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Technical Paper TELECOMMUNICATION STANDARDIZATION SECTOR (12/2011) of ITU International Telecommunication Union ITU-T Technical paper TELECOMMUNICATION STANDARDIZATION SECTOR (12/2011) OF ITU SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Wireline broadband access networks and home networking Foreword Malcolm Johnson Director ITU Telecommunication Standardization Sector This new Technical paper gives a valuable overview of the technologies forming modern access networks, based primarily on ITU-T access network and home networking standards (“ITU-T Recommendations”). The Technical paper’s overall aim is to provide a non-expert reader with the background information necessary to an understanding of the context and content of these ITU-T Recommendations; offering practical guidance to administrations, operators and suppliers in planning and implementing the access networks of fundamental importance to our modern world. Access network technology is advancing rapidly with close to six hundred million subscribers possessing broadband connections to the Internet1. Many of them connect using ITU standardized technologies covering for example; digital subscriber line (DSL) technology, cable modems, or fibre to the home (FTTH). Fixed broadband services are delivered in a variety of ways: over direct optical fibre connections, traditional telephone networks, coaxial cable in community access television (CATV) networks, wireless networks, or even via electricity distribution grids. A broadband connection delivers data, voice and video at unprecedented speeds, with vectored VDSL2 (Recommendation ITU-T G.993.5) achieving aggregate bit-rates in the region of 250 Mb/s, and the “G.fast for FTTdp (Fibre-to-the-Distribution Point)” standardization project, to be completed by March 2014, will increase these rates to an extraordinary 1 Gb/s. The networks enabling such high-speed data exchange are considered critical to spurring economic growth and bridging the digital divide. Today’s access networks have created new opportunities to produce equipment with advanced computational and communications capabilities and to connect this equipment within a home network to the outside world via the customer’s broadband service. In summary, the access network is experiencing rapid technological change, unprecedented subscriber growth rates, a proliferation of new products and solutions, and entries to the market by a wide range of new service providers; resulting in equipment suppliers often unfamiliar with critical standards, and governments eager, but ill-equipped, to deploy these advanced technologies. Access network standardization will consequently see increased involvement from stakeholders not traditionally affiliated with ITU or even the ICT industry. More than ever before, the market for access technologies and networks is in need of coordinated international standardization and we are proud of the leading role ITU-T has earned in this respect. ITU-T Study Group 15 is the global leader in the standardization of transport elements of access networks and home networking. Participation in ITU’s standardization activities is open to all, and I invite experts in this field to join us in our mission to advance the modern communications networks upon which we all depend. 1 http://www.itu.int/ITU-D/ict/statistics/material/pdf/2011%20Statistical%20highlights_June_2012.pdf ITU-T SG15 Technical paper (12/2011) i Wireline broadband access networks and home networking Acknowledgements This Technical paper was prepared under the leadership of Mr Yoichi Maeda, Chairman of ITU-T Study Group 15, and of Mr Tom Starr, Chairman of ITU-T Working Party 1/15. It is based on the contribution of numerous authors who either contributed to the generation of the relevant ITU-T Recommendations or participated in the ITU-T Study Group meetings. In particular, credit for organizing the collection of material should be given to Gastone Bonaventura (Chief Editor) and for the preparation of the text to the following Editors: John Jay (Preface); Miguel Peeters, Massimo Sorbara and Frank Van der Putten (Chapter 1); Fabrice Bougart, Frank J. Effenberger, Richard Goodson, Dave Hood, Makoto Kadowaki, Denis A. Khotimsky, Wei Lin, Yuanqiu Luo, Joe Smith and James Zhang (Chapter 2); Les Brown, John Egan, Stefano Galli, Erez Ben-Tovim and Tetsuya Yokotani (Chapter 3); Gastone Bonaventura (Chapter 4); and the ITU-TSB staff who have contributed to finalize the text. ITU 2013 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ii ITU-T SG15 Technical paper (12/2011) Wireline broadband access networks and home networking Preface Editor: John Jay Development of the PSTN Following the invention of the telephone at the end of the 19th century, a wireline access network was rapidly constructed to provide commercial telephone service. Figure P-1 presents the USA as an example; the number of telephone lines grew by a factor of 60,000 in the first one hundred years after Alexander Graham Bell was awarded a US patent for "Improvement in Telegraphy”. The annual growth in telephone lines in the USA did not fall below 10% until 1908. Figure P-1 – Telephone line growth in the USA from 1880 – 1980 The original design was derivative of the existing telegraph network with technical changes necessary to meet the additional requirements of consumer voice service, including safety, human factors, etc. One of the first adaptations from telegraph networks was the use of twisted wire pair (TWP) for the physical network instead of single wires to protect calls from cross-talk and electrical noise. Telephones were originally deployed in connected pairs, however telegraph exchange technology was quickly applied to the nascent telephone service, and the Public Switched Telephone Network (PSTN), the first wireline subscriber access network, was born. Challenges to the PSTN For most of the 20th century, the PSTN changed little and served its purpose well. Technical advances enabled direct subscriber connections (i.e., dialling) instead of requiring manual connection by an operator, long distance calls using common subscriber equipment instead of dedicated equipment at the telephone company’s facility and eventually direct dialling long distance ITU-T SG15 Technical paper (12/2011) iii Preface and even overseas calls. However in the last decades of the 20th century, technical, commercial and cultural changes began to move the PSTN as it existed to obsolescence. Digital Telephony – Digital signalling and communications techniques were first applied to the PSTN after World War II. Digital conversion increased rapidly through the 1960’s & 1970’s. The technology was developed and implemented to be compatible with the existing PSTN. However it enabled techniques and applications which catalysed many competitive products and services. Digital Data Communications – The development of digital telephony made the PSTN a convenient platform for digital communications between non-telephony devices such as computers. This work initiated in the late 1950’s and of course continues today. In the 1980’s, as consumers began to purchase computers for their homes, their existing access to the PSTN was a natural means of putting their home devices on a digital communications network. The growth in digital data communications over the PSTN can be understood by viewing the increase in consumer modem transmission speeds over time in Figure P-2. Figure P-2 – Telephone line digital modem speed by year Video/CATV – As television (TV) proliferated in the 1950’s, most subscribers received their video signals “over-the-air”, i.e., using a Radio Frequency (RF) antenna to harvest broadcast signals. However in rural or mountainous areas, common home antennae were not adequate to receive over- the-air TV signals. Formal and informal collective arrangements were made to purchase, install and share a “Community Antenna” (CATV) and distribute the received broadcast television signal by a terrestrial wireline network, typically coaxial cable carrying native RF signals. The CATV signal (i.e., picture) quality was better than over-the-air and programming was less restrictive. Thus CATV subscriptions increased through the end of the century until, in places like the US, more than 90 % of all homes can be connected to a CATV system. Digital telephony increased the bandwidth and flexibility of the PSTN, opening it up for complementary and competitive providers, products and services, enabling alien products and protocols to be attached and connected without affecting the service or reliability of Plain Old Telephone Service (POTS). Digital data communications created a whole new industry, connecting computers, devices and more importantly, consumers with information, products and services, i.e., the Internet and the World Wide Web. The emergence and growth of video financed the construction of national CATV networks which became the first direct competitor to the PSTN. These events set the stage for the next generation of the PSTN, the Wireline Broadband Network. iv ITU-T SG15 Technical paper (12/2011) Wireline broadband access networks and home networking The Wireline Broadband Network – ISDN Integrated Services Digital Network (ISDN) was the first attempt at a completely digital telephone/telecommunications network (as opposed to using modems over switched analogue circuits). ISDN provides one or two 64 kb/s digital service channels and a 16 kb/s digital signal channel to each subscriber. It was designed to carry voice,
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