circuits, vol. 43, no. 7, July LEONARD DAUPHINEE earned a B.Eng. in electrical engineering 2008, pp. 1522–33. from Dalhousie University, Halifax, Canada, in 1987. From 1987 until 1989 he designed underwater data telemetry products at Vemco Ultrasonics. He returned to Dalhousie BIOGRAPHIES University to earn an M.A.Sc. in electrical engineering in 1991, specializing in real-time DSP architectures. From 1991 FRANCESCO GATTA ([email protected])______received his Laurea until 1993 he was the engineering manager of RF commu- and Ph.D. degrees in electrical engineering from the Univer- nications design at the Applied Microelectronics Institute. sity of Pavia, Italy, in 1998 and 2001, respectively. His Ph.D. He began doctoral studies at Carleton University, Ottawa, research focused on CMOS highly integrated receivers for Canada, with a focus on RFIC design in 1993. In 1998 he UMTS applications and low-power CMOS LNA. From 2001 to joined Broadcom Corporation as a staff scientist working on 2002 he was with Valence Semiconductor working on CMOS broadband tuner products and earned his Ph.D. from Car- GPS products. Since 2002 he has been with Broadcom Cor- leton University in 2003. He is presently the senior engineer- poration, Irvine, California, in the Analog-RF Group where he ing manager of RF tuner development at Broadcom and is has been working on PLL for SERDES applications, CTF for named as inventor on 29 issued or filed U.S. patents. hard disk drives, and tuners for cable and satellite applications. Currently he is leading the development of all the JIANHONG XIAO [S‘04] received his B.Sc. degree from the CATV and DTV CMOS integrated tuners. His main interests Department of Computer Science and Technology, Peking are in RF CMOS design, tuner architectures, and broadband University, China, in 2001, and his Ph.D. degree from Texas systems. He is the named inventor of three U.S. patents. A&M University in 2007. He worked at Analog Devices as design engineer intern in summer and fall 2004 and sum- RAY GOMEZ received his B.S degree in biomedical engineering mer 2005. He joined Broadcom as a staff scientist in 2007. from Case Western Reserve University in 1981, his M.S.E.E His main research interests cover analog and RF front-end degree in electrical engineering from Stanford University in design for broadband communication systems. 1982, and his Ph.D. degree from the University of California, Los Angeles (UCLA) in 1993. He worked at TRW, Inc., Redon- TAI-HONG CHIH received his diploma in electrical engineering do Beach, California, from 1982 to 1986, where he designed from National Tsing-Hua University in 2001, and his M.S degree high-performance frequency synthesizers. His research at in electrical and computer engineering from Carnegie Mellon UCLA, from 1986 to 1993, involved analog CMOS integrated University in 2005. He has worked in the RF tuner department circuits for disk-drive read channels. From 1993 to 1995 he at Broadcom since 2005. His interests include RF/analog circuits was a member of the disk drive read channel group at Cirrus and tuner/broadband communication systems. Logic, Austin, Texas. He joined Broadcom Corp. in 1995, where he has focused on CMOS RF circuits for cable and DAVE (SUNG-HSIEN) CHANG received B.S. and M.S. degrees in broadcast television tuners, DBS satellite set-top box tuners, communication engineering from National Chiao-Tung Uni- and, more recently, MoCA home multimedia networking. He versity, Hsin Chu, Taiwan, R.O.C., in 1992 and 1994, was named a Broadcom Fellow in 2006 for his contributions respectively. He received his Ph.D. degree in electrical engi- to tuner design, and has over 30 issued patents. neering from the UCLA, where he was working on microwave and millimeter-wave circuits in 2000. In 2000 YOUNG J. SHIN received his B.S. degree in electrical engineer- he joined Broadcom Corp., where he is involved in designing and computer science from the University of California ing integrated circuits for CMOS standalone and SoC (UC) Berkeley, in 1994 and his M.S. degree in electrical tuners for cable, set-top box, and satellite applications.

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MASSIMO BRANDOLINI received his Laurea (summa cum laude) cable, satellite receivers, and MoCA transceivers. His inter- and Ph.D. degrees in electrical engineering and computer ests include analog and RF IC design for broadband and science from the University of Pavia in 2002 and 2006, wireless communications. respectively. During his Ph.D., he worked on analog and RF ICs for wireless communications in CMOS and BiCMOS FRANK W. SINGOR received his B.A.Sc. degree in electrical technologies, with focus on RF front-ends for cellular appli- engineering from the University of Western Ontario, Cana- cations and multistandard radios. In 2003 he was with da, in 1991 and his M.A.Sc. degree from the University of Agere Systems, Allentown, Pennsylvania, as an internship Toronto, Ontario, Canada in 1994. In 1994 he joined the student, working on the design of a fully integrated CMOS Data Converter Group at Maxim Integrated Products, Sun- FM transmitter. He joined Broadcom Corp. in January nyvale, California. In 1999 he joined Broadcom Corp., 2006, where he is a senior staff scientist working on highly working in the Mixed Signal Group, and presently is man- integrated tuners for cable, satellite and MoCA systems. He aging Broadcom RF Tuner Development, Austin, Texas. is a co-recipient of the IEEE Journal of Solid-State Circuits 2003 Best Paper Award and the IEEE Symposium on VLSI HANS EBERHART received B.S. and M.S. degress in electrical Circuits 2005 Best Student Paper Award. engineering from the University of Pennsylvania, Philadel- phia, in 2000 and 2001, respectively. Between 2002 and JUO-JUNG HUNG received B.S. and M.S. degrees in electrical 2004 he was working toward his Ph.D. in electrical engi- engineering from National Taiwan University, Taipei, neering at UCLA. In 2004 he joined Broadcom Corp., where R.O.C., and his Ph.D. degree in electrical engineering from he is involved in analog and mixed-signal circuit design. the University of Michigan, Ann Arbor, where he was involved with the development of SiGe RFIC and RF micro- LOKE K. TAN received his B.S. degree from the University of electromechanical systems (MEMS) for microwave and mil- Houston, Texas, in 1987, and his M.S. and Ph.D. degrees limeter-wave applications. He is currently a senior staff from UCLA in 1992 and 1995,respectively, all in electrical design scientist with Broadcom Corp., where he has engineering. He was a consultant to PairGain Technologies focused on CMOS analog and RF circuits for satellite, cable, in 1992. Since 1993 he has been with Broadcom Corp., and terrestrial television receivers. where he works in the Communications Systems and IC Design Group. He has been involved in the design of QAM DONGSOO KOH [S‘89, M‘98] received B.S. and M.S. degrees transceivers for HDTV applications. His interests include in electronics engineering from Sogang University, Seoul, digital signal processing, digital communications, and high- Korea, in 1989 and 1991, respectively, and a Ph.D. degree performance CMOS circuit design. He received the 1995 in electrical engineering from UCLA in 1997. From 1997 to Best Paper Award from the IEEE Journal of Solid-State Cir- 1999 he was with BethelTronix, Inc, Cerritos, California, cuits for the paper entitled “A 200 MHz Quadrature Digital where he developed RF ICs for cordless phones and GPS Synthesizer/Mixer in 0.8 mm CMOS.” systems. From 1999 to 2006 he was with Skyworks Solu- tions, Inc. (formerly Conexant Systems, Inc.), Irvine, Califor- LIN HE received her Ph.D. degree from the University of nia, where he worked on RF IC designs for various mobile Pennsylvania in 2005. From 2005 to 2007 she was with standards including CDMA 2000 and GSM/EDGE. Since Sarnoff Corporation, Princeton, New Jersey. She joined 2006 he has been with Broadcom Corp. His work has Broadcom Corp. in 2007 as a senior staff scientist. She is focused on RF tuner development for broadband commu- currently involved with system design for broadband com- nication products. munication systems.

Tao Wu received his B.S. degree in mechanical engineering BRUCE CURRIVAN is technical director, Broadband Communi- from Harbin Institute of Technology, China, in 1992, and his cations at Broadcom Corp., where he develops advanced M.S. degree in electrical engineering from the University of modem architecture. He holds a B.S. from Cornell Universi- Arizona in 1999. Currently, he is with Broadcom’s RF tuner ty and an M.S.E. from Princeton University, both in electri- group and involved in RF and mixed signal circuit designs for cal engineering and information sciences. Prior to broadband applications. From 2005 to 2006 he worked for Broadcom he worked at RCA Astro-Electronics Division, Skyworks. From 2000 to 2005 he worked at Stanford Telecommunications, Inc., and Wavespan Corpo- Motorola/Freesclae, Libertyville, Illinois, where he was involved ration. He served as Chairman of the IEEE 802.14 Cable in RF and mixed signal designs for wireless applications. Modem Physical Layer Subgroup, and was a major contributor to the DOCSIS specifications. He is the author of many Mattia Introini received his Laurea degree in electrical engi- designs, papers, book chapters, and patents in the areas of neering and computer science from the University of Pavia modem design and adaptive equalization. in February 2006. He joined STMicroelectronics in 2006 as an analog IC designer; during this period he worked on PETER CANGIANE received Bachelor’s and Master’s of Science analog and RF ICs for hard disk drive applications in CMOS degrees in electrical engineering from Polytechnic Institute technology, with focus on the read channel RF front-end. of New York in 1986 and UCLA in 1988, respectively. He In October 2006 he joined Broadcom Corp. as a design was with TRW Corporation from 1986 until 2000, where engineer. He has been working on highly integrated tuners he specialized in multirate digital signal processing. Since for cable, satellite, and MoCA systems. 2000 he has been with Broadcom Corp.’s Broadband Cable Business Unit. He is the named inventor of one U.S. patent. GIUSEPPE CUSMAI [S‘05] received his Laurea and Ph.D. degrees in electrical engineering and computer science PIETER VORENKAMP received his M.S. degree in electrical engi- from the University of Pavia in 2003 and 2007, respective- neering from Twente University, Enschede, The Nether- ly. His Ph.D. research was focused on CMOS and bipolar lands. From 1989 to 1996 he was with Philips Research TX/RX front-ends for WPAN communications (UWB). In Laboratories, Eindhoven, The Netherlands, researching 2005 he was with National Semiconductor, Santa Clara, high-speed data converters in BiCMOS processes. From California, as an internship student, working on a CMOS 1996 to 1997 he was with Philips Semiconductors, Caen, low-power highly integrated transmitter for Zigbee. Since France, responsible for the development of high-speed January 2007 he has been with Broadcom Corp., where he data acquisition systems for video and instrumentation develops highly integrated CMOS tuners for cable and applications. In 1997 he joined Broadcom Corp., where he satellite systems. has held progressively senior engineering management positions. In 1999 he managed the Analog and RF Micro- ERTAN ZENCIR received B.Sc. and M.Sc. degrees in electrical electronics group in Irvine, California, responsible for the and electronics engineering from Middle East Technical analog part of all mixed-signal chips for application in digi- University, Ankara, Turkey, in 1995 and 1997, respectively, tal communication systems, ranging from high-fidelity and a Ph.D. degree in electrical engineering from Syracuse audio front-ends to RF tuner subsystems for cable and TV University, New York, in 2003. Between 2004 and 2005 he applications. In 2008 he managed Broadcom’s Power Man- worked as an assistant professor in the Department of agement Business Unit and successfully introduced the first Electrical Engineering, University of Wisconsin-Milwaukee. standalone Power Management and Energy Management From 2005 to 2006 he was with the RFIC design team of product line for mobile and other battery powered SoCs Nokia Mobile Phones, San Diego, California, as a senior into the market. Most recently he is responsible for opera- RFIC design engineer, where he specialized in SiGe BiCMOS tions engineering, including foundry engineering, product cellular RF transceiver IC design for CDMA2000. Since 2006 engineering, product test, and assembly within Broadcom’s he has been with the RF Tuner Development Department Operations and Central Engineering organization. He is an of Broadcom Corp., where he is currently a senior staff author of many international publications and is a named design scientist developing analog and RF CMOS ICs for author of almost 50 U.S. patents.

IEEE Communications Magazine • April 2010 97

INTEGRATED CIRCUITS FOR COMMUNICATIONS Integrated Electronic System Design for an Implantable Wireless Batteryless Blood Pressure Sensing Microsystem

Peng Cong, Medtronic Inc. Wen H. Ko, Case Western Reserve University Darrin J. Young, University of Utah

ABSTRACT monitoring. Therefore, a miniature lightweight long-term blood pressure sensing implantable A wireless, batteryless, less invasive blood pres- microsystem with wireless data telemetry and sure sensing microsystem based on an instrument- adaptive RF powering capability is highly desired circular cuff has been developed for advanced able to capture the vital signs of a free roaming biological research. The proposed sensing tech- small laboratory animal housed in its home cage, nique avoids vessel penetration and substantially as depicted in Fig. 1. minimizes vessel restriction due to the soft cuff elasticity. The integrated electronic system design is presented with emphases on the design trade-off A LESS INVASIVE BLOOD PRESSURE and system considerations. The measurement ONITORING YSTEM results demonstrate full functionality of the M S microsystems with real-time high-fidelity blood A 3D illustration of a wireless, batteryless, less pressure sensing capability under wireless data invasive implantable blood pressure monitoring telemetry and adaptive RF powering conditions. system is illustrated in Fig. 2. The system employs an instrumented elastic cuff wrapped around a INTRODUCTION blood vessel, which is not shown in the picture, to sense real-time blood pressure waveforms. The Cardiovascular diseases are the number one elastic cuff is made of bio-compatible silicone cause of death and disability in the United States material and is filled with low-viscosity silicone and most European countries. Long-term in vivo oil with an immersed micro-electro-mechanical blood pressure monitoring is critical for treating system (MEMS) pressure sensor and integrated cardiovascular disease and hypertension. Recent- electronic system. The MEMS sensor measures ly, DNA sequencing of small laboratory animals the pressure waveform in the cuff coupled from together with real-time monitoring of blood pres- the expansion and contraction of the vessel. A sure as well as other vital signals has become a rigid silicone isolation ring is used to decouple critical research tool to identify genetic suscepti- the sensing cuff, which is located at the structural bility to diseases and to potentially develop new center, from environmental variations in the ani- treatment methods [1]. However, the small blood mal’s body. Because of the softness of the sens- vessel size of those animals, less than 1 mm in ing cuff’s outside wall, the pressure inside the diameter for major arteries, introduces a signifi- sensing cuff is susceptible to environmental varia- cant design challenge for the blood pressure tions, such as muscle and tissue movement, with- monitoring microsystem; there is no good solu- out the isolation ring. The isolation ring is tion for its long-term in vivo monitoring to date. designed so that an air cavity between the isola- The most common technique used in small tion ring and the sensing cuff’s outside wall is laboratory animal monitoring relies on an invasive formed upon completion of the fabrication pro- catheter-tip transducer, which requires a complex cess. As a result, the sensing cuff’s outside wall surgical procedure and could cause increased can move freely, responding to the blood vessel blood pressure, blood clotting, and reduced sensi- pressure waveform. In the figure an additional tivity over time. Furthermore, discrete electronics thin metal layer wraps around the isolation ring are typically employed to implement the implant for further suppression of environment varia- system, resulting in a large form factor with exces- tions. The overall structure has a radius of 3.2 sive power dissipation, which in turn calls for a mm and a width of approximately 4 mm to estab- bulky ferrite-based radio frequency (RF) coil for lish an adequate contact area with a blood vessel external RF powering or battery recharging, thus to be inserted in the middle of the cuff through limiting the accuracy of the measured biological the opening/closing slot. A surgical suture will be signals due to post-implant trauma for long-term applied to secure the cuff position after vessel

External RF powering Data receiving antenna A wireless powering and data acquisition system with an adaptive power control capability is

B.P. waveform required to provide a sufficient and stable energy to power the implant electronics in Animal cage a varying magnetic RF powering coil field. The RF-DC

RF power converter also Blood pressure monitoring system extracts clock information from the RF powering signal. Figure 1. In vivo real-time wireless batteryless blood pressure monitoring microsystem.

insertion. The radius of the sensing cuff’s inside signal. The output of the C/V converter is then dig- wall is designed to be approximately 0.5 mm with itized by an ADC for wireless data transmission. an outside sensing cuff wall radius of approxi- Wireless RF powering and data telemetry are also mately 0.9 mm, thus adequate for laboratory ani- incorporated in the microsystem to eliminate the mals with an artery diameter of around 1 mm. need for external wire connections and any bulky The silicone sensing cuff can be fabricated by a battery. The microsystem can therefore be used to conventional machining and molding process [2]. monitor freely moving small laboratory animals to The measured waveform represents a down- obtain reliable measurements without stress- scaled version of the vessel blood pressure wave- induced distortion due to wire connections or large form with a typical scaling factor of 10 percent system size. RF powering has been widely used for and is processed by a nearby low-power integrated biomedical implants, where both transmitting and electronics system exhibiting a dimension of receiving units are properly placed at a fixed dis- approximately 2 × 2 × 3 mm3, consisting of MEMS tance from each other with a constant RF power sensor interface circuitry, an analog-to-digital con- coupling coefficient. However, in this research the verter (ADC), and a system configuration and receiving unit is implanted inside a freely moving control unit, followed by wireless data telemetry to laboratory animal, resulting in a continuously an external receiver. Post-implant calibration can changing RF power coupling. Therefore, a wireless be performed to reconstruct the vessel blood pres- powering system with an adaptive power control sure waveform from the measured data. An adap- capability is required to provide a sufficient and tive RF-DC power converter is incorporated to stable energy to power the implant electronics in a provide sufficient and stable energy to the system varying magnetic field. The RF-DC power convert- implanted in an untethered animal as shown in er also extracts clock information from the RF the overall system diagram in Fig. 3. The spiral powering signal. An on-chip power sensor is coil for RF powering is located outside the cuff designed to detect the received RF power level with sealed feed-through connections to the elec- and generates a 1-bit power-level feedback signal. tronics. The proposed sensing technique avoids The 1-bit power-level feedback signal together with vessel occlusion, bleeding, and blood clotting asso- the digitized blood pressure information is then ciated with the conventional catheter-tip-based transmitted to an external receiver by an on-chip approach. Furthermore, the sensing cuff is made oscillator-based frequency shift keying (FSK) trans- of soft silicone material. The restrictive effect on mitter with an off-chip inductor achieving the func- the vessel is therefore substantially minimized, tion of an antenna. The high-Q off-chip inductor is thus making it suitable for long-term monitoring. employed for low power dissipation. The received blood pressure information is used for real-time blood pressure monitoring. The 1-bit power-level INTEGRATED ELECTRONIC feedback signal is used to control an external YSTEM ESIGN power amplifier supply voltage to realize adaptive S D RF powering capability. System integration of integrated electronics and To realize a functional system, the electronics micro-fabricated sensors can provide a unique should be properly designed to achieve performance solution to realize an implantable microsystem requirements, such as pressure resolution, system with small size, light weight, and reliable sensing dynamic range, on-chip DC power level via RF capability. A MEMS capacitive pressure sensor is powering, sensor data transmission rate, and wire- designed and incorporated in the sensing cuff to less communication range. Miniaturization can be convert blood pressure information to capacitance achieved by integrating various building blocks onto variation. A capacitance-to-voltage (C/V) converter a single chip as well as keeping individual building is thus required in the integrated electronic system blocks small by employing an optimal architecture. to convert the capacitance variation to a voltage In addition, each building block should be designed

IEEE Communications Magazine • April 2010 99

digitization. The C/V converter needs to be Metal isolation ring designed for a sensing resolution of 100 aF over a 1 kHz bandwidth and an allowed overall full-range mm capacitance variation of 200 fF, which corresponds 3–5 Silicone isolation Coil for RF powering to a dynamic range of 11 bits. An automatic offset ring cancellation scheme is designed as shown in Fig. 3 3.2 mm to allow a single-ended pressure sensor with a wide Sensing cuff range of nominal capacitance value to be used, outside wall thus greatly simplifying the MEMS fabrication process; it can also effectively suppress the output offset voltage. During the initial phase of the circuit operation, the digitally controlled reference capacitor array at the amplifier input is cycled through to MEMS pressure sensor find a reference capacitance closely matched to the with Interface Electronics immersed in silicone oil sensor nominal capacitance. 1/f noise from input transistors of a front-end amplifier used in the C/V converter is typically the Figure 2. 3D configuration of the blood pressure sensing microsystem. dominant noise source, and can effectively be sup- pressed by correlated double sampling (CDS) or chopper stabilization techniques [3, 4]. The CDS immune to interference for robust performance. A technique, which was originally introduced to fully differential architecture is used for the sensor reduce the noise produced in charge-coupled interface electronics and ADC design for adequate devices, is an effective method to suppress low-fre- common-mode signal rejection. A low-power design quency noise, DC offset, and charge injection is important for implantable systems, where the effects in switched-capacitor circuits. A typical CDS power source is highly limited. A low-power design amplifier samples the amplifier output voltage twice can be achieved by choosing proper system architec- per clock cycle: first in a reset phase and second in tures and circuit implementations. A capacitive pres- an evaluation phase. The offset and low-frequency sure sensor, instead of a piezoresistive pressure noise, such as 1/f noise, at these two sampling sensor, is selected for the overall microsystem design instances are nearly constant due to a relatively to minimize power dissipation. Interface electronics high sampling frequency. Therefore, they are highly are designed to operate in a weak inversion region correlated, and can be eliminated by performing a for further power reduction. It is difficult to provide subtraction operation between the two samples. a high supply voltage for wireless and batteryless The sampling frequency needs to be designed much microsystem operation. Therefore, low-voltage higher than 1/f noise corner frequency with a typical design techniques become essential. For a 1.5 +m ratio of 10. A disadvantage of CDS is that the complementary metal oxide semiconductor (CMOS) uncorrelated thermal noise is doubled due to the process selected for the prototype design with VTP double sampling. The amplifier must be designed and VTN of approximately –1 V and 0.7 V, respec- to meet the thermal noise requirements. tively, a 2 V power supply level is chosen as a trade- Chopper stabilization is another commonly off between circuit design complexity and RF used technique to reduce offset and low-frequency powering constraints. The 2 V power supply will be noise in precision analog circuit design. First, the generated by an on-chip RF-DC power converter. A sensor information is modulated to a high fre- 2.5 V supply will also be generated to control the quency by a stimulation clock, where the stimula- MOS field effect transistor (MOSFET) without dis- tion frequency needs to be much higher than 1/f sipating any DC power. The design trade-off of the noise corner frequency. The modulated sensor sig- MEMS pressure sensor, C/V converter, cyclic ADC, nal is then mixed by a clock exhibiting the same and transmitter is presented in detail in this section. frequency as the stimulation frequency, followed The adaptive RF-DC powering will be covered by by a low-pass filter to obtain the original sensor other papers. signal. In this process the 1/f noise and DC offset from the charge amplifier are modulated to the MEMS CAPACITIVE PRESSURE SENSOR stimulation frequency by the mixer and then elimi- The MEMS capacitive pressure sensor was nated by the low-pass filter. A comparison designed for the prototype microsystem design between chopper stabilization and CDS tech- due to its miniature size, high sensitivity, low niques shows that CDS excels in a number of temperature dependence, zero DC power dissi- aspects for this application. First, switched-capaci- pation, and time stability. The fabricated sensor tor-based CDS is more compatible with a sampled exhibits dimensions of 0.4 × 0.5 × 0.4 mm3 with a data system. Second, instead of being modulated measured nominal capacitance value of approxi- to a high frequency by the chopper stabilization mately 2 pF and a sensitivity of approximately technique, the DC offset and 1/f noise are elimi- 0.8 fF/mmHg [2]. The device size is adequate to nated by the CDS technique at the amplifier out- be enclosed in the blood pressure sensing cuff. put, thus increasing the allowable signal swing range, which is critical for the low supply voltage CORRELATED DOUBLE SAMPLING C/V design. Finally, chopper stabilization typically CONVERTER WITH AUTOMATIC OFFSET requires a mixer and a low pass filter, which result CANCELLATION SCHEME in additional power consumption and silicon area. There are three noise contributors for the Interface electronics are required to convert sensor pre-amplifier circuit. The first contributor is the capacitance variation, which represents the blood switch thermal noise associated with the switches pressure information, into analog voltage prior to connected to the left plates of the sensor capaci-

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Integrated circuit Voltage doubler VHIGH VLOW L2 C2 On-ship DC voltage CLK regulators Adaptive VDD RF power input extraction Digital Skin B.P. and 4 MHz VDD_Analog_2V 2.5V Class-E Power-level sensor power-level VDD_Digital_2V feedback PA L 1 1110001 information C1 VR Quantized 1-bit 2-channel power-level combiner/ FSK polarity transmitter 11- bit 0101110 generator MEMS capacitive Inductor as pressure sensor C/V cyclic ADC Digital B.P. transmitter information antenna

φ CDS C/V converter with automatic offset cancellation 2 φ φ RST 1 CII φ MEMS capacitive pressure sensor 2 C CH I VCM +– +– φ RST CFB Cs V ICMFB OCMFB OCMFB To ADC φ B V 1 C S FB –+ –+ V φ 128C 4C 2C 1C C C CM 2 I H φ D7 D2 D1 D0 2 CII φ φ RST 1 φ 8 bit counter 2 CalEn Digital controlled 2.5-Gain stage reference capacitors Range detector

Figure 3. Electrical system design architecture.

tor, CS, and the reference capacitor, CR. As a transconductance requirement at a reduced cur- common-mode signal, this noise is highly sup- rent dissipation with a resulting slow circuit pressed. The second contributor is the noise speed. The reduced circuit speed, however, is associated with the switches connected between suitable for typical biomedical applications with the pre-amplifier input and output. This noise is signal bandwidth typically ranging from a few eliminated by the CDS scheme as part of the Hertz to a few kilohertz. pre-amplifier 1/f noise and DC offset. Therefore, An ICMFB circuit is incorporated with the the dominant noise source is the third contribu- pre-amplifier design to minimize the input com- tor, the amplifier thermal noise. A fully differen- mon-mode shift caused by the stimulation clock, tial telescopic architecture with p-type MOS hence minimizing offset due to any mismatch of (PMOS) input transistors is chosen as the main parasitic capacitances and potential output drift amplifier for its low noise and low power dissipa- over time. To maintain the same input common- tion compared to other architectures, such as a mode voltage level with the stimulation voltage folded-cascode amplifier architecture. The fold- of VS, a common-mode charge of VS(CS + CR) ed-cascode architecture requires additional bias- must be compensated for by the ICMFB circuit. ing transistors, thus resulting in higher current A CFB of 5 pF is selected to sufficiently compen- dissipation and noise contribution. Compared to sate for the pre-amplifier input common-mode a fully differential telescopic architecture, the shift with a maximum sensor capacitance, CS, up folded-cascode topology improves input com- to 5 pF. The bandwidth of the ICMFB is mon-mode range. However, in the proposed C/V designed to be approximately 80 kHz by using a converter, input common-mode feedback bias current of 1.2 +A. 80 kHz, which is 10 times (ICMFB) is employed to set the pre-amplifier higher than the pre-amplifier closed-loop band- input to a fixed voltage level, thus rendering the width, is chosen to effectively compensate for advantage associated with the folded-cascode the pre-amplifier input common-mode variation. architecture. The amplifier is biased in weak inversion with a 6 +A bias current, achieving an CYCLIC ADC —— input-referred noise of 23 nV/3Hz, which corre- There are six commonly used ADC architec- sponds to a capacitance sensing resolution of tures: flash ADC, integrating ADC, successive approximately 75 aF or a pressure resolution of approximation (SAR) ADC, pipeline ADC, 0.1 mmHg over 1 kHz. With a typical cuff scaling sigma-delta ADC, and cyclic ADC. The follow- factor of 10 percent, a vessel blood pressure sensing outlines the advantages as well as disadvan- ing resolution of 1 mmHg is expected. The weak- tages of each architecture. Flash ADC is for inversion design technique is used to achieve the ultra-high-speed application with a typical reso-

IEEE Communications Magazine • April 2010 101

ond up to 100 Msamples/s, with resolutions from 10 8 to 16 bits. This ADC could be used for imple- b1 Vref/4 menting the proposed microsystem; however, the Range 01 area would be large due to the multiple stages detector required with this architecture. Cyclic (algorith- b0 -Vref/4 00 mic) ADC is well known to achieve low power consumption and high resolution in a small sili- φ 3 con area [3, 5], which is suitable for the intended application. This type of converter can be φ 2 designed without calling for well matched capac- S/H φ C4 itors. The detailed schematic of an 11- bit cyclic 1 ADC is illustrated in Fig. 4. The multiplying dig- V –+ in+ ital-to-analog converter (MDAC) input voltage is sampled twice, followed by an exchange of sampling capacitor and integrating capacitor for V + – a gain of two. Class A/AB amplifiers are used in in- φ 1 the ADC for low power consumption. The over- C4 φ all ADC consumes a current of 6.3 +A, achiev- 2 ing a signal-to-noise-and-distortion ratio φ φ 3 (SNDR) of 65 dB, which is equivalent to an φ φ 8 9 9 effective number of bits (ENOB) of 10.5. φ φ 4 10 V OSCILLATOR-BASED TRANSMITTER φ φ C3 φ Ref 6 5 11 A wireless data telemetry system is a crucial build- φ VCM φ 12 ing block in an implant microsystem to minimize 6 C 2 C1 φ 0 risk of infections and signal interference associat- VCM 4d –+ ed with hard-wire connections. Passive or active Vout+ data telemetry could be used for any implantable φ mircrosystem. Passive data telemetry utilizes 7 Vout- reflected impedance from a secondary circuit load – + φ seen by a primary circuit for data communication. VCM 4d C 0 By utilizing backscatter modulation to provide a φ C2 1 φ 6 12 reflected impedance change at an external coil cir- V MDAC φ φ φ CM cuitry, technically, it consumes zero power. Howev- 6 5 11 C3 V φ φ Ref er, due to the small internal coil connected to the 4 10 microsystem, the coupling coefficient is much φ lower than 0.1 percent. In addition, animal move- 8 ment and title angle result in much weaker coupling with a large variation range. Therefore, this Figure 4. Schematic of an 11-bit cyclic ADC. requires a complex demodulator circuit with high resolution and sensitivity, which is not practical for the current system. An alternative choice, active lution up to 8 bits. The ADC exhibits high power data telemetry, is chosen for the system, and pro- consumption and large size, mainly due to 2N – 1 vides a reliable wireless data link independent of comparators required for an N-bit resolution. animal position and title angle. The challenge of On the contrary, integrating ADC is typically transmitter design for implantable devices is the used for monitoring DC and low-frequency sig- stringent power consumption requirement. nals with high resolution. However, a slow con- FSK modulation is chosen for a reliable wire- version rate is the drawback for this type of less data link and system simplicity compared to ADC, thus making it inadequate for the pro- amplitude shift keying (ASK) and binary phase posed application. SAR ADC is intended for shift keying (BPSK) counterparts. A carrier fre- medium to high resolution (8- to 16-bit resolu- quency of 433 MHz, which is in the industrial, sci- tion) with medium speed, which is suitable for entific, and medical (ISM) radio band, is chosen the proposed biomedical application. However, for the prototype microsystem testing and charac- this ADC is based on a successive approximation terization due to the availability of commercial scheme, thus requiring a precisely matched receivers in this band. In addition, 433 MHz is capacitor array. It is difficult to achieve 11–12- adequate for the implant application, low enough bit accuracy without an extensive layout effort. to avoid increased transmission loss through live In addition, a large capacitor array leads to a tissues and high enough for a small coil antenna large silicon area. Sigma-delta ADC is process- to be employed for overall system miniaturiza- insensitive to the first order and is efficient in tion. An inductor and capacitor (LC)-tuned oscil- terms of power consumption as well as silicon lator with cross-coupled configuration is used for area, but cannot readily be used to process mul- its design simplicity and power efficiency; a tiplexed input signals due to the lack of direct schematic is presented in Fig. 5. This configura- correspondence between an analog input sample tion also allows a single inductor to be employed and digital output bits without employing a deci- for the oscillator. The inductor is implemented by mation filter on-chip. Pipeline ADC is intended a high-Q off-chip inductor with a size of 1.8 × for medium- to high-speed applications. It has 1.24 × 1.24 mm3 to ensure low power consump- become the most popular ADC architecture for tion with an optimal DC bias current of 120 +A sampling rates from a few megasamples per sec- to develop a steady state differential oscillation

102 IEEE Communications Magazine • April 2010

Class-E power amplifier. The measured digital 2 V blood pressure information was transmitted to a It is expected that nearby external commercial receiver by an on- chip oscillator-based transmitter through FSK the proposed M3 M4 modulation in the setup shown in Fig. 6a. The sensing technique –3 worst case bit error rate (BER) is 10 , which is with microsystem limited by the commercial receiver used for test- V+ V- ing. The maximum transmission distance between engineering design the microsystem and the receiver is approximate- will be desirable for ly 15 cm, which is adequate for this application. future human-based MC C MC The measured blood pressure waveforms by the wireless batteryless microsystem and the refer- health monitoring. ence catheter-tip transducer are presented in Other sensing VTX Figs. 6b and 6c, respectively. The two waveforms are well matched in shape, exhibiting similar channels, such as M1 M2 blood pressure characteristics with a calculated temperature, EKG, correlation coefficient of 95 percent. A scaling factor of 0.15 can be calculated from the mea- activity, can be sured waveform. The parameter can be used to readily integrated in μ reconstruct the blood pressure waveform in the V 120 A the system. bias vessel from the recorded waveform from the monitoring cuff. A heart rate of approximately 220 beats/min can also be extracted from both waveforms. A reliable blood pressure waveform Figure 5. Oscillator-based transmitter for data can also be monitored under wireless and bat- telemetry. teryless conditions when the rat is freely running in its own cage after recovery from the surgery. The data measured for 24 hours after implant amplitude of 0.6 V. The inductor also serves the exhibits a noise level increased by approximately 3 function of an antenna for wireless data transmis- dB. The VCO-based transmitter center frequency sion. PMOS capacitors, MC, are used as variable was also decreased from 430 to 426 MHz over 24 capacitors, which are controlled by VTx, present- hours. Further investigations show that the ing Manchester-encoded digital data. The size of enhanced noise was likely caused by vapor pene- the PMOS is designed so that 250 kHz frequency tration through the silicone coating to the electrical separation is realized with a VTx amplitude of 2.5 connections of the MEMS sensor and integrated V, which is adequate for a data rate of 48 kb/s in circuit (IC) chip. The frequency drift was also like- the prototype microsystem. The remaining band- ly caused by vapor penetration to the electrical width can be used for other sensing channels, connection traces, which is equivalent to adding a which can potentially be integrated with the blood 30 fF capacitor to LC tank. The results tell us the pressure sensing microsystem. biological environment is typically the limiting factor for a high-performance implantable system. An improved packaging technique is expected to WIRELESS BATTERYLESS ensure the system performance over time. MICROSYSTEM IN VIVO CHARACTERIZATION CONCLUSION AND FUTURE WORK A wireless and batteryless implantable blood The integrated electronic system has been fabri- pressure sensing microsystem is demonstrated cated in a 1.5 mm CMOS process, exhibiting a for real-time blood pressure monitoring. The chip area of 2.2 × 2.2 mm2, and the fabricated design and trade-offs of the integrated electronic overall microsystem exhibits a weight of approxi- system have been presented in detail. The proto- mately 430 mg including the metal isolation ring, type microsystem was successfully implanted in which was approximately 100 mg [2]. The weight laboratory rats to measure real-time blood pres- of 430 mg was less than 0.2 percent of a typical sure waveforms achieving a resolution of 0.1 laboratory rat body weight with a value between mmHg over 1 kHz with a dynamic range of 60 200 g and 400 g. The total system noise under dB. The demonstrated wireless implantable tech- truly wireless and batteryless conditions is mea- nology will become an important research tool sured to be 750 +VRMS referred to the ADC for system biology research. input, closely matching the designed value, which It is expected that the proposed sensing tech- is equivalent to a resolution of 75 aF or 0.1 nique with microsystem engineering design will mmHg over 1 kHz with a dynamic range of 60 be desirable for future human-based health dB. The total power consumption is 300 +W. The monitoring. Other sensing channels, such as microsystem was implanted in a laboratory rat at temperature, EKG, and activity, can readily be the right carotid artery. A commercial catheter- integrated in the system to achieve a multichan- tip transducer was inserted into the left carotid nel monitoring unit, which is an ongoing project artery as a reference for comparison with an in our research group. Two blood pressure sens- implant, shown in Fig. 6a. During characteriza- ing cuffs can also be positioned with a fixed dis- tion, the microsystem was powered by an external tance along an artery to obtain meaningful coil fabricated on a PCB positioned underneath real-time blood flow information for cardiovas- the rat with a size of 15 cm × 20 cm driven by a cular disease study [6].

IEEE Communications Magazine • April 2010 103

Receiving antenna Class-E amplifier Right carotid artery driving external coil

Microsystem for blood pressure monitoring

Laboratory rat Catheter-tip transducer

External coil (15 cm × 25 cm)

(a) 800 160 790 780 150 770 140 760 6.2 mmHg 750 38 mmHg

Output code 130

740 Pressure (mmHg) 120 730 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Time (s) Time (s) 790 160 780 770 150 760 140

Output code 750 6.2 mmHg 130 38 mmHg

740 Pressure (mmHg) 730 120 0.10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (s) Time (s) (b) (c)

Figure 6. Wireless batteryless blood pressure monitoring microsystem laboratory rat evaluation: a) microsystem implant; b) measurement from the blood pressure microsystem; c) measurement from the catheter-tip transducer.

REFERENCES (CWRU)in 2009. His research focuses on MEMS sensors, mixed-signal IC design, and microsystem integration for [1] B. Hoit et al., “Naturally Occurring Variation in Cardio- biomedical and harsh environmental applications. He is a vascular Traits among Inbred Mouse Strains,” senior IC design engineer for Medtronic Inc. Minneapolis, Genomics, vol. 79, no. 5, May 2002, pp. 679–85. Minnesota, working on next-generation implantable medi- [2] P. Cong, W. H. Ko, and D. J. Young, “Wireless cal devices. Implantable Blood Pressure Sensing Microsystem Design for Small Laboratory Animals Monitoring,” Sen- WEN H. KO [F] received Ph.D. degrees in electrical engineer- sors Materials, vol. 20, no. 7, 2008, pp. 327–40. ing from Case Institute of Technology, Cleveland, Ohio, in [3] P. Cong, W. H. Ko, and D. J. Young, “Low Noise mWatt 1956 and 1959 respectively. He has been an assistant, Interface Circuits for Wireless Implantable Real-Time associate, and full professor of electrical engineering and Digital Blood Pressure Monitoring,” CICC ’08, San Jose, biomedical engineering, at CWRU since 1959, 1962, and CA, Sept. 2008, pp. 523–26. 1967, respectively. He became a Professor Emeritus in elec- [4] C. C. Enz and G. C. Temes, “Circuit Techniques for trical engineering of CWRU in July 1993 and is active in Reducing the Effects of Op-Amp Imperfections: Autoze- research on MEMS and biomedical implants including roing, Correlated Double Sampling, and Chopper Stabi- micropackage and thin film power supplies. He is a fellow lization,” Proc. IEEE, vol. 84, no. 11, Nov. 1996, pp. of the American Institute of Medical and Biological Engi- 1584–1614. neering. [5] P. Li et al., “A Ratio-Independent Algorithmic Analog- to-Digital Conversion Technique,” IEEE J. Solid-State Cir- DARRIN J. YOUNG received his B.S., M.S., and Ph.D. degrees cuits, vol. 19, no. 6, Dec. 1984, pp. 828–36. from the Department of Electrical Engineering and Com- [6] K. Takahata et al., “A Wireless Microsensor for Monitor- puter Sciences at the University of California at Berkeley in ing Flow and Pressure in a Blood Vessel Utilizing a 1991, 1993, and 1999, respectively. He joined the Depart- Dual-inductor Antenna Stent and Two Pressure Sen- ment of Electrical Engineering and Computer Science at sors,” 17th IEEE Int’l. Conf. MEMS, 2004, pp. 216–19. CWRU in 1999 as an assistant professor. In 2009 he joined the Electrical and Computer Engineering Department at the University of Utah as a USTAR associate professor. His BIOGRAPHIES research interests include MEMS design, fabrication, and integrated analog circuits design for wireless sensing, PENG CONG ([email protected])______received his Ph.D. biomedical implant, communication, and general industrial degree from the Department of Electrical Engineering and applications. Computer Science at Case Western Reserve University

104 IEEE Communications Magazine • April 2010

CALL FOR PAPERS SYNCHRONIZATION OVER ETHERNETAND IP IN NEXT-GENERATION NETWORKS Network synchronization plays a central role in digital telecommunications. It determines the quality of most services provided by the network operator. Traditionally, synchronization has been distributed across telecommunications networks using the TDM links for which the networks were designed (i.e. E1 and DS1 circuits). Several fixed and mobile Operators are migrating to a next-generation network (NGN) with IP packet-switched network infrastructure. Ethernet transport is becoming increasingly commonplace. This trend is driven by prospected lower oper- ative costs and by the convergence between fixed and mobile services. However, migrating trunk lines to IP transport poses significant technical challenges, especially for circuit emulation and synchronization of network elements. The evolution of communications networks towards packet-switching has increased interest in the distribution of synchronization using packet methods. This has a twofold impact: 1. Synchronization distribution over packet networks using packet-based methods has become a focus of activity in thestandards bodies (ITU-T G.8261/2/3 and IEEE 1588); 2. The traditional model, in which synchronization distribution is engineered carefully for optimal performance, may give way to scenarios in which there is a greater expectation of ad-hoc synchronization quality achieved without as much need for provisioning as has traditionally been the case — similar to Ethernet "plug and play". The latter point widens the scope of interest in synchronization beyond specialists to the wider audience of telecommunications engineers. A striking example is the distribution of synchronization to next-generation wireless base-stations, which are connected to the core network only via packetswitched networks, but still require highly accurate synchronization to meet service quality expectations.

SCOPEOF CONTRIBUTIONS Authors from industry and academia are invited to submit papers for this special issue of IEEE Communications Magazine on next generation synchronization, including synchronization distribution over Ethernet and IP networks. The scope of the issue includes, but is not limited to the following topics of interest: • Key emerging standards in the area of synchronization over packet networks • Timing scenarios in various network applications • Tutorial papers describing packet network characteristics which impact synchronization transport • Implementation challenges in achieving high-quality synchronization using the new technologies • Carrier and vendor experience in deployment • Measurement techniques for characterizing and qualifying packet-based synchronization The special issue is expected to have 5-7 papers.

SUBMISSION GUIDELINES Articles should be tutorial in nature, with the intended audience being all members of the communications technology communities. They should be written in a style comprehensible to readers outside the specialty of the article. Mathematical equations should not be used (in justified cases up to three simple equations are allowed). Articles should not exceed 4500 words. Figures and tables should be limited to a combined total of six. The number of references is recommended to not exceed 10 (maximum 15). Complete guidelines for preparation of the manuscript are posted at http://dl.comsoc.org/livepubs/ci1/info/sub_guidelines.html. Please send a PDF (preferred) or MSWORD formatted paper via Manuscript Central (http://mc.manuscriptcentral.com:80/commag-ieee). Register or log in, and go to the Author Center. Follow the instructions there. Select "February 2011/Synchronization over Ethernet and IP in Next-Generation Networks". Manuscript Deadline: May 31, 2010 Notification of acceptance: September 30, 2010 Final paper submission: November 30, 2010 Publication date: February 2011

GUEST EDITORS Stefano Bregni Ravi Subrahmanyan Politecnico di Milano, Dept. of Electronics and Information National Semiconductor Corp. Piazza Leonardo da Vinci 32, 20133 Milano MI, Italy One Stiles Road, Suite 305, Salem, NH, 03079, USA

Email: [email protected]: [email protected]

ACCEPTED FROM OPEN CALL Power Line Communication Networks for Large-Scale Control and Automation Systems

Gerd Bumiller, iAd GmbH Lutz Lampe, University of British Columbia Halid Hrasnica, Eurescom GmbH

ABSTRACT ization for high-speed PLC systems within the IEEE [4]. Power line communications uses the existing The single main advantage of PLC over other power line infrastructure for communication wired communication solutions is the existence purposes. While the majority of recent contribu- of a power line infrastructure. This, for example, tions have discussed PLC for high-data-rate allows electricity companies to retrofit their applications like Internet access or multimedia power line networks for communication purpos- communication serving a relatively small number es at little additional cost. In fact, the energy dis- of users, in this article we are concerned with tribution grid is perhaps the most ubiquitous PLC as an enabler for sensing, control, and infrastructure worldwide, and its extremely high automation in large systems comprising tens or penetration opens the door for a plethora of even hundreds of components spread over rela- applications supported by PLC. Alongside the tively wide areas. Typical examples of such sys- aforementioned applications, especially the use tems are energy management (Smart Grid) and of PLC for advanced energy management has facility automation systems. We provide a discus- experienced a strong boost. Examples of this sion of the communication network require- trend include the recently completed research ments common to such systems and present and development project Real-Time Energy transmission concepts for PLC to make use of Management via Powerlines and Internet (REM- the existing infrastructure resources (i.e., power PLI), which involved nine partners from five lines) to meet these requirements. European countries and was funded by the Euro- pean Union (see www.rempli.org), and the Pow- INTRODUCTION erline Intelligent Metering Evolution (PRIME) project launched by the Spanish electric utility Already during World War II, power lines were Iberdrola and joined by industrial partners from considered as a means of data transmission [1]. Europe and the United States, whose aim is the The main usage of power line communications specification of an open and non-proprietary (PLC) has been by electricity companies for PLC-based telecommunications architecture that sending control signals at low rates and in sever- “could meet the future requirements on cus- al home automation products. It was only recent- tomer real time interfacing and smart grid evolu- ly, spurred by the deregulation of the tion” (see www.iberdrola.com/suppliers/ telecommunication and energy market in the ______SmartMetering for a White Paper). More gener- late nineties, that communication over power ally, the ubiquity of power distribution lines ren- lines has received wider attention and is per- ders PLC an excellent candidate for industrial ceived by many as a viable alternative or valu- command-and-control and facility automation able complement to other wired or wireless systems, in which a common communication net- communications systems. work connects a large number of devices that This is particularly true for Internet access are spread over a wide area. We collectively and indoor local area networks (LANs), where refer to such systems as large-scale control and application of so-called broadband PLC is con- automation systems in the following. sidered. Broadband PLC assumes service pro- The design and performance requirements vision for multimedia applications consuming for PLC in large-scale control and automation larger data rates and serving a limited number systems are decidedly different from those for of users, and its new popularity is evidenced PLC in access or indoor systems. Different net- by two special issues on PLC-based LANs and work parameters, such as geographical coverage access networks in this magazine in 2003 [2, or number of network nodes, and different appli- 3], and the recent developments in standard- cation-related features, such as size of data pack-

ets or maximal response time, make it necessary transformer station and to the medium-voltage to apply different transmission concepts. In the layer, the network size can grow to thousands of The energy first part of this article we describe these require- nodes. Fast access to individual meters is also management system ments and derive the necessary features of an needed to enable advanced customer service. enabling PLC network. This is followed by a For example, in a recent tender a Dutch electric of the future description of transmission techniques that have utility required that their call center can access foresees the been developed for such PLC networks in the 90 percent of all meters within five seconds. In past few years [5–9]. We focus on the physical Germany the national regulator Bundesnetza- implantation of and medium access control (MAC) layer tech- gentur considers the possibility of real-time considerable niques, which are closely linked to the use of switching between electric utilities, and the ven- intelligence into the PLC as communication technology. The gist of dors of billing software work on solutions for our discussion is that conceptually fairly simple customers to find the presently least expensive distribution grid single-frequency networking together with flood- provider. Again, fast access to meters is an which essentially ing of messages are attractive methods for large important element for these solutions. PLC networks. While such an approach has been Another Smart Grid functionality is the man- renders it a situation- advocated in wireless ad hoc networks [10], we agement of energy distribution using a supervi- aware network of submit that it is also suitable for PLC networks sory control and data acquisition (SCADA) interconnected (with no mobility) to enable service guarantees. system. SCADA sensors permanently monitor To support this observation, we finally present a the grid load and report to a control center, sensors and quantitative comparison of flooding and routing from which open/close commands are sent to actuators. based on performance parameters specifically switches to adapt the distribution structure to relevant to the considered application scenarios. the dynamics of energy generation and consump- Most of the presented material originates from tion. Such operations become more frequent work conducted for energy management systems, with increasing decentralization of energy gener- under the umbrella of REMPLI, and airfield ation, and they need to be executed reliably and ground lighting automation systems. Therefore, in real time in order to maintain grid stability. even though we keep the ensuing description Thus, SCADA imposes strong reliability and generic for the most part, we repeatedly refer to real-time requirements on PLC. these two specific applications. Airfield Ground Lighting Automation Sys- tems — Modern airfield ground lighting (AGL) CONTROL AND AUTOMATION automation systems enable individual lamp con- YSTEMS SING trol and monitoring of sensors deployed at air- S U PLC fields. Such functionalities are needed to meet We start by considering the two mentioned the latest recommendations by national and application examples for large-scale control and international regulators to enhance safety of air- automation systems to motivate PLC as a very craft ground movement and to aid visual guid- attractive solution and concretely show what is ance systems. Figure 1 illustrates a typical wiring required of a PLC network. topology of an AGL system. Devices such as lamps and microwave sensors are arranged in a APPLICATION EXAMPLES ring structure of typically between 3 and 15 km Energy Management Systems — The energy connected to a constant current supply via trans- management system of the future foresees the formers. implantation of considerable intelligence into PLC is a cost-effective and elegant solution the distribution grid, which essentially renders it to enable communication between the airport a situation-aware network of interconnected sen- tower and the ground lighting system, particular- sors and actuators. These intelligent grids of ly for existing airport infrastructures where tomorrow have gained global attention under build-up of new dedicated communication net- the label Smart Grid [11]. The realization of the works would be expensive. The communication Smart Grid concept entails the existence of a network has to bridge considerable distances and reliable communication network, which likely also connect across power-electric components, integrates several communication carriers. Due especially transformers, which are not designed to the inherent availability of power lines as car- for high-frequency communication signals. In riers and the resulting advantages with respect to terms of signal flow, we note that all data com- installation costs, we expect that PLC will play a munication needs to go through a central node prominent role in the implementation of Smart directly connected to the tower (Fig. 1). Further- Grid. more, the reaction time, the round-trip delay of Let us consider a few typical examples of a signal between the tower and a lamp, is criti- Smart Grid functionalities to illustrate the cal. Since the communication channels are time- requirements for the communication network. variant, the PLC system needs to permanently The first example is real-time pricing to balance monitor the communication quality to all net- energy consumption and moderate peak loads. work nodes to guarantee a certain maximal reac- The key components for real-time pricing are tion time. The time variance of the channels is intelligent energy meters and the possibility of due to different current steps of the regulator, communication with a central data collection variable loads in the circuit, crosstalk from other and control station. Assuming that every house- rings that often run parallel over several kilome- hold is equipped with such a meter, the PLC ters, and even weather conditions. Hence, the network between meters and the common trans- PLC system needs to be sufficiently robust with former station can easily include 300 nodes or respect to channel variations. In addition, a node more. If the PLC network extends beyond the failure must not affect communication to other

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Automation and grid Sensor management systems have mainly Data link Remote Remote Remote Tower a master-slave node (slave) node (slave) node (slave) structure, because these applications are strictly hierarchically Constant PLC current central organized. In facility node regulator (master) management, client-server networks are becoming popular. Remote Remote Remote node (slave) node (slave) node (slave)

Sensor

Figure 1. Illustration of the ring structure of an airfield ground lighting automation system. A typical ring has a length between 3 and 15 km, and includes between 10 and 200 remote nodes (lamps, sensors).

nodes. Hence, redundant signal paths between Robustness to Changes — In PLC networks the central and other network nodes are manda- the communication channel may change abruptly tory for the PLC network. during normal operation. For example, switching operations in medium-voltage energy systems to REQUIREMENTS FOR THE PLC INFRASTRUCTURE balance the power consumption over the distri- The described application examples are repre- bution grid will result in changes of channel sentative in that the PLC network needs to con- transfer functions in sizeable parts of the PLC nect a large number of devices like switches, network. The PLC network design must be able sensors, meters, and lamps that are distributed to cope with such abrupt changes, which means over a relatively wide area. In the following we that the connectivity must be maintained during attempt to categorize the typical requirements or quickly recovered after these changes. Since for the PLC infrastructure in order to support severe network disruptions due to, say, physical large-scale control and automation systems. removal of network links, are often not excep- tional events but occur frequently during normal Network Coverage and Data Flow — Appli- operation, maintenance of system availability is cation protocols for metering, automation, facili- only possible with redundant communication ty or grid management support point to links and autonomous use of redundancies. That multi-point communication with mainly short is, a PLC network that needs to estimate link data packets. Automation and grid management qualities and re-establish connections after systems mainly have a master-slave structure, topology changes have occurred will not be able because these applications are strictly hierarchi- to fulfill reliability requirements. Instead, ad hoc cally organized. In facility management client- networking features are needed. It is important server networks are becoming popular. A client to note that the removal and addition of net- polls the server (data point), or the server push- work nodes, or changes in the impedance of the es the data periodically. In metering applications associated device also affect the communication both strictly hierarchical and client-server struc- channels in a large neighborhood around this tures are used. All applications have in common node. This behavior is very different from wire- that the devices of the system represent the com- less communications, where the mere presence munication nodes of the PLC network, and each or absence of a wireless device does not affect of these nodes needs to be connected to the cen- the link quality for another device. tral node (master, server). This requirement is challenging considering that many network Quality of Service — The main quality of ser- nodes are remote from the central node, and vice (QoS) requirements for the PLC network in perhaps serve time-critical applications like control and automation systems are high com- those mentioned in the previous section. Fur- munication reliability, high overall network thermore, while individual nodes communicate throughput, and strict limits on delay. Often only small amounts of data at a time, the total messages transmitted from nodes to the central data volume to be transferred through the net- node (e.g., notification about a sudden voltage work is substantial. Hence, resource-efficient drop) or from the control center to network transport of data to and from the central node is nodes (e.g., a switching command for an actua- mandatory to achieve sufficient network cover- tor) are time-critical. Failure to meet delay age. requirements can have serious consequences,

108 IEEE Communications Magazine • April 2010

often with human safety at stake. In addition, changes in PLC networks are often abrupt and due to the time variance of the communication affect a large fraction of nodes. The need to The spatial channels, the functionality of all network nodes establish a route would compromise communica- needs to be verified continuously to guarantee tion reliability and delay constraints. Third, con- dimension of the PLC reliable data transfer and system response time. sidering the delivery of a single packet, flooding network renders Since optimization of throughput, reliability, and minimizes the delay in that it always finds the direct communica- delay often pose conflicting demands on the shortest path to the destination. Key for flooding design of the communication protocol, manage- to be effective is the application of the SFN con- tion between the ment of QoS requirements is a nontrivial task. cept. SFN transmission avoids congestion for the central node and all packet that is flooded, and thus accomplishes other network RANSMISSION ONCEPTS FOR efficient use of network redundancy and mini- T C PLC mizes transmission delay. devices infeasible. To We now present transmission concepts apt to On the downside, flooding has the potential still achieve complete meet the need for network coverage, link redun- to create closed communication loops and to dancies, and guaranteed QoS outlined above. massively occupy channel resources. Further- coverage, messages more, different packets flooded simultaneously need to be repeated, SINGLE-FREQUENCY NETWORK CONCEPT in a specific geographical area can destroy each The spatial dimension of the PLC network ren- other. To avoid or mitigate these effects, two which is also known ders direct communication between the central measures are suggested. First, active network as multihop trans- node and all other network devices infeasible. nodes (repeaters) monitor the packets or packet mission or relaying. To still achieve complete coverage, messages numbers and ensure that every packet is repeat- need to be repeated, which is also known as ed only once. Second, each packet is equipped multihop transmission or relaying. Considering with a counter nrepeat that specifies the maximal that PLC reuses an existing infrastructure and number of times a packet can be repeated before the broadcast nature of the PLC channel, an it reaches the destination, and this counter is altruistic repeater concept is appealing. That is, decremented during each repetition. We note network nodes that overhear a message for that two different counters may be used for another destination are prepared to retransmit transmission in opposite directions due to poten- this message. Such a repeater concept makes tially non-reciprocal transfer functions or differ- optimal use of the available communication ent interference situations at different locations. nodes in the network, and is flexible enough to also ensure network coverage and communica- MIXED DETERMINISTIC AND tion reliability under changing channel condi- RANDOM MAC CONCEPT tions and topologies. In particular, the use of multiple repeaters to relay the same message sig- As discussed earlier, a feature common to many nal provides redundant signal paths, which are applications is that traffic flows to and from a needed to minimize network outages. To man- central node, which suggests a centralized MAC age this multirelay transmission with minimum with a master-slave concept. The organization of use of communication resources, the single-fre- the transmission in the downlink direction (from quency network (SFN) concept, which is known master to slaves) is simple since only the master from macrodiversity wireless communication sys- transmits data to one or multiple slaves. tems [12], can be applied. The SFN allows all The situation is different for the uplink, repeaters to transmit simultaneously using the where a number of slaves may have data to be same frequency band. The next receiving node(s) transmitted to the master at the same time. A sees a linear superposition of the retransmitted first option would be a purely deterministic signals, which is indistinguishable from a single MAC protocol that completely eliminates signal signal being sent over an equivalent multipath collisions. To this end, slaves could be succes- channel. Hence, any communication technique sively polled by the master to see whether uplink suitable for transmission over multipath channels resources are required. To ensure a certain can be applied in an SFN. One popular method polling rate, which defines the reaction time of is orthogonal frequency-division multiplexing the PLC network, a certain fraction of channel (OFDM) [5, 12]. We note that SFN-PLC trans- use has to be reserved for this mechanism. For mission benefits from signal enhancement due to example, consider a sensor which monitors rare concurrent retransmission. In some cases events that occur on average, say, once every destructive interference may occur, which can be day, but which require a fast response time of, mitigated using distributed space-time coding say, 10 s. The master would have to poll the sen- concepts presented in [8]. sor every 10 s, which is an excessive waste of resources. Furthermore, while this approach may FLOODING CONCEPT be feasible in relatively small networks, the reac- If altruistic relaying is used to route a message tion time can quickly become unacceptably large through the network, the flooding concept is for networks with hundreds of nodes. For the implemented. We submit that flooding is an same reasons, other deterministic medium access attractive packet delivery process in control and policies, such as master-slave-oriented bus proto- automation PLC networks for the following rea- cols, token ring protocols, or solutions with fixed sons. First, flooding eliminates almost all routing time slots reserved for each individual network overhead, which can be substantial for large net- node within a time-division multiple access works with multiple repeater levels. Second, it is (TDMA) scheme are also not well suited. Ran- extremely robust to network changes. This is dom medium access techniques, such as Aloha crucial for applications such as energy manage- or carrier sense medium access (CSMA), offer ment or AGL systems. As mentioned above, more flexibility in this regard. Since reliable car-

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Figure 2. Tree topology as an example model for an energy distribution grid with 100 (left) and 200 (right) nodes (shown as circles). The x- and y-axes are the main supply lines to which all nodes are connected. The master is located at the origin, and the slave nodes are generated according to a uniform distribution over the diamond-shaped area defined by the maximum cable length between master and slaves, where cables run in parallel to the x- and y-axes. The node density is kept constant regardless of the number of nodes.

rier sensing in PLC is complicated by the hidden anisms due to SFN-based flooding work in node problem [13], particular collision avoidance favor of random access with slotted Aloha. techniques have to be employed like those devel- First, as long as at least one repeater node oped for indoor PLC systems [14]. However, receives a signal originating from another node application of mechanisms for solving the hidden successfully, the underlying message is not node problem and collision avoidance add con- annihilated even though signal collisions may siderable overhead for transmission with small have occurred. Second, SFN transmission can data packets and therefore are not well suited be exploited to reduce the waiting time between for automation and control PLC systems. In case retransmission attempts and thus improve over- of purely random access without collision avoid- all transmission delay applying the concept of ance (i.e., Aloha or slotted Aloha), the packet local acknowledgments devised in [7]. delay can become unacceptably large, and network throughput is limited in the case of highly REMARKS loaded networks with a large number of nodes. We would like to remark on some of the chal- These considerations motivate a hybrid lenges associated with the described SFN-based MAC protocol that combines elements of deter- flooding concept. ministic and random medium access. First, the master establishes a network-wide TDMA Synchronization — SFN-based flooding frame structure through the broadcast of con- requires a network-wide clock. This can be estab- trol packets to all nodes. Within each frame the lished through the TDMA structure, which is master allocates time slots for dedicated mas- maintained by broadcast packets sent by the ter-slave connections serving services such as master. Every packet is equipped with a synchro- polling. Then the remaining time slots are used nization preamble [9] based on which a slave for random medium access in the uplink, which adjusts its timing. Since broadcast packets serve allows slaves to connect spontaneously with the several purposes, they are sent regularly. Experi- master (e.g., if an event that deserves quick ments have shown that timing synchronization reaction from the master is detected or a slave with an accuracy of very few (often fewer than joins the network). For the sensor example two) symbol intervals is easily achieved, which mentioned above, the master would poll the also means that only very little additional guard sensor at regular intervals much larger than the space between transmissions is required for an response time to ensure that the sensor is func- SFN. We note that frequency synchronization is tional and synchronized to the TDMA frame not problematic due to the low carrier frequen- structure. When the sensor has an event to cies used in narrowband PLC. report, it uses random access within the dedicated uplink frame to send the message. Con- Channel Estimation and Error Propagation sidering that per-node link utilization is not — The need for receiver-side channel estimation high, slotted Aloha or one of its variants is the in SFN-based flooding can be bypassed using method of choice for the random access within differential modulation (e.g., across subcarriers the TDMA frame structure. Since all network if OFDM is applied). Likewise, the effect of resource control rests with the master, it dimen- error propagation can be neglected assuming the sions the frame structure in accordance with use of error detection, such that only nodes the QoS demands from the specific applications which deem a packet as received correctly will served by the network. Furthermore, two mech- retransmit it.

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Channel Occupation and Energy — Clearly, there is a price to be paid for not needing a Ring topology Tree topology route. First, redundant retransmissions occupy Channel model channels unnecessarily and prevent other mes- 10 nodes 100 nodes 100 nodes 200 nodes sages being sent. When one TDMA frame trav- — els, no other frame can travel in a certain D rout,opt 30 427 421 1027 geographical area, which means that spatial reuse and therefore packet origination rates are — D flood,opt (ES) 29 419 387 993 limited. Second, the use of many retransmissions — 28 403 367 939 wastes energy, which undermines the purpose of D flood,opt (EC) smart grids. These problems are mitigated — through flooding using counters as described D flood,adapt (ES) 30 423 393 1003 — above. Variations of flooding that aim at reduc- D (EC) 29 404 368 945 ing the number of redundant broadcasts [15] can flood,adapt further remedy the situation. Since the location Table 1. Comparison of the average duration of a polling cycle using optimal of many network devices is static, topology infor- routing and flooding with optimal and adapted number of retransmissions mation may be used during flooding. For exam- nrepeat. Duration is measured in number of time slots. EC refers to the case ple, in parts of the network with high when the energies of the multiple signal paths are aggregated at the receiver; in connectivity, only a subset of nodes relays a mes- ES only the individual channel with the largest energy is considered. sage. Furthermore, signal waves can be directed toward the destination, which also increases multiplexing capability. However, topology information needs to be exploited with care as, for domly generated tree topology with 100 and 200 example, in ring topologies found in medium- nodes, respectively. The latter are illustrated in voltage energy distribution grids or AGLs (Fig. Fig. 2. For SFN-based flooding we distinguish 1), a single node failure can completely change two scenarios for superposition of simultaneous- the direction in which the signal wave needs to ly relayed signals: aggregation of signal energies propagate to reach the destination. from all signal paths (denoted energy combining [EC] in Table 1) and selection of the individual channel with the largest energy (denoted energy NUMERICAL RESULTS: selection [ES]). LOODING VS OUTING The figures in Table 1 are the average dura- F . R tion of a polling cycle measured in number of To make the argument for SFN-based flooding time slots. We observe that flooding consistently more concrete, in this section we provide numer- achieves a lower polling cycle duration than ical performance results for three specific crite- routing. This is due to the fact that with flooding ria pertinent to large-scale PLC networks. We the packet is received via the optimal route and compare flooding with the alternative of central- via additional repeater paths, and thus the prob- ized proactive routing, for which every message ability of successful transmission is increased is only retransmitted by exactly one repeater compared to routing. Furthermore, the restric- node at every repetition level, and the route is tion of the number of repetitions in flooding due determined at the master node based on link to nrepeat avoids unnecessary occupation of chan- quality information given by the packet error nel resources. We further observe that perfor- rate (PER). mance degradations due to in situ adaptation of nrepeat are less than 4 percent. AVERAGE DURATION OF A POLLING CYCLE Polling is often one of the fundamental network DURATION OF A BROADCAST TRANSMISSION operations. For example, in AGL automation it In the considered PLC networks messages are is critical to continuously monitor the functional- frequently broadcast from the master to all ity of all devices; thus, the master frequently slaves. The purpose of broadcast messages is polls all slaves. manifold. It serves, for example, to update the — The average duration of the polling cycle D is TDMA frame structure, to inform slaves of defined as the average time the master needs to which slots are used for specific services and complete a single packet-request-response ser- physical-layer parameters, to download software vice with every slave. An analytical expression updates, or to transmit fast time-varying applica- — for a lower bound for D for the case of routing tion-specific parameters such as the distance of systems can be obtained by making the idealized an approaching airplane in AGL automation sys- assumption that the instantaneous PERs for all tems. node-to-node links are available at the master. Flooding is a natural fit for fast broadcast — To obtain an analytical expression for D for the transmission as it utilizes the very broadcasting flooding-based system, we assume that the maxi- nature of the PLC channel. The duration of a mal number of packet retransmissions, n , is broadcast is simply max{n } times the dura- — repeat repeat chosen such that D is minimized. Furthermore, tion for a downlink slot. In case of routing, we we have simulated SFN-based flooding using an assume that the master sends the broadcast mes- adaptation method for n . sage to a number of slaves selected such that the repeat — Table 1 shows the numerical results for D union of all nodes that receive the message — assuming optimal routes, D assum- transmitted along those routes forms the com- rout,opt — flood,opt ing optimal nrepeat, and Dflood,adapt with adapted plete set of nodes. In this way, the address field nrepeat for a ring topology (Fig. 1) with 10 and of the broadcast packet is not expanded com- 100 uniformly distributed nodes, and for a ran- pared to a unicast packet. To minimize the dura-

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To illustrate the agility of flooding, we simu- Ring topology Tree topology lated polling cycles for 100 nodes that first were Channel model arranged in a ring structure and after a certain 10 nodes 100 nodes 100 nodes 200 nodes number of cycles were rearranged into a random-tree structure. We hasten to say that such Routing 5 8 37 73 a dramatic topology change is unrealistic and only serves as an extreme academic example to Flooding 3 4 5 5 test the robustness of flooding. In the simulations a request to a slave was repeated until the Table 2. Comparison of the average duration for a broadcast to all slaves using master successfully received a response. Figure routing and flooding. Duration is measured in number of time slots. 3 shows the measured duration for a polling cycle, where the network topology is changed before cycle number 1. We observe that before the topology change, the duration of the polling 800 ES case cycle jitters around average values of about 410 EC case (EC case) and 425 (ES case) time slots. The 750 length of the polling cycle jumps to about 700 (EC) and 780 (ES) slots right after the network 700 change, but it is already reduced again by about 250 slots in the following cycle. Already after 5 650 to 7 polling cycles, the cycle durations have converged to the (new) stationary values. To have 600 an estimate for the length of the adaptation process in absolute time, we assume a slot dura- 550 tion of 10 ms. This value is typical for PLC transmission in the CENELEC-A band with a 500 bandwidth of 50 kHz. Then the average duration of a polling cycle for 99 slaves would be 450 between 4 and 4.5 s according to the results in 400 Fig. 3. The first polling cycle after the abrupt

Duration of polling cycle (number of slots) topology change would require 7 to 8 s to suc- 350 cessfully reach all slaves, but within only 30 to 40 s the adaptation to the new topology is com- -15 -10 -5 0 5 10 15 20 25 30 pleted. This very fast adaptation, which is only Polling cycle (0 = switch of channel mode) possible with an algorithm with short memory, satisfies real-time requirements for the commu- Figure 3. Duration of polling cycles for flooding before and after an abrupt nication system in, say, Smart Grid applications topology change. even during and after a switching instant. Hence, SFN-based flooding is a very attractive solution in this regard as well. tion of the broadcast, we apply a greedy algorithm that selects the next slave such that a max- ONCLUSIONS imal number of nodes is reached along its route. C Table 2 shows the time needed to deliver a In this article we have presented an overview of broadcast message with routing and flooding for the requirements for PLC to become an enabler the same four network topologies considered for for advanced control and automation systems polling. The time is measured in number of time such as energy management and facility automa- slots, and the particular figures were determined tion systems. Starting from these requirements such that the PER for all slaves is less than 0.1 we have described suitable PLC transmission percent. It is interesting to observe that perfor- concepts. We have advocated, and in part sub- mance differences between flooding and routing stantiated with numerical evidence, that the are moderate for ring structures, whereas they combination of single-frequency networking become significant for tree topologies. In partic- with flooding embedded into a hybrid MAC ular, flooding is rather insensitive to the underly- protocol is attractive to meet the application ing topology since signal waves propagate in all requirements. The efficacy of the presented directions. Likewise, the actual number of nodes concepts has been verified in field trials under is insignificant as long as the spatial extension of the umbrella of the REMPLI project, and PLC the network does not change significantly. products based on this technology are currently being used in a number of pilot projects for ROBUSTNESS TO TOPOLOGY AND advanced meter management (e.g., in Karczew, CHANNEL FLUCTUATIONS Poland) and streetlight control (e.g., in Fürth, Germany). We close by noting that the future We have already pointed out earlier that the proliferation of PLC as an enabler for Smart quality of communication links in a PLC net- Grid functionalities is not only a technological work can vary with time due to, say, load issue, but also depends strongly on how swiftly changes. Switching operations even change the electric utilities are able to implement necessary network topology. A typical example of a severe changes in the energy distribution process, and topology change would be the opening of a ongoing legislative developments concerning medium-voltage distribution line ring structure infrastructure reliability and new services like at a location close to the master node. real-time pricing.

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REFERENCES BIOGRAPHIES

[1] H. Ferreira et al., “Power Line Communication,” in Ency- GERD BUMILLER [M] ([email protected])______received his The efficacy of the clopedia of Electrical and Electronics Engineering, J. Diplom (Univ.) and Ph.D. degrees in electrical engineering presented concepts Webster, Ed., Wiley, 1999, pp. 706–16. from the University of Erlangen, Germany, in 1997 and [2] H. A. Latchman and L. W. Yonge, “Power Line Local 2009, respectively. He joined iAd GmbH, Germany, as a has been verified in Area Networking,” IEEE Commun. Mag., vol. 31, no. 4, communication system developer in 1997. Since 2000 he Apr. 2003. has been chief developer responsible for all power line field trials under the [3] S. Galli, A. Scaglione, and K. Dostert, “Broadband Is communication projects of iAd. In this role he has been Power: Internet Access through the Power Line Net- involved in a number of European and international pro- umbrella of the work,” IEEE Commun. Mag., vol. 31, no. 5, May 2003. jects on high-data-rate access, control and automation, REMPLI project, and [4] S. Galli and O. Logvinov, “Recent Developments in the and Smart Grid power line communications. He has pub- Standardization of Power Line Communications within lished widely in the area of power line communications PLC products based the IEEE,” IEEE Commun. Mag., vol. 46, no. 7, July with contributions to channel measurement and modeling, 2008, pp. 64–71. coupling, synchronization, multicarrier modulation, coding, on this technology [5] G. Bumiller, “Single Frequency Network Technology for routing, and ad hoc networking. He is a member of Work Medium Access and Network Management,” IEEE Group 2 (Network Operations) of the EU Smart Grids initia- are currently being ISPLC, Athens, Greece, Mar. 2002. tive (www.smartgrids.eu), participates in the Open Meter- used in a number of [6] G. Bumiller, “Power-Line Physical Layer Emulator for ing initiative of ZVEI and FIGAWA in Germany, and is a Protocol Development,” IEEE ISPLC, Zaragossa, Spain, member of AK 461.0.141 and UK 716.1 in the German pilot projects for Mar. 2004. standardization body DKE. [7] L. Do, H. Hrasnica, and G. Bumiller, “SALA MAC Proto- advanced meter col for PLC Networks Based on Single Frequency Net- LUTZ LAMPE [SM] ([email protected])______received his Diplom work Technique,” IEEE ISPLC, Orlando, FL, Mar. 2006. (Univ.) and Ph.D. degrees in electrical engineering from the management. [8] L. Lampe, R. Schober, and S. Yiu, “Distributed Space- University of Erlangen, Germany, in 1998 and 2002, Time Block Coding for Multihop Transmission in Power respectively. Since 2003 he has been with the Department Line Communication Networks,” IEEE JSAC, vol. 24, July of Electrical and Computer Engineering at the University of 2006, pp. 1389–1400. British Columbia, where he is currently an associate profes- [9] G. Bumiller and L. Lampe, “Fast Burst Synchronization sor. His research interests are in communication theory for Power Line Communication Systems,” EURASIP J. with applications to wireless and power line communica- Adv. Signal Process., vol. 2007, article ID: 12145. tions. He is Vice-Chair of the IEEE Communications Society [10] A. Scaglione and Y.-W. Hong, “Opportunistic Large Technical Committee on Power Line Communications. He Arrays: Cooperative Transmission in Wireless Multihop was General Chair of the 2005 International Symposium on Ad hoc Networks to Reach Far Distances,” IEEE Trans. Power Line Communications and the 2009 IEEE Interna- Signal Process., vol. 51, no. 8, Aug. 2003, pp. 2082–92. tional Conference on Ultra-Wideband. [11] E. Garrity, “Getting Smart,” IEEE Power Energy Mag., vol. 9, Mar./Apr. 2008, pp. 38–45. HALID HRASNICA ([email protected])______graduated in 1993 [12] M. Eriksson, “Dynamic Single Frequency Networks,” in electrical engineering from the University of Sarajevo, IEEE JSAC, vol. 19, Oct. 2001, pp. 1905–14. Bosnia and Herzegovina. Afterward, he worked in Ener- [13] M. Mushkin, “A Novel Distributed Synchronized Media goinvest Communications in Sarajevo as developing engi- Access Control Mechanism and Its Applicability to In- neer for communications systems. In 1995 he joined the House Power-Line Networking,” IEEE ISPLC, Malmö, Institute for Telecommunications at Dresden University of Sweden, Mar. 2001. Technology, Germany, where he received his Ph.D. degree [14] M. Lee et al., “HomePlug 1.0 Powerline Communica- in electrical engineering and information technology. Since tion LANs — Protocol Description and Performance February 2006 he has been with Eurescom GmbH in Hei- Results,” Int’l. J. Commun. Sys., vol. 46, no. 5, June delberg, Germany, where he works as programme manag- 2003, pp. 447–73. er for research projects on future telecommunications [15] T. Kwon et al., “Efficient Flooding with Passive Cluster- networks. ing — An Overhead-Free Selective Forward Mechanism for Ad Hoc/Sensor Networks,” Proc. IEEE, vol. 91, no. 8, Aug. 2003, pp. 1210–20.

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ACCEPTED FROM OPEN CALL IMS-Compliant Management of Vertical Handoffs for Mobile Multimedia Session Continuity

Paolo Bellavista, Antonio Corradi, and Luca Foschini, University of Bologna

ABSTRACT bandwidth fluctuations and/or temporary loss of connectivity due to device handoffs, when a The recent advances in wireless client devices mobile node (MN) disconnects from one access and the crucial role of multimedia communica- point (AP) and reconnects to a new one. In par- tions in our society have motivated relevant stan- ticular, granting service continuity during vertical dardization efforts, such as the IP multimedia handoffs is one of the open and crucial problems subsystem, to support session control, mobility, still to overcome, by defining adequate and and interoperability in all-IP next-generation effective support for interoperable session man- networks. IMS has already driven the design of agement. commercial mobile multimedia, but exhibits lim- A large group of standardization entities, ited support for service continuity during hand- which range from the Third Generation Partner- offs. In particular, it omits advanced techniques ship Project (3GPP) to the Internet Engineering to reduce/eliminate handoff delays, especially Task Force (IETF) and Open Mobile Alliance during vertical handoffs (i.e., change of the wire- (OMA), has recently specified the IP multimedia less technology employed by a client to access subsystem (IMS) [1]. IMS defines an overlay the wired Internet, e.g., from UMTS to WiFi). architecture for session control and authentica- We propose an original solution for session con- tion, authorization, and accounting (AAA) in tinuity based on the primary design guideline of all-IP next-generation networks. The main goal cleanly and effectively separating the signaling is achieving openness and interoperability via an plane (for session reconfiguration via SIP) from application-layer approach, mainly by exploiting the media delivery plane (data transmission and the Session Initiation Protocol (SIP). At its cur- related handoff management operations). Our rent stage, however, IMS exhibits some limita- optimized handoff management techniques tions in the support of handoff management. In exploit terminal-based decentralized predictions particular, IMS adopts a reactive approach and to minimize service-level handoff delays. Differ- starts multimedia session reconfiguration only ent from other recent related work, our proposal after losing connection with origin APs, thus fully complies with the standard IMS infra- postponing the execution of data handoff man- structure and works at the application level. The agement operations, which may be articulated, reported experimental results point out that our especially in the case of vertical handoffs. That is solution, available as an open source tool for the prone to produce significant handoff delays and IMS community, reduces playout interruption compromise session continuity. times relevantly by introducing a limited and The article tackles this problem by proposing scalable signaling overhead. a novel solution that exhibits three original characteristics. First, it decouples session signaling INTRODUCTION and data management, by exploiting decentralized handoff predictions that proactively activate A growing number of mobile users require seam- session signaling with the new target network less access to multimedia services, such as while data still flow over the old AP. Second, it audio/video streaming, while they move across is fully compliant with the IMS standard and the available, possibly heterogeneous, wireless does not require any change to already installed infrastructures, spanning from IEEE 802.11 IMS equipment. Third, it applies optimized tech- (WiFi) and Bluetooth (BT) to cellular 3G. How- niques for data management during handoffs to ever, despite the great potential of multimedia minimize data losses. The proposed support 1 Additional information, applications over integrated and heterogeneous infrastructure has been implemented as an open experimental results, and wired-wireless networks, their development and source tool, called the IMS-compliant Handoff the IHMAS prototype deployment are still challenging tasks due to typ- Management Application Server (IHMAS);1 code are available at ically strict QoS requirements (e.g., data arrival IHMAS is available for the IMS community, and http://lia.deis.unibo.it/Res time, jitter, and data losses). In addition, user outperforms related work in the field in terms of ______earch/IHMAS/ mobility introduces demanding issues such as handoff delays and scalability [2–4].

The article is structured as follows. The next • Serving-CSCF (S-CSCF), which is the most section briefly overviews the IMS background and important session control component and The main network- related work. Then we motivate the need for enables the coordinated interaction of all layer operation is the proactive handoff management and propose dif- IMS entities. The S-CSCF receives register ferent techniques to optimize IMS-based handoff. requests from IMS clients, and interacts renewal of network We then present the IHMAS design, implementa- with HSSs to authenticate them, and to configuration tion, and experimental results, while directions of update associations between SIP URIs and our current research conclude the article. current client endpoints. Moreover, parameters at MN: depending on filters/triggers specified by according to the client profiles, the S-CSCF may either route standard IMS SESSION CONTINUITY IN IMS: incoming SIP messages directly to a CN — specification, IHMAS BACKGROUND AND RELATED WORK through the terminating P-/I-CSCF if a CN is in the same/different domain — or for- exploits DHCP to The IMS standard supports different kinds of ward them to an AS [1]. mobility. Our proposal focuses on terminal • Dynamic Host Configuration Protocol re-establish MN IP mobility management during service provisioning (DHCP), the standard Internet facility that address and P-CSCF and, in particular, on vertical handoffs. Hence, IMS employs for MN configuration. server endpoint in in the following we use the term session continu- Given its ability to change SIP message con- ity to indicate specifically multimedia service tent, the S-CSCF can also extend MN-to-CN the target network. continuity in the case of so-called mid-call termi- session signaling paths through the interposition nal mobility with vertical handoffs. of convenient ASs; these ASs may participate in multimedia content adaptation/transport/buffer- IMS BACKGROUND ing by interacting with multimedia proxy (MP) IMS allows the creation, modification, and ter- entities, which play the role of media gateways at mination of service sessions independent of the media delivery plane. ASs are the only points underlying data link layer technologies and of contact between signaling and data transport transport protocols. In particular, IMS promotes planes, and can enforce data handoff manage- the clear separation of the signaling plane — for ment operations by controlling MPs along MN- session re-/configuration, based on all-over-IP to-CN data paths. The IMS client executes at technologies and SIP — and the media delivery the MN; DHCP, P-CSCF, and MPs are deployed plane — for data transmission, based on differ- at the network edges of the MN visited net- ent possible transport protocols, such as IETF works; ASs, HSSs, I-CSCFs, and S-CSCFs typi- Real-Time Transport Protocol over UDP (RTP- cally run in home networks. over-UDP). With a closer view to detail, IMS-based verti- In addition, the IMS infrastructure offers sev- cal handoff management includes several func- eral facilities to help multimedia service develop- tions at different protocol stack layers. At the ers. It not only defines session and AAA data link layer, the crucial operation is data link protocols, but also provides a wide set of support connection, which includes monitoring origin AP functions (e.g., for decentralized proxy-based connection loss and establishing a new connec- session management, endpoint localization, and tion with a target AP. The main network-layer introduction of new IMS-based services/exten- operation is the renewal of network configura- sions [1]). The core IMS functional entities are: tion parameters at an MN: according to the • IMS client, which controls session setup and standard IMS specification, IHMAS exploits media transport by implementing all the DHCP to re-establish the MN IP address and P- SIP extensions specified by IETF and 3GPP CSCF server endpoint in the target network. IMS-related standards. A unique HTTP- Afterward, application-layer session signaling like universal resource identifier (URI), starts. First, an MN establishes a new secure such as sip:user@domain, identifies each association with its S-CSCF by sending a REG- IMS client. Any session is set up between ISTER message through the target P-CSCF. Let two IMS clients (SIP endpoints). In this us note that this is one of the longest handoff article, without losing any generality and for management operations, requiring two round- the sake of presentation clarity, we always trips to fulfill IMS security requirements, and consider an MN as the originating SIP end- lasts about 320 ms [1]. Then the MN renegoti- point and a fixed correspondent node (CN) ates the ongoing session by sending an INVITE as the terminating one. message (about 85 ms), with updated Session • Proxy-call session control function (P- Description Protocol parameters, such as RTP- CSCF), which establishes secure associa- over-UDP MN endpoints and a network descrip- tions with MNs and routes tion. The INVITE message triggers data flow outgoing/incoming SIP messages to the rebinding (and content adaptation when neces- inner IMS infrastructure on an MN’s behalf. sary) at the media delivery plane. • Interrogating-CSCF (I-CSCF), which is Figure 1 shows the standard message flow responsible for securely interconnecting and during IMS-managed handoffs; our original pro- routing SIP messages among different IMS posal is to enhance it via AS interposition, as domains. detailed in the following. Continuous black lines • Application server (AS), which allows the over grey background represent the IMS session introduction of new IMS services and exten- signaling protocol, dotted black lines the local sions by having full control over traversing events emitted by the MN (e.g., old connection SIP dialogs. loss), and solid dark blue ones the data streams. • Home subscriber server (HSS), which stores Let us remark that IMS handoff may incur rela- client AAA data and profiles. tively long delays (up to 2 s) due to its reactive

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liminary: the authors propose MIP usage but do

MN Target P-/I-CSCFMN S-CSCFMN S-CSCFCN CN not face at all the challenging issues of real- Old conn. world handoff latencies. loss Data flow Networking Context-Aware Policy Environ- ment (NetCAPE) also supports 3G-to-WiFi ver- Datalink tical handoffs. It adopts a cellular-centric handoff and solution by employing the so-called tight-cou- DHCP req. pling interworking scheme of 3GPP [3]. Similar (1) REGISTER (2) REGISTER to our proposal, NetCAPE exploits handoff pre- (3) 401 Unauth. diction to proactively activate vertical handoff (4) 401 Unauth. procedures before clients lose connectivity from (5) REGISTER (6) REGISTER phase their origin APs. However, its tight-coupling

(8) 200 OK (7) 200 OK Registration approach requires that any communication from (9) INVITE the WiFi domain passes through the core cellu- (10) INVITE

Media loss (11) INVITE (12) INVITE lar network, with increased communication costs. Moreover, NetCAPE focuses on handoff Data flow prediction and MIP delay optimization, but not rebind

phase on full compliance with the standard IMS infra- (14) 200 OK (13) 200 OK structure. (16) 200 OK (15) 200 OK Renegotiation To the best of our knowledge, the published Data flow solution closest to IHMAS is [4], which enables secure session continuity for the multimedia domain (MMD), the IMS-equivalent infra- Figure 1. Message flow for non-optimized IMS handoff management. structure defined by the 3GPP2 standard. MMD aims to reduce handoff latency by employing context transfer techniques to move, either reac- approach: handoff is triggered by the loss of the tively or proactively, session description and old connection, and all the subsequent opera- security information from old to new P-CSCFs, tions are performed sequentially, without exploit- and addresses all MIP-related security issues [4]. ing the possible overlapping between the Nonetheless, it is not easily deployable in the coverage areas of the old and target APs. IMS infrastructure: it requires modifying the standard IMS session signaling protocol to sup- RELATED WORK port session context transfer and consistently Application-layer IMS-based handoff manage- changing existing P-CSCFs. In addition, MMD ment has its roots in SIP-based mobility manage- operates data handoff (MIP address reconfigura- ment, first proposed by Schulzrinne [5]. tion) before multimedia session renegotiation, Thereafter, a number of SIP-based research thus precluding multimedia flow adaptation efforts tackled session continuity by addressing before data transfer. Finally, the proposed pro- two main issues: totype employs MIPv4, thus possibly undertaking • Session reconfiguration, usually managed at long latencies due to triangular routing and, con- the application layer with SIP sequently, long handoff delays [4]. • Seamless flow provisioning and data path rebinding, managed at either the application layer through SIP rebinding or, more IHMAS APPLICATION-LAYER often, the network layer via Mobile IP ANDOFF NHANCEMENTS (MIP) and its extensions [6] H E The interest in IMS-based session continuity As exemplified in the previous section, providing is also demonstrated by the recent special issue session continuity of IMS-based mobile multime- of this magazine on IMS infrastructures and ser- dia is still an open issue. About session signaling, vices [7]. In the following, for the sake of brief- one of the most challenging problems is to ness, we only focus on the three vertical handoff reduce the duration of session rebinding. In fact, solutions closest to IHMAS, ordered by growing the rebinding of ongoing sessions requires similarity. exchanging several SIP REGISTER/INVITE mes- Intelligent Network-Seamless Mobility Access sages (usually called re-REGISTER and re- (IN-SMA) mainly focuses on session reconfigu- INVITE), thus lengthening data handoff delays. ration [2]. In particular, IN-SMA introduces an Some support solutions in the literature face this IMS AS, called the mobility server, that supports issue by introducing extensions to deal with con- voice call (re)routing from 3G cellular networks text transfer [4]. However, these solutions are to IMS-compliant WiFi VoIP infrastructures, not standard; their deployment requires protocol while providing seamless flow provisioning via stack changes at all CSCFs, and their main goal MIP. Like our approach, IN-SMA considers is not session continuity. For instance, MMD mobility as an advanced IMS service (imple- does not allow data adaptation before data mented as an IMS AS) and does not require handoff, and this may cause the injection into changes to the IMS core. However, it presents the target network of multimedia flows with two main limitations. First, IN-SMA supports quality exceeding its transmission capabilities, vertical handoffs only in the 3G-to-WiFi direc- thus possibly congesting it up to data delivery tion, and excludes decentralized, terminal-based, interruption. and proactive MN initiation of handoff manage- About data handoff management, current ment countermeasures. Second, the proposed proposals tend to be MIP-based and with still solution for flow continuity seems to still be pre- unsolved issues. First, the MIP network layer

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approach lacks the visibility of (and hardly com- the duplication (and simultaneous transmission) plies with) application-specific requirements of multimedia flows over multiple wireless inter- The proposed such as maximum tolerable delay. Moreover, faces in the last wired-wireless hop. For hard there is a growing interest in soft data handoff proactive handoff, instead, the second-level IHMAS optimizations strategies because they permit MNs to have two buffer can receive and store all the incoming are lightweight and or more simultaneous connections to various packets that would be lost during the (short) may easily apply also APs, as opposed to hard strategies where MNs RTP-over-UDP rebinding period and enable have only one connection at a time. MIP-based local retransmission of stored packets (forward- to uplink data solutions typically adopt a hard handoff strategy ing) when the MN reconnects to the MP over transmissions by only that maps one MN to only one IP address, by the target AP. The hard reactive handoff strate- excluding more flexible rebinding opportunities. gy is a simplified case of hard proactive with no requiring limited Finally, for each vertical handoff, MIP and data store-and-forward. Finally, let us observe buffering resources MIPv4 require an additional round-trip time (in that in the following, we focus only on the down- at the client side, addition to the ones due to REGISTER/INVITE link direction (from APs to wireless clients) messages) to reconfigure data endpoints at the because most traffic load is in this direction in i.e., to cover only the MN home (i.e., home agents). multimedia streaming applications such as video handoff disconnec- Our IHMAS proposal overcomes all the on demand and IP-based TV. Anyway, the pro- above limitations by adopting three main design posed IHMAS optimizations are lightweight and tion interval, usually guidelines. First, our solution is fully IMS-com- may easily also apply to uplink data transmis- available at any pliant: IHMAS originally exploits IMS separa- sions by only requiring limited buffering portable client device tion of signaling/media delivery planes and resources at the client side (i.e., to cover only introduces a new AS to realize advanced data the handoff disconnection interval), usually nowadays. handoff management. In that way, the proposal available on any portable client device nowadays. is fully compatible with the current IMS stan- The remainder of the section presents our dard, without the need for any intervention on original IMS handoff optimizations. While all already deployed IMS components. Second, our IHMAS enhancements adopt a proactive solution is proactive: to reduce vertical handoff approach on the IMS session signaling plane, we latency, IHMAS predicts vertical handoffs at distinguish different types of IHMAS improve- clients and starts session reconfiguration before ments depending on how the ASSC exploits its handoff management. Third, our proposal adopts awareness of vertical handoff temporal proximity an application layer proxy-based approach, not — through (re-)INVITE reception from MN — only for session signaling, but also for data hand- to trigger different management actions at the off. IHMAS overcomes typical MIP problems by media delivery plane: hard reactive/proactive using SIP-based flow rebinding and exploiting and soft data handoff management. MPs that are locally deployed at client access localities to enable prompt, flexible application- IHMAS HARD DATA HANDOFF MANAGEMENT layer handoff management on the media deliv- Figure 2 shows our optimized hard ery plane. proactive/reactive handoff procedures. Dashed By focusing on session signaling, proactivity is black lines represent our original message flow based on the introduction of a vertical handoff extensions and red brackets point out the opera- predictor (VHP) that extends the IMS client by tions that the MP executes only for proactive providing lightweight and completely decentral- management. VHP predictions enable the proac- ized prediction via only local access to client tive execution of data link/network handoff wireless interfaces. The IMS client exploits VHP operations over the target network: they permit predictions to proactively start SIP-based session completing the registration phase and starting reconfiguration (REGISTER/INVITE messages) renegotiation while keeping the media flows over the target AP while continuing to receive active over old connections. In particular, upon multimedia data from the origin AP. On the INVITE message reception (step 12), depending IMS infrastructure side, the primary IHMAS on the adopted handoff strategy, the ASSC trig- component is the AS for session continuity gers data handoff at the MP by either activating (ASSC) that reduces handoff media losses by (proactive) or not (reactive) the store-and-for- decoupling session rebinding and data transfer ward function on multimedia flows (step 13). times. Deployed at the MN home network, the For proactive handoff, the MP receives and ASSC receives all SIP messages from the MN S- stores incoming flows in its local second-level CSCF; it acts as an IMS anchor point, by hiding buffer during the RTP-over-UDP rebinding peri- CN from MN mobility and consuming all hand- od, while the IMS client supports session conti- off-related SIP messages (especially INVITE); nuity by consuming the client-side buffer. Thus, finally, it triggers data handoff control opera- after data rebinding, the MP can promptly fill up tions over the MP. MN buffers by retransmitting all the data other- The MP component implements our novel wise lost due to temporary disconnection. handoff management strategies for either soft or Therefore, hard proactive management hard (the latter either reactive or proactive) requires that the MN sends a message to trigger handoff management. In particular, we propose data retransmission. RTP retransmissions were a flexible two-level buffering solution: the MP, standardized only recently and some IMS clients deployed along the MN-to-CN multimedia data do not yet support this facility, as well as RTP path, hosts one second-level buffer for each MN data frame reordering to present retransmitted currently active in its domain to suitably adjust frames in the correct order to multimedia play- multimedia flows with the main goal of service ers [8]. To guarantee the widest interoperability, continuity [6]. The second-level buffer enables in addition to the more effective hard proactive soft handoff management by locally supporting strategy, IHMAS provides hard reactive handoff.

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maintaining the old interface active for only the

MN Target P-/I-CSCFMN MP S-CSCFMN ASSC CN short time necessary to receive the first packets Handoff over the new interface, usually below 220 ms. prediction IHMAS soft handoff adopts a proactive session signaling approach and is completely IMS-com- Datalink handoff and DHCP req. pliant: it solely requires minor modifications at IMS clients, only affecting media delivery mod- (1) REGISTER (2) REGISTER ules. (4) 401 Unauth. (3) 401 Unauth. By delving into finer detail, at INVITE mes- (5) REGISTER (6) REGISTER sage reception, the ASSC activates soft handoff (8) 200 OK (7) 200 OK at the MP (step 13). Hence, the MP duplicates (9) INVITE and sends RTP frames over both old and target (10) INVITE (13) Hard (11) INVITE (12) INVITE (proactive)/ wireless links. The IMS client is in charge of reactive data handoff removing duplicated frames. The interaction trigger ends at the completion of RTP-over-UDP con- Proactive data buffering Data flow rebind nection rebinding. To stop data flow duplication Old Data flow at the MP, IHMAS introduces a new control conn. loss message from MN to MP by adding an optional (14) 200 OK field to the standard RTP retransmission pay- (16) 200 OK (15) 200 OK (17) 200 OK load format (step 18) [8].

(18) Client Lost frames re-transmit Lost data retransm. request IHMAS TESTBED IMPLEMENTATION reactive mng.

Media loss for Data flow AND PERFORMANCE RESULTS

Figure 2. Message flow for optimized hard reactive/proactive data handoff To thoroughly test and evaluate the performance management. of IHMAS, we carried out two types of experiments by deploying it in the widescale and heterogeneous wireless network at our campus. First, we performed field experiments validating Hard reactive handoff may also be useful, in the effectiveness of IHMAS functions. Second, some cases, to minimize the exploitation of sec- we used a state-of-the-art IMS traffic generator ond-level buffer resources. However, that buffer- to assess the cost and scalability of the proposed ing cost is usually very low; in fact, it depends on signaling by emulating the typical behavior single multimedia frame size, data rate, and expected in wide-area IMS deployments with a especially RTP-over-UDP rebinding time, usual- multitude of concurrent users/requests. ly below 220 ms even in high-load scenarios such In the evaluation testbed, the IMS infra- as the ones discussed below. In addition, let us structure components (CSCFs, HSSs, and note that hard handoff strategies should apply ASSC) run on Linux boxes with two 1.8 GHz only if compatible with application-specific CPUs and 2048 Mbytes RAM, following the requirements on delay and data loss; otherwise, standard IMS deployment indicated earlier. soft handoff has to be selected. During the first experiment, MNs (Windows Our proposal does not require any modifica- and Linux laptops equipped with OrinocoGold tion to the standard IMS protocol (grey back- WiFi cards and MopogoBT dongles) moved ground), but only adds some new messages between BT and WiFi cells served by (steps 13 and 18) to link signaling session and MopogoBT dongles and CiscoAironet1100 APs, media delivery planes. Different from MMD, we respectively, changing to several access net- do not postpone session renegotiation after data works corresponding to different university handoff; in this way, IHMAS can tailor multime- buildings. For the second experiment, instead, dia flows to target network characteristics before we employed the IMS Bench SIPp, an IMS transferring them, by granting session continuity traffic generator that conforms to the ETSI TS and flow delivery at the most suitable quality at 186 008 IMS/NGN Performance Benchmark any time [4]. To activate flow adaptation at the specification. For IMS implementation, we MP proactively, the ASSC exploits Session employed the OpenIMSCore that includes all Description Protocol data in INVITE messages. main IMS components and various facilities to ease S-CSCF trigger creation as well as the IHMAS SOFT DATA HANDOFF MANAGEMENT integration of new ASs [9]. The ASSC is imple- Figure 3 shows the optimized soft handoff pro- mented in Java, by exploiting the portable Java cedure implemented by IHMAS. Compared to application programming interface (API) for hard handoff, soft handoff supports a wider Integrated Networks (JAIN) SIP implementa- range of multimedia services, even with stricter tion by the National Institute of Standards and delays and jitter requirements. It requires small- Technology. Our MNs exploit the open source er second-level buffer resources, only to store IMS Communicator — a pure Java IMS client the short streaming data chunk necessary to sus- based on SUN Java Media Framework (JMF) tain streaming; for instance, for a G.711 (U-law) and JAIN SIP with IMS SIP extensions by encoded audio flow with constant frame rate = 3GPP and IETF — that we originally extended 50 frame/s and G.711 RTP packet payload size to support IHMAS optimizations [6, 10]. For of 216 bytes, it is sufficient to store three data data buffering/streaming, our MP exploits frames (less than 1 kbyte). In addition, it slightly Asterisk, the widespread open source telephony increases energy consumption at the client by engine that we extended to support second-

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level buffering [6]; the related performance

evaluation at the media delivery plane is out of MN Target P-/I-CSCFMN MP S-CSCFMN ASSC CN the scope of this article. Handoff The results of the first set of experiments, prediction shown in Fig. 4, point out the effectiveness of Datalink handoff IHMAS handoff management techniques by and DHCP req. comparing their performance in the case of ver- (1) REGISTER tical handoffs from BT to WiFi. Reported results (2) REGISTER are averaged over 1000 handoff cases, while pro- (4) 401 Unauth. (3) 401 Unauth. visioning an audio on demand service offering (5) REGISTER (6) REGISTER G.711 (U-law) encoded flows (constant frame (7) 200 OK rate = 50 frames/s) with buffer slots storing (8) 200 OK G.711 RTP packets (216-byte payload/packet). (9) INVITE (10) INVITE (11) INVITE (12) INVITE (13) Soft For each handoff management scenario, the fig- data handoff ure shows session signaling duration (upper bar), Data flow over trigger data handoff management delay (defined as the old connection delivery delay introduced by the applied handoff technique, middle bar), and playout interruption Duplicates Data flow elimination duplication and bind time (defined as the data duration of the media (14) 200 OK gap perceived by final users, lower bar); the Ø (16) 200 OK (15) 200 OK symbol represents negligible time intervals. Fig- (17) 200 OK ure 4 focuses on a restricted time interval exclud- Data flow over target connection ing VHP prediction: as known from our previous Old conn. (18) Stop experiments, our BT-to-WiFi handoff prediction loss data grants a prediction advance time between 5.4 s duplication and 6.8 s with sufficiently low error rates (under 9.0 percent) for most mobility conditions of Figure 3. Message flow for optimized soft data handoff management. interest for multimedia streaming [6]. By focusing on session signaling, the reported result is the sum of the duration of the four main vertical handoff functions: data link connection, DHCP negotiation, REGISTER, and Basic handoff INVITE signaling times. Data link connection management time strictly depends on handoff type, wireless Hard reactive coverage, and client card characteristics [6]. For handoff management basic handoff scenarios, it is very long (e.g., 670 Data link connection Hard proactive DHCP renegotiation ms), due to the employed reactive approach, handoff 0 REGISTER signaling which activates the target WiFi network and management INVITE signaling starts data link discovery only after connection Soft handoff Minimum service delay 0 loss. In all other situations, instead, IHMAS management 0 Playout interruption exploits VHP predictions to switch proactively to 0 200 400 600 800 1000 1200 1400 1600 1800 2000 WiFi as soon as a probable handoff is predicted, Time (ms) thus eliminating discovery delays and dropping data link connection time to 16 ms. DHCP nego- Figure 4. Session signaling and data handoff completion time for BT to WiFi tiation time highly depends on DHCP handoff. server/client implementation. We have extensively tested both Windows and Linux servers, and decided to employ Linux dhcpd due to its management delay and playout interruption. In robustness. Moreover, while in the basic handoff basic handoff, due to the serialization of handoff management case DHCP negotiation imposes operations, RTP connection rebinding can start long delays (535 ms), our optimized techniques only after session signaling termination, thus accelerate the process by promptly activating causing heavy data management delays (1812 DHCP discovery as soon as the new interface is ms). Our hard handoff management drops this active (delay down to 206 ms). Finally, to better delay down to 220 ms, which corresponds to the evaluate REGISTER and INVITE times when time required to send the INVITE message and compared with basic handoff, we do not include to finish RTP connection rebinding, started as the delay introduced by the distance between soon as MP receives the ASSC handoff trigger. CN and MN home networks because the ASSC Moreover, if second-level buffering is used, it is reconfigures the session directly at the MN possible to mask the deriving loss of multimedia home. Under that assumption, the measured data to final users at the expense of increased REGISTER and INVITE signaling times are sim- packet delays (due to data buffering), thus avoid- ilar for all handoff management situations: 327 ing any playout interruption. In addition, we ms and 85 ms, respectively, as expected due to have performed preliminary experiments for the adoption of the standard IMS session signal- WiFi-to-3G vertical handoff, and the collected ing. The measurements exhibited a limited vari- results have demonstrated the same trends of ance (under 7.5 percent in all cases). Fig. 4. The only main difference is a much longer The reported results clearly show that our data link connection time (from 7.3 s without proactive approach can relevantly reduce session optimizations to 4.2 s by properly decreasing the signaling time. In addition, even most important, wakeup period of 3G cards in idle state), while it is demonstrated to be very effective for data the duration of other phases is approximately

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the same. In particular, handoff prediction (in ing/media plane decoupling and application this case measuring the possibility that WiFi sig- layer approach [4]. nal strength at the MN drops below a given Figure 5 reports the results of the second set threshold) permits very low latencies to be of experiments, aimed at quantitatively evaluat- achieved, as reported in Fig. 4 for the BT-to- ing costs and scalability of ASSC interposition in WiFi case. Regarding IHMAS soft handoff man- IHMAS in wide-scale deployment scenarios and, agement, it supported lossless handoffs without more generally, of signaling overhead due to AS any additional frame delay cost in all the experi- interposition in IMS. By using the IMS Bench ments. Finally, let us note that the performance SIPp and exploiting the concept of IMS session results in Fig. 4 largely outperform other state- phases supported in it, we defined a scenario of-the-art solutions in the literature (e.g., the consisting of a first preparation phase, which lowest MMD playout interruption time is 3666 lasts 330 s and includes only IMS client registra- ms). Such an improvement is possible because tions with a constant arrival rate of 15 calls per IHMAS can eliminate data link connection and second (cps), and a second evaluation phase, MIP reconfiguration times, thanks to its signal- which consists of a mix of 2.5 percent registra- tions, 2.5 percent deregistrations, 15 percent reregistrations, 50 percent invitations, and 30 220 percent re-invitations. That mix mimics the usual 10 cps 20 cps 30 cps 40 cps 50 cps 60 cps 70 cps 200 IMS traffic composition. The evaluation phase is configured with 7 incremental steps of traffic, 180 going from 10 cps to 70 cps; each step (from 330 160 S-CSCF s to 750 s) lasts 60 s, and calls arrive according 140 P-CSCF3 to a Poisson distribution. 120 Delving into finer detail, we first stressed the system without the ASSC within the path (Fig. CPU % 100 5a); then we repeated the experiments by inter- 80 posing the ASSC and activating new IMS com- 60 ponents to grant an infrastructure scalability 40 level comparable to the one obtained without 20 the ASSC (Fig. 5c). For the sake of simplicity, here we focus on the most overloaded compo- 0 330,000 390,000 450,000 510,000 570,000 630,000 690,000 750000 nents, the S-CSCF, P-CSCF, and ASSC. Report- (a) ms ed results show CPU utilization (from 0 to 200 percent, summing up the two CPUs) because, in 100,000 our experience, the CPU is the main bottleneck 10 cps 20 cps 30 cps 40 cps 50 cps 60 cps 70 cps in IMS infrastructures due to the costs of message parsing/forwarding. Other performance INVITE w/o ASSC indicators, such as memory and network load, 10000 INVITE with ASSC have proven less relevant to scalability (additional results are available at the IHMAS web site). We also report the delay of the first INVITE sig- 1000 naling phase — the longest one (after the initial ms unchanged REGISTER) due to initial filtering criteria evaluation at S-CSCF and ASSC interposition, common to all IHMAS handoff strategies. 100 This delay is reported with and without ASSC (dashed and solid lines in Fig. 5b, respectively, in logarithmic scale). All results have exhibited lim- 10 ited variance (i.e., under 5 percent for 100 runs). 330,000 390,000 450,000 510,000 570,000 630,000 690,000 750,000 Without the ASSC, we have determined that (b) ms to stir one S-CSCF (solid line in Fig. 5a) to its upper limit, it is necessary to deploy three P- 220 CSCFs (dashed line; we report only P-CSCF3 10 cps 20 cps 30 cps 40 cps 50 cps 60 cps 70 cps 200 for sake of clarity). The S-CSCF starts collapsing 180 S-CSCF at 610 s (Fig. 5a), as also shown by the sudden P-CSCF3 increment of the INVITE delay. At step 6, the 160 ASSC IMS Bench stops injecting new traffic due to the 140 number of received errors and S-CSCF satura- 120 tion also provokes a message retransmission cas- CPU % 100 cading effect on P-CSCFs, which collapse in the 80 following step (Figs. 5a and 5b). ASSC interposition produces a non-negligible message load 60 increase: each traversing SIP message provokes 40 the creation and injection of an additional SIP 20 message. However, to have performance results 0 comparable to the ones without the ASSC, it is 330,000 390,000 450,000 510,000 570,000 630,000 690,000 750,000 easy to activate an additional S-CSCF to split (c) ms and balance incoming load. With this simple deployment variation, the S-CSCF begins to sat- Figure 5. IHMAS session signaling scalability. urate at 530 s and IHMAS collapses at step 5,

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with a cascading effect on the P-CSCF and ASSC REFERENCES (Fig. 5c; the other S-CSCF exhibits a similar [1] G. Camarillo and M. A. García-Martín, The 3G IP Multi- The IHMAS research behavior). The ASSC, instead, does not show media Subsystem (IMS), 2nd ed., Wiley, 2006. work demonstrates any scalability issues: before system collapse, its [2] C. Kalmanek et al., “A Network-Based Architecture for CPU load is always below 80 percent. Seamless Mobility Services,” IEEE Commun. Mag., vol. the suitability of an In short, on one hand, the reported results 44, no. 6, June 2006, pp. 103–9. [3] A. Udugama et al., “NetCAPE: Enabling Seamless IMS application-level quantitatively show the non-negligible cost of AS Service Delivery across Heterogeneous Mobile Net- interposition in any IMS infrastructure in gener- works,” IEEE Commun. Mag., vol. 45, no. 7, July 2007, approach to extend al. On the other hand, they demonstrate that pp. 84–91. the standard IMS IHMAS scales well and can apply even to [4] A. Dutta et al., “Mobility Testbed for 3GPP2-Based Mul- timedia Domain Networks,” IEEE Commun. Mag., vol. infrastructure in deployment scenarios with high cps. Let us stress 45, no. 7, July 2007, pp. 118–26. that in realistic execution environments, IHMAS [5] H. Schulzrinne, E. Wedlund, “Application-Layer Mobility order to improve its Using SIP,” ACM Mobile Comp. Commun. Rev., vol. 4, optimization costs apply only to a subset of performance for incoming calls (in our experiments we consid- no. 3, July 2000, pp. 47–57. [6] P. Bellavista et al., “Context-Aware Handoff Middleware session mobility ered all calls to rapidly stress our system); more- for Transparent Service Continuity in Wireless Net- over, they are expected to be balanced by proper works,” Pervasive Mobile Comp. J., vol. 3, no. 4, Aug. during handoffs. pricing. 2007, pp. 439–66. In addition, we did analogous performance [7] M. Toy, H. J. Stuttgen, and M. Ulema, “IP Multimedia Systems in Infrastructure and Services — Part II,” IEEE evaluations (both sets of experiments) for the Commun. Mag., Special Issue on IP Multimedia Systems other vertical handoff direction (i.e., from WiFi and Services, vol. 45, no. 7, 2007, pp. 66–67. to BT): apart from longer BT data link connec- [8] J. Rey et al., “RTP Retransmission Payload Format,” IETF tion delays, IHMAS enabled similar delay reduc- RFC 4588, July 2006. [9] Open IMS Core Project; http://www.openimscore.org/ tions in that case as well. For this reason, due to [10] IMSCommunicator Project; http://imscommunicator. space limitations, here we do not report those ______berlios.de/ results, which are available at the IHMAS Web site, together with further implementation details BIOGRAPHIES and performance evaluations. PAOLO BELLAVISTA [SM] ([email protected])______graduated from the University of Bologna, Italy, where he received a Ph.D. degree in computer science engineering in 2001. He CONCLUSIONS is now an associate professor of computer engineering at The IHMAS research work demonstrates the the University of Bologna. His research activities span from mobile-agent-based middleware solutions and pervasive suitability of an application-level approach to wireless computing to location/context-aware services and extend the standard IMS infrastructure in order adaptive multimedia. He is a senior member of ACM. He is to improve its performance for session mobility an Editorial Board Member of IEEE Communications Maga- during handoffs. In particular, IHMAS flexibly zine and IEEE Transactions on Services Computing. supports three data handoff management strate- ANTONIO CORRADI [M] ([email protected])______graduated gies that an ASSC can dynamically select and from the University of Bologna and received an M.S. in configure depending on service requirements electrical engineering from Cornell University, Ithaca, New and deployment conditions. That is possible by York. He is a full professor of computer engineering at the University of Bologna. His research interests include dis- preserving full compliance with the standard, tributed and parallel systems and solutions, middleware for thus enabling the IHMAS deployment over pervasive and heterogeneous computing, infrastructure already installed IMS-conformant networks. support for context-aware multimodal services, network The encouraging results obtained with the management, and mobile agent platforms. He is a member of the ACM and the Italian Association for Computing IHMAS prototype are motivating our current (AICA). research along two primary directions. On one hand, we are executing objective measurement LUCA FOSCHINI [M] ([email protected])______graduated from of quality improvements/degradations during the University of Bologna, where he received a Ph.D. degree in computer science engineering in 2007. He is now vertical handoffs with/without multimedia adap- a research fellow of computer engineering at the University tation at the MP. On the other hand, we are of Bologna. His interests include distributed systems and using IHMAS to implement an IMS-based phone solutions for pervasive computing environments, system meeting application for mobile users (support of and service management, context-aware session control and adaptive mobile multimedia, and mobile-agent-based group communications). middleware solutions. He is a member of AICA.

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ACCEPTED FROM OPEN CALL Reputation Estimation and Query in Peer-to-Peer Networks

Xing Jin, Oracle USA S.-H. Gary Chan, HKUST

ABSTRACT unstructured P2P file sharing systems are highly vulnerable if attackers insert massive bogus Many peer-to-peer systems assume that peers records to poison search indexes. are cooperative to share and relay data. But in To detect malicious peers or reward well the open environment of the Internet, there may behaved ones, a reputation system is often used. be uncooperative malicious peers. To detect In a typical reputation system each peer is malicious peers or reward well behaved ones, a assigned a reputation value according to its per- reputation system is often used. In this article we formance history. Differentiated services are give an overview of P2P reputation systems and then provided to peers according to their reputa- investigate two fundamental issues in the design: tion. While the basic idea is simple, a practical reputation estimation and query. We classify the system design is not easy. Generally, a P2P repu- state-of-the-art approaches into several cate- tation system consists of three functional compo- gories and study representative examples in each nents [2]: collecting information on peer category. We also qualitatively compare them behavior, scoring and ranking peers, and and outline open issues for future research. responding based on peers’ scores. All these components are nontrivial, especially given the INTRODUCTION following consideration: • Scalability: A large P2P network may have In recent years peer-to-peer (P2P) systems have hundreds of thousands of peers. For exam- seen enormous success and rich developments ple, Skype has several million online users. over the Internet. Typical applications include A reputation system should be highly scal- file sharing, streaming, Internet telephony, and able in terms of peer number. overlay routing. According to CacheLogic • Adaption to peer dynamics: Peers may join Research, in 2006 P2P traffic accounted for over or leave at any time. If reputation informa- 72 percent of Internet traffic that year. tion is maintained at peers, peer leaving In P2P systems cooperative peers self-orga- may lead to information loss. A robust rep- nize themselves into overlay networks and store utation system should take peer dynamics or relay data for each other. Many P2P systems into account. work on the assumption of truthful cooperation • Security: Malicious peers may endeavor to among peers. However, in the open environment break down the reputation system so that of the Internet, some participating peers may they can conduct malicious actions without not cooperate as desired. They may be selfish being detected. For example, peers may and unwilling to upload data to others, or they purposefully leave and rejoin the system may have abnormal actions such as frequent with a new identity in order to shed any rebooting that adversely affect their neighbors. bad reputation [2]. Clearly, a good reputa- More seriously, some peers may launch attacks tion system should be secure to resist these to disrupt service or distribute viruses in the adversarial behaviors. overlay network. We call all these uncoopera- In this article we study two fundamental issues tive, abnormal, or attacking behaviors malicious in P2P reputation systems. actions and the associated peers malicious peers. Reputation estimation: An estimation method Malicious peers may seriously degrade the describes how to generate peer reputation based performance of P2P networks. Liang et al. have on others’ feedback. We classify existing estima- tracked several attacking behavior in practical tion methods into three categories: social net- P2P file sharing systems [1]. They find that more work, probabilistic estimation, and than 50 percent of copies of popular songs in game-theoretic model. We select representative KaZaa are polluted, meaning that the content examples from each category, and discuss their downloaded from the network is different from advantages and limitations. As many estimation This work was supported, the downloader’s expectation (e.g., the content is methods rely on specific feedback collection in part, by the Hong Kong corrupt and cannot be played, or the content is a mechanisms, we also discuss feedback collection Innovation and Technol- different song from the search index metadata). mechanisms when necessary. ogy Fund (ITS/013/08). Their study also shows that both structured and Reputation query: Reputation query in P2P

networks is not trivial. First, efficient data stor- generates, the smaller weight in reputation com- age and retrieval is always a challenging issue in puting its feedback has. Similarly, in [5] a peer’s The correlated P2P networks. Huge amounts of data require reputation is computed as a weighted average of reputation model is distributed storage approaches. Then efficient feedback from direct witnesses of its perfor- retrieval becomes nontrivial. Peer dynamics mance. Xiong et al. develop a general reputation more like our real bring more difficulty. Second, reputation data model, which considers, for example, feedback social network, are highly security-sensitive. The reputation of a from peers, the trustworthiness factor of feed- peer cannot be locally stored at the peer itself, back sources, and the transaction context factor where third-party because a dishonest peer may misreport its repu- for discriminating transaction importance [6]. peers can express tation value in order to gain rewards or avoid Almost all separated reputation models can be their opinion on a punishments. We also need to consider security expressed by this model. issues in reputation delivery. In this study we In a correlated reputation model the reputa- peer. But it takes survey the state-of-the-art approaches to reputation of a peer is computed based on the opinion more cost to collect tion storage and retrieval in P2P networks. We of its direct transaction partners as well as third- classify them into three categories. For each cat- party peers. In this model a peer, A, who wishes and aggregate egory, we discuss illustrative examples. We also to know the reputation of another peer, B, can third-party opinion. qualitatively compare them and outline possible ask some peers (e.g., its neighbors) to provide For example, directions for future research. their opinion on B (although some of the peers There are many other important issues in may not have conducted any transaction with EigenTrust takes a P2P reputation systems; for example, how to B). A then combines peer opinions to calculate long time to wait prevent targeted and adversarial attacks? How B’s reputation. We take EigenTrust as an exam- to interpret reputation? Interested readers may ple [7]. In EigenTrust, whenever a peer confor reputation values refer to [2, 3] for a comprehensive overview of ducts a transaction with another peer, they keep to converge. P2P reputation issues. reputation values for each other. If there is no The rest of the article is organized as follows. direct transaction between two peers, they keep In the next section we explore the reputation a zero reputation value for each other. Peers estimation issue. We then discuss reputation then iteratively update the reputation values. query techniques. We conclude in the final sec- Each time peer A wishes to update the reputation. tion of peer B, A asks for B’s reputation from all other peers in the system. A then computes a EPUTATION STIMATION weighted sum of these reputation values and R E keeps the result as the new reputation of B. In There are mainly three reputation estimation each iteration all peers conduct the above repu- methods in current P2P networks. The first one tation update. The process continues until the is the social network, where all feedback avail- reputation values kept at different peers con- able in the network are aggregated to compute verge. Another example is the network informa- peer reputation. The second one is probabilistic tion and control exchange (NICE) reputation estimation, which uses sampling of the globally model [8]. Each peer holds the reputation of its available feedback to compute peer reputation. transaction partners according to the quality of The third one is the game-theoretic model, transactions. All peers further form a trust which assumes that peers have rational behavior graph based on reputation values. Later on, an and uses game theory to build a reputation sys- overlay path between two peers is selected as tem. We elaborate on these methods below. the most trustworthy path between them in the trust graph. SOCIAL NETWORK The correlated reputation model is more like Approaches based on the social network can be our real social network, where third-party peers further divided into two categories: separated can express their opinion on a peer. But it costs reputation model and correlated reputation model. more to collect and aggregate third-party opin- In a separated reputation model only the direct ion. For example, EigenTrust takes a long time transaction partners of a peer (e.g., resource to wait for reputation values to converge. provider/downloader or streaming neighbor) can express their opinion on the reputation of the PROBABILISTIC ESTIMATION peer. A practical example is the eBay reputation This approach uses sampling of the globally system (although eBay is not a P2P network). available feedback to compute peer reputation. After each transaction at eBay, the buyer and It usually relies on some assumptions on peer the seller rate each other with positive, negative, behavior. For instance, it may assume that a or neutral feedback. The reputation is calculated peer is trustworthy with a certain but unknown at a central server by assigning 1 point for each probability. And when sharing its own experi- positive feedback, 0 point for each neutral feed- ence with others, a peer may lie with some, back, and –1 point for each negative feedback. again unknown, probability [9]. It then uses The reputation of a participant is computed as probabilistic estimation techniques to estimate the sum of its points over a certain period. Con- all unknown parameters. Many estimation meth- sidering that peers may lie in their feedback, ods may be used. Despotovic et al. use maximum Mekouar et al. propose to monitor suspicious likelihood estimation, which assumes that peers feedback [4]. That is, after each transaction do not collude [9]. Mui et al. use Bayesian esti- between a pair of peers, both peers are required mation, which uses only direct interaction among to generate feedback to describe the transaction. peers and does not use third-party opinion [10]. If there is an obvious gap between the two pieces By using a small portion of the globally avail- of feedback, both are regarded as suspicious. able feedback, the probabilistic model has lower Later on, the more suspicious feedback a peer cost in feedback collection than the social net-

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CENTRALIZED AND [55, 80) R PARTIALLY CENTRALIZED STRUCTURES

Step 1 The simplest solution is to use a powerful server Step 2 to keep the reputation of all peers. For example, eBay uses a central server to collect and keep all [95, 1000] [20, 40) users’ reputations. Feedback from users is sent to and stored at the server. A query of a user’s Step 2 reputation is also sent to and answered by the server. Similar approaches have been used in [13]. T [0, 20) [40, 55) [80, 95) A centralized approach is easy to implement and deploy. Security of a central server is much easier to achieve than that of distributed components in a distributed approach. Furthermore, in Step 3 a centralized approach, reputation management is independent of peer joining and leaving, which B Step 4 greatly simplifies reputation retrieval. However, a centralized approach is not scalable to large P2P networks. Also, the server forms a single A point of failure, making the system vulnerable. To address the limitations of the centralized approach, a partially centralized approach, which Proxies uses a set of servers instead of a single server, has been proposed. Mekouar et al. propose a Streaming peers malicious detector algorithm (MDA) to detect malicious peers in KaZaa-like systems [4]. KaZaa is a partially centralized P2P file sharing Figure 1. Process of submitting a report about a streaming peer A by its child B system with a set of supernodes. Each ordinary for the ﬁrst time in a proxy-based approach (from [5]). Step 1) B sends A's IP peer is attached to a unique supernode. MDA address to R. Suppose that A's IP address is represented by a numerical value assumes that supernodes are all trustworthy and 88. Step 2) R searches in the binary tree to identify the proxy that manages 88 maintain reputation information for ordinary (T in this case). Step 3) T responds to B with its certiﬁcate. Step 4) After veri- peers. All evaluation results about a peer are fying the trustworthiness of T, B sends its report about A to T. maintained at its attached supernode. Supern- odes can then enforce differentiated service to peers according to their reputation. work approach. On the other hand, the social Note that supernodes in KaZaa are self-elect- network approach can use a complicated reputa- ed from ordinary peers and may not be fully tion model, and is robust to a wide range of trustworthy. One approach uses predeployed malicious actions. But the probabilistic model proxies instead of supernodes for reputation can be applied to only simple reputation models maintenance [5]. In this approach each peer is (due to the difficulty in probabilistic estimation) attached to a unique proxy according to its IP and is effective against only a few kinds of mali- address. Correspondingly, each proxy is respon- cious actions. The performance of the two mod- sible for a certain IP range, and proxies are els has been compared in [11]. It has been shown organized into a binary search tree based on the that the probabilistic model performs better for IP ranges they maintain. Each peer periodically small malicious populations, while the social net- generates reports about its streaming neighbors. work approach is better when most peers are All reports about a peer are sent to its attached malicious. proxy. A query about a peer’s reputation is also forwarded to and answered by the peer’s GAME-THEORETIC MODEL attached proxy. Figure 1 shows the report sub- Different from the above two approaches, the mission process in this approach [5]. Each circle game-theoretic model assumes that peers have in the figure is a streaming peer, and each quad- rational behavior and uses game theory to build rangle is a deployed proxy. Numbers in a quad- a reputation system. Rational behavior implies rangle indicate the IP range maintained by the that there is an underlying economic model in proxy (here numerical values are used to repre- which utilities are associated with various choic- sent IP addresses). Suppose that streaming peer es of peers and that peers act so as to maximize B is streaming peer A’s child in the streaming their utilities. Fudenberg et al. present a game- overlay, and B prepares to submit a report about theoretic framework to offer certain characteri- A’s performance. If B has not sent any report zations of the equilibria payoffs in the presence about A before, B first sends A’s IP address to a of reputation effects [12]. But the work assumes random proxy (which is R in the figure). R then that a central trusted authority does feedback searches in the tree to identify the proxy whose aggregation, which may not be scalable to large- range covers A’s IP address (T in this case). T scale P2P networks. then sends a response message to B as well as its certificate of trustworthiness (issued by a trusted EPUTATION UERY certification authority). After B verifies the trust- R Q worthiness of T, it sends its report about A to T. In this section we discuss techniques for reputa- In the following, B will directly send reports tion query in P2P networks. about A to T.

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Two important issues in partially centralized used to address this. That is, a DHT network approaches are efficient search and load balanc- can be configured to have multiple replicas As compared to cen- ing among multiple supernodes/proxies. First, responsible for the same key, or multiple hash each peer should be attached to a unique super- functions can be used to map each peer to multi- tralized approaches, node or proxy. In MD, this is done by KaZaa’s ple reputation managers [6]. When a peer partially centralized built-in mechanism. If a P2P network does not searches for the reputation of another peer, it approaches have have such a built-in mechanism, this is not easy. finds all the replicas responsible for the key and Suppose each proxy is responsible for a certain uses a voting scheme to compute the final result. significantly range of peers. Given any peer in the system, we However, voting cannot guarantee obtaining the improved system need to quickly identify the proxy responsible for correct decision and does not completely address it (e.g., for reputation update or query). If the the problem. As shown in [11], simple collusion scalability. However, number of proxies is small, simple flooding can can seriously affect the result of voting. Second, in order to serve a be used for search. Otherwise, a more complicat- a reputation report or query is delivered between large P2P network, ed overlay structure should be built among prox- its generator and the reputation manager by ies (e.g., the binary search tree in [5]). Second, DHT routing. A malicious peer in the delivery a large number of loads for reputation management should be path may modify, intercept, or discard the report supernodes or evenly distributed among supernodes/proxies. or query. PeerTrust has proposed to encrypt MDA does not consider this issue as it uses the messages in order to prevent data modification proxies may be KaZaa built-in mechanism to attach peers to during delivery [6]. But it cannot prevent data needed, which leads supernodes. In [5] a dynamic load redistribution discarding during routing. In summary, DHT- to high implementa- method has been proposed to balance loads based approaches cannot guarantee secure repu- among proxies. tation computing and delivery. tion and mainte- Compared to centralized approaches, partial- Furthermore, DHT has its own limitations. nance costs. ly centralized approaches have significantly Since peers are highly dynamic in P2P networks, improved system scalability. However, in order a reputation manager may unexpectedly leave to serve a large P2P network, a large number of the system. Then the data maintained by it are supernodes or proxies may be needed, which no longer available. In addition, load balancing leads to high implementation and maintenance mechanisms that abide by DHT storage and costs. routing methods are complicated, especially in dynamic networks. DHT also has its own securi- STRUCTURED OVERLAY ty threats and vulnerabilities, and there are many Another class of approaches uses distributed targeted attacks on its routing scheme, data hash table (DHT) to store and search for peer placement scheme, IP mapping scheme, and so reputation. In DHT each peer is assigned a on. unique peer ID, and each object is hashed to a key in the same space of peer IDs. The peer UNSTRUCTURED OVERLAY with ID equal to the hashed key is responsible XREP uses a polling algorithm to choose reli- for storing the location of the object (or the able resource in Gnutella-like file sharing net- object itself). With a hashed key of an object, a works [14]. It consists of four operations: query for the object is routed through peers in resource searching, vote polling, vote evaluation DHT to the peer that is responsible for the and resource downloading (Fig. 2). The first object. Each peer in DHT maintains a routing operation is similar to searching in Gnutella. A table for routing messages. peer broadcasts to all its neighbors a Query We take PeerTrust as an example [6]. It message containing the search keywords. When adopts P-Grid as the underlying DHT network. a peer receives a Query message for which it It also uses a system-wide hash function Hash, has a match, it responds with a QueryHit mes- which maps one peer ID to another. Suppose sage, as shown in Fig. 2a. In the next operation, that peer p has an ID, ID(p). Whenever p has a upon receiving QueryHit messages, the query transaction with another peer, q, p generates a initiator selects the best matching resource report about q and sends it to the peer with ID among all possible choices. It then polls other Hash(ID(q)) through DHT routing. The repu- peers using an encrypted Poll message to tation of q is then stored and maintained at the enquire about their opinion of the selected peer with ID Hash(ID(q)), which is called the resource or the resource provider. In XREP reputation manager of q. Queries of a peer’s each peer maintains information on its own reputation are also forwarded to its reputation experience with the resource and other peers. manager through DHT routing. In this way, peer Upon receiving a Poll message, each peer reputation is distributedly stored in the system. checks its experience data. If there is any infor- This approach has several advantages. First, mation about the resource or the provider indi- peer reputation is distributedly stored and com- cated by the Poll message, the peer sends its puted at the reputation managers. There is no vote to the polling peer with an encrypted need for a central server or supernodes. Second, PollReply message, as shown in Fig. 2b. a peer’s reputation manager is determined by a In the third operation the polling peer col- universal hash function, which cannot be select- lects a set of votes and evaluates the votes. It ed by the peer itself. This reduces the possibility first decrypts the votes and discards corrupt of collusion between a peer and its reputation ones. Then it analyzes voters’ IPs and detects manager. cliques of dummy or controlled votes. After that, However, this approach has some security it randomly selects a set of votes and directly concerns. First, reputation managers may misbe- contacts the voters with a TrustVote message. have by providing false or random data when Each contacted voter is required to send a answering a query. Majority voting has been VoteReply message for vote confirmation. This

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B B B B

Query Poll TrustVote A QueryHit C A PollReply C A C A C Query Poll VoteReplyTrustVote Download QueryHit PollReply VoteReply Query Poll QueryHit PollReply D D D D

(a) (b) (c) (d)

Figure 2. Operations in XREP: a) resource searching; b) vote polling; c) vote evaluation; d) resource downloading.

forces attackers to pay the cost of using real IPs ized approach has better scalability than the cen- as false witnesses. After this checking process, tralized one, but still relies on predeployed prox- the polling peer can obtain the reputation of the ies or supernodes and is not fully scalable. The resource or provider. Based on the reputation approach based on unstructured overlays does value, the polling peer can either download the not need any central component; however, it is resource, as shown in Fig. 2d, or discard the not as scalable as the DHT-based one because resource and repeat the voting process on anoth- of its high bandwidth consumption in reputation er resource. search. Approaches based on unstructured overlays The centralized and partially centralized have similar limitations to DHT-based ones. approaches are robust to peer dynamics. In Messages may be intercepted or blocked during these approaches reputation values are stored at transmission, and voting is vulnerable to collu- a server or supernodes, which are often highly sion among peers. Therefore, no secure reputa- stable. In the DHT-based approach the leaving tion computing or delivery can be guaranteed. of a reputation manager will lead to the loss of Furthermore, searching or voting on an unstruc- data stored at it. Fortunately, DHT itself has tured overlay is based on flooding, which incurs some mechanisms to keep high data availability heavy traffic in the network. For example, in under peer churn. In the approach based on XREP Poll messages are broadcast throughout unstructured overlays there is little protection the network each time a peer needs to find out against data loss due to peer leaving. It may the reputation of a resource or a provider. encounter high data loss in the presence of peer churn. COMPARISONS Regarding security, the centralized and par- We compare the above reputation query tech- tially centralized approaches are the most secure niques in Table 1 and elaborate on the results if assuming the server and supernodes are fully below. trustworthy. In these approaches reports or A centralized approach requires a central queries are directly sent to the server or super- server for reputation storage, and a partially cen- nodes, and there are no third-party peers in tralized approach relies on supernodes or prede- delivery paths. On the contrary, the approaches ployed proxies. On the contrary, approaches based on structured or unstructured overlays based on structured and unstructured overlays cannot guarantee secure reputation computing rely on peers to manage reputation and do not or delivery. In these approaches a reputation require additional facilities. Specifically, in maintainer may be malicious and provide forged DHT-based approaches a peer’s reputation is data, and a delivery path may contain malicious maintained at its reputation manager, which is peers. Although there are many methods for computed by a universal hash function. In improving system security (e.g., encryption/ approaches based on unstructured overlays, decryption or voting), none of them can guaran- peers often locally hold the reputation of their tee 100 percent security. transaction partners. Based on different storage mechanisms, the ONCLUSION approaches have different reputation search C methods. In a centralized approach a reputation In this article we investigate two key issues in query is directly sent to the server. In a partially P2P reputation systems, reputation estimation centralized approach a query is first sent to a and query. We discuss representative examples supernode, which forwards the query to the tar- in the literature and compare them from multi- get supernode. In a DHT-based approach DHT ple aspects. There are many other research routing is used to route queries. In an approach issues in P2P reputation systems, such as based on unstructured overlays, flooding is often anonymity. In many applications, users may only used, which may consume much network band- be willing to participate if a certain amount of width. anonymity is guaranteed. But most existing repu- Among these approaches, the centralized one tation systems have sacrificed anonymity in has the poorest scalability, while the DHT-based order to provide secure underlying protocols, one is the most scalable. The partially central- where each peer holds a unique certificate, and

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Security Adapta- Deployment Reputation Reputation tion to Trustwor- Message Message Approach Scalability requirement storage query peer thiness of modification discarding dynamics reputation in in maintainer transmission transmission

A central Direct server No (no over- No (no over- Centralized The server Low High Full server access lay relay) lay relay)

A set of Search among Partially Supernodes No (no over- No (no over- supernodes supernodes or Medium High Full centralized or proxies lay relay) lay relay) or proxies proxies

Peers No Structured (computed No (addressed No DHT search High Medium Possible overlay by a hash guarantee by function) encryption)

No Peers (e.g., Unstructured No (addressed No transaction Flooding Medium Low Possible overlay guarantee by partners) encryption)

Table 1. Comparisons between various reputation query techniques.

peers use the certificates to authenticate each [14] E. Damiani et al., “A Reputation-Based Approach for other. Other interesting issues may include ana- Choosing Reliable Resources in Peer-to-Peer Networks,” Proc. ACM CCS ‘02, Nov. 2002, pp. 207–16. lyzing security threats and studying reward/pun- ishment mechanisms. BIOGRAPHIES REFERENCES XING JIN [M] ([email protected])______received his B.Eng. degree in computer science and technology from [1] J. Liang et al., “Pollution in P2P File Sharing Systems,” Tsinghua University, Beijing, China, in 2002, and his Ph.D. Proc. IEEE INFOCOM, 2005. degree in computer science and engineering from the [2] S. Marti and H. Garcia-Molina, “Taxonomy of Trust: Cat- Hong Kong University of Science and Technology (HKUST), egorizing P2P Reputation Systems,” Comp. Net., vol. Kowloon, in 2007. He is currently a member of technical 50, no. 4, Mar. 2006, pp. 472–84. staff in the Systems Technology Group at Oracle, Red- [3] S. Ruohomaa, L. Kutvonen, and E. Koutrouli, “Reputa- wood Shores, California. His research interests include tion Management Survey,” Proc. IEEE ARES ‘07, Apr. distributed information storage and retrieval, peer-to-peer 2007, pp. 103–11. technologies, multimedia networking, and Internet topol- [4] L. Mekouar, Y. Iraqi, and R. Boutaba, “Peer-to-Peer’s ogy inference. He is a member of Sigma Xi and the IEEE Most Wanted: Malicious Peers,” Comp. Net., vol. 50, Communications Society Multimedia Communications no. 4, Mar. 2006, pp. 545–62. Technical Committee. [5] X. Jin, Q. Xia, and S.-H. G. Chan, “Building a Monitor- ing Overlay for Peer-to-Peer Streaming,” Proc. IEEE S.-H. GARY CHAN [M] ([email protected])______received his GLOBECOM ‘06, Nov. 2006. B.S.E. degree (Highest Honor) in electrical engineering [6] L. Xiong and L. Liu, “PeerTrust: Supporting Reputation- from Princeton University, New Jersey, in 1993, with cer- based Trust for Peer-to-Peer Electronic Communities,” tificates in applied and computational mathematics, IEEE Trans. Knowledge Data Eng., vol. 16, no. 7, July engineering physics, and engineering and management 2004, pp. 843–57. systems, and his M.S.E. and Ph.D. degrees in electrical [7] S. D. Kamvar, M. T. Schlosser, and H. Garcia-Molina, engineering from Stanford University, California, in 1994 “The EigenTrust Algorithm for Reputation Management and 1999, respectively, with a minor in business adminis- in P2P Networks,” Proc. WWW ‘03, 2003, pp. 640–51. tration. He is currently an associate professor with the [8] R. Sherwood, S. Lee, and B. Bhattacharjee, “Cooperative Department of Computer Science and Engineering, Peer Groups in NICE,” Comp. Net., vol. 50, no. 4, Mar. HKUST, and an adjunct researcher with Microsoft 2006, pp. 523–44. Research Asia, Beijing. His research interests include mul- [9] Z. Despotovic and K. Aberer, “Maximum Likelihood Esti- timedia networking, peer-to-peer technologies and mation of Peers Performance in P2P Networks,” Proc. streaming, and wireless communication networks. He is a P2PEcon ‘04, June 2004. member of Tau Beta Pi, Sigma Xi, and Phi Beta Kappa. [10] L. Mui, M. Mohtashemi, and A. Halberstadt, “A Com- He served as a Vice-Chair of the IEEE Communications putational Model of Trust and Reputation,” Proc. IEEE Society Multimedia Communications Technical Commit- HICSS ‘02, Jan. 2002, pp. 2431–39. tee from 2003 to 2006. He was a Guest Editor for IEEE [11] Z. Despotovic and K. Aberer, “P2P Reputation Man- Communications Magazine, Special Issue on Peer-to-Peer agement: Probabilistic Estimation vs. Social Networks,” Multimedia Streaming (2007), and Springer Multimedia Comp. Net., vol. 50, no. 4, Mar. 2006, pp. 485–500. Tools and Applications, Special Issue on Advances in [12] D. Fudenberg and D. Levine, “Reputation and Equilib- Consumer Communications and Networking (2007). He rium Selection in Games with a Patient Player,” Econo- was Co-Chair of the Multimedia Symposium for IEEE ICC metrica, vol. 57, no. 4, 1989, pp. 759–78. 2007. He was Co-Chair of the workshop on Advances in [13] S. Jun, M. Ahamad, and J. Xu, “Robust Information Peer-to-Peer Multimedia Streaming at ACM Multimedia Dissemination in Uncooperative Environments,” Proc. 2005, and the Multimedia Symposia for IEEE GLOBECOM IEEE ICDCS ‘05, June 2005, pp. 293–302. 2006 and IEEE ICC 2005.

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