Networked Surfaces: A Novel LAN Technology James William Scott Churchill College, University of Cambridge September 25, 2002 This dissertation is submitted for the degree of Doctor of Philosophy Abstract Networked Surfaces: A Novel LAN Technology James William Scott Networked Surfaces are a novel technology, which allows physical surfaces such as desks to be augmented in order to provide networking and other services to devices placed on top of them. The devices, which are required to be augmented with special hardware, may include notebook PCs, PDAs, peripherals, and other types of device habitually placed on surfaces. When such a device is placed on a Networked Surface, a handshaking protocol is used to establish a connection between it and the appropriate services. These services may in- clude low-speed and high-speed networking, the provision of power, and also the accurate estimation of the location of the device. The concept of Networked Surfaces raises many issues in networking, which are explored in this thesis in the context of the OSI networking model. At the physical layer, the hardware required to provide connectivity to services is complex, involving a distributed architecture and use of particular conductive pad layouts on the surface and object. The implementation of a fully functional prototype is described. At the link layer, methods for connection and disconnection detection are presented and evaluated. The high speed network used in the prototype is discussed, and includes a novel bus arbitration scheme appropriate to the Networked Surfaces environment. The characteristics of the high speed Networked Surfaces network interface include the possibility of frequent connection and disconnection. This raises issues at the network and transport layers, including those of support for mobility, and of multiple network interfaces. Also discussed are methods of improving the performance of the TCP protocol in these conditions, using a \smart link layer" approach. Finally, the provision and use of location information is presented. The accuracy of this information is found to be comparable with the best current indoor location technolo- gies, with orientation information also provided with a high degree of accuracy. Integration with other systems in the field of \context-aware" computing is described, as well as some applications that Networked Surfaces can enable in this field. iii To my father Tony, my mother Eva, and my brother Mike. Preface Except where noted in the text, this dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration. I hereby declare that this dissertation is not substantially the same as any that I have submitted for a degree or diploma or other qualification at any other University. I further state that no part of my dissertation has already been or is being concurrently submitted for any such degree, diploma or other qualification. This dissertation is comprised of 54,000 words and 63 figures. All trademarks are acknowledged to be the property of their respective owners. James William Scott September 25, 2002 vii Acknowledgements I am indebted to three people for support with this work. Frank Hoffmann, my project partner, taught me much about hardware design, performed a lot of the hardware grudge work in building the Networked Surface prototype, and was a pleasure to work with. Glenford Mapp, my \proxy" supervisor, offered useful advice at every stage, and helped me identify and focus on the most fruitful issues. Andy Hopper, my supervisor, provided me with a clear road towards my PhD, sage advice on research issues, and also helped to locate funding, particularly for my final year. Thank you all. I would also like to thank many people at the Laboratory for Communications Engineering and at AT&T Laboratories Cambridge for support with various stages of this work. In particular, Mike Hazas provided a sounding board for many ideas, as well as pedantically proofreading and insightfully commenting on various draft publications including this work. Ant Rowstron, formerly of the LCE, contributed valuable ideas in the original stages of the project. Also, Robert Harle, Robert Headon, Eli Katsiri, Diego L´opez de Ipina~ and James Weatherall all offered useful comments about interactions between my research and their own work. Finally, I would like to gratefully acknowledge funding from the Schiff Foundation of Cambridge and from AT&T Laboratories Cambridge. ix Publications This dissertation is based in part on work included in the following publications: James Scott and Frank Hoffmann. Networked Surfaces. In Proceedings of Multi-Service Networks 2000, Abingdon, Oxfordshire, England, July 2000.1 James Scott, Frank Hoffmann, Glenford Mapp, Michael D. Addlesee and Andy Hopper. Net- worked Surfaces: A New Concept in Mobile Networking. In Proceedings of the Third IEEE Workshop on Mobile Computing Systems and Applications, Monterey, California, USA, De- cember 2000.2 Frank Hoffmann, James Scott, Michael D. Addlesee, Glenford Mapp, and Andy Hopper. Data Transport on the Networked Surface. In Proceedings of the 26th Annual IEEE Confer- ence on Local Computer Networks, Tampa, Florida, USA, November 2001.2 James Scott, Frank Hoffmann, Glenford Mapp, Michael D. Addlesee and Andy Hopper. Networked Surfaces: A New Concept in Mobile Networking. To appear in ACM Mobile Networks and Applications, 7(5), October 2002.2 Frank Hoffmann and James Scott. Location of Mobile Devices Using Networked Surfaces. To appear in Proceedings of Ubicomp 2002, G¨oteborg, Sweden, September 2002.3 1The first author was awarded the British Computer Society Young Researcher Prize for this presentation. 2The first two authors contributed equally to this work. 3Both authors contributed equally to this work. xi Contents List of Figures xvii List of Tables xix 1 Introduction 1 1.1 Networking Technologies . 1 1.1.1 Wired Networks . 2 1.1.2 Wireless Networks . 2 1.1.3 Networked Surfaces . 2 1.2 Properties of Networked Surfaces . 3 1.2.1 Generic Connectivity . 3 1.2.2 Convenience . 3 1.2.3 Safety . 4 1.2.4 Provision of Location Information . 4 1.2.5 Provision of Power . 4 1.3 Research Overview . 4 1.3.1 Project History . 5 1.3.2 Thesis Outline . 5 2 Design and Implementation of a Networked Surface 7 2.1 Introduction . 7 2.1.1 Design Principles for the Networked Surface . 7 2.1.2 Layout of this Chapter . 8 2.2 System Design . 8 2.2.1 Topology and Handshaking . 8 2.2.2 Functions . 9 2.2.3 Distributed Architecture . 10 2.3 Topology . 11 2.3.1 Requirements of the Topology . 11 2.3.2 Generic and Non-Generic Pads . 12 2.3.3 A Useful Topology . 13 2.3.4 Dimensions of a Useful Topology . 14 2.4 Object Connection and Disconnection . 15 2.4.1 Object Grounding . 15 2.4.2 Handshaking and Registration . 19 2.4.3 Disconnection Detection . 21 xiii xiv CONTENTS 2.5 Surface Buses and Object Types . 23 2.5.1 Networked Surface Bus Requirements . 23 2.5.2 Networked Surface Object Requirements . 24 2.5.3 Object Types . 24 2.5.4 Tile Control Bus . 26 2.6 Prototype Design . 26 2.6.1 Rationale for Prototype Construction . 26 2.6.2 Data Buses . 27 2.7 Prototype Hardware . 29 2.7.1 Tile Controllers . 30 2.7.2 Surface Manager PCI card . 32 2.7.3 LVDS Object . 35 2.7.4 I2C Object . 37 2.8 Prototype Software . 37 2.8.1 Linux Operating System Model . 38 2.8.2 Device Driver . 39 2.8.3 Driver/Daemon Interfaces . 41 2.8.4 User-Level Daemon . 42 2.9 Alternative Designs . 44 2.9.1 Optimisations to the Existing Prototype . 44 2.9.2 Densely Populated Surfaces . 46 2.9.3 Other Physical Media . 47 2.10 Summary . 48 3 Networking with Networked Surfaces 49 3.1 Introduction . 49 3.2 The Handshaking Protocol . 49 3.2.1 Protocol States . 50 3.2.2 Protocol Design and Implementation . 52 3.2.3 Evaluation and Analysis . 57 3.3 The Registration Protocol . 61 3.3.1 Solicitation of Registration . 61 3.3.2 The Registration Process . 62 3.3.3 Dynamic Addressing . 62 3.3.4 Evaluation . 62 3.4 High Speed Bus Interface . 63 3.4.1 Framing Methods . 64 3.4.2 Software/Hardware Interface . 66 3.4.3 Bus Speed Analysis . 68 3.4.4 Low-Level Bus Speed . 69 3.5 Bus Arbitration . 70 3.5.1 Existing Arbitration Schemes . 70 3.5.2 Token Star . 71 3.5.3 Networking Characteristics of Token Star . 73 3.5.4 Disconnection and Reconnection using Token Star . 78 3.6 Summary . 82 CONTENTS xv 4 Networked Surfaces and Other Networks 85 4.1 Introduction . 85 4.2 Comparison of Networked Surfaces and Other Networks . 85 4.2.1 Wired Networks . 85 4.2.2 Wireless Networks . 86 4.2.3 Comparison with Networked Surfaces . 87 4.3 Addressing and Routing with Networked Surfaces . 88 4.3.1 Issues Affecting Addressing on Networked Surfaces . 89 4.3.2 Addressing and Routing Schemes for Networked Surfaces . 91 4.4 Supporting Multiple Network Interfaces . 93 4.4.1 Devices Supporting Multiple Networks . 93 4.4.2 Advantages of Using Multiple Networks . 94 4.4.3 Network-Layer Issues in Using Multiple Networks.