Article 40087 of comp.dcom.telecom: Path: mri-gw!psinntp!psinntp!psinntp!rebecca!rpi!gatech!swrinde!cs.utexas.edu!math.ohio-state.edu!news.acns.nwu.edu!news.eecs.nwu.edu!telecom-request Date: Fri, 20 May 1994 13:18:06 +1000 From: zcirrw@minyos.xx.rmit.EDU.AU (Robin Whittle) Newsgroups: comp.dcom.telecom Subject: ADSL and MPEG Viewing Tests Message-ID: Organization: TELECOM Digest Sender: telecom@eecs.nwu.edu Approved: telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 14, Issue 240, Message 1 of 14 Lines: 168 Magazine article on ADSL and MPEG-2 by Robin Whittle ADSL stands for Asymmetrical Digital Subscriber Line - a technology for transferring several Megabits/sec of data to the home, and several hundred kbits/sec back to the exchange, using the existing twisted pair copper wires - while the existing analog phone uses them as usual. It does this by throwing a *lot* of Digital Signal Processing at the many barriers the existing wires present to high bit-rate communications. Each ADSL link is independent - it is not like a shared coax cable. For each link, there must be two transceivers - one at the exchange and one at the home. ADSL is seen as a way of bringing Pay TV, Video On Demand and Interactive Broadband Services to homes without the need to lay new cable. In the May and June editions of {Australian Communications} is a two part article I have spent several months preparing. 16 pages of text, tables and diagrams report on DMT ADSL and on the results of the MPEG Test Group's recent subjective viewing tests. The Test Group reports that for MPEG-2, for some types of program, 5 to 6 Megabits/sec is required to give quality comparable to normal television. This does not include 256 to 400 kbit/sec for sound. 2 Megabits/sec may be OK for film material compressed off-line, where a human operator can fine tune the compression algorithm's attention to the most important part of the picture. Fast action video material is much more demanding. Here is an outline of the two parts of the article. Part 1 - ADSL - Bridging the Superhighway Gap? Introduction. Video On Demand. Provision of alternative phone services. Brief comparison with coaxial cable, satellite and microwave Pay-TV distribution. CAP and DMT - Two Approaches to ADSL. How QAM (Quadrature Amplitude Modulation) works - as in CAP. DMT (Discrete Multi Tone) is 249 channels of QAM. The Twisted Pair Bottleneck. Physical description of buried telephone wires. Barriers to transmission of data :- Attenuation. Inter-Symbol Interference. Interference and Noise. Crosstalk. HDSL - High bit-rate Digital Subscriber Line. Brief mention of this which provides 2 Mega bits/sec duplex over 2 or 3 pairs. Why the ANSI standards committee chose DMT over CAP. Telecom Australia's ADSL Pilot - for 300 homes in early 1995. 71 hour 2 Mega bit/sec Video Server from DEC. 155 Mega bit/sec SDH fibres link to ADSL switches, each with 100 CAP or DMT transceivers. Diagram and discussion of the system - which will be the second or third in the world and the first at 2 Mega bits/sec. Table listing the ANSI draft standard's options for downstream and duplex data rates. Discussion of cost and (dis)advantages compared to digital coax. Part 2 - Bringing Home ADSL - The Race is On Detailed discussion of reach limits - depending on cable and data rates. It seems that 6 Mega bit/sec could work to 3 km of 0.4 mm cable (10 kft of 26 gauge). This - or a little more - may be enough to reach between 80 and 95% of urban subscribers in Australia. Many doubts remain about the distribution of cable lengths, crosstalk, impulse noise and the performance of practical ADSL transceivers. Computer models predict 3.7km for 6 Megabits/sec and way over 4km for 2 Megabits/sec. I expect it will take two years of transceiver development, extensive field trials and new surveys of the existing cables before anyone will really know how many homes can be reached at 6 Megabits/sec. Cost and Availability - Assessment of plans by Amati, Motorola and Aware & Analog Devices. Amati plans to release a 2 Megabit/sec "Presto" and a >6 Megabit/sec "Overture" which will use Motorola DSPs and Amati's own custom chips. Aware & Analog Devices are working on multi DSP "chipset" and will evolve cheaper designs from there. Analog Devices have a low-cost 2 MHz 14 bit monolithic Analog to Digital Converter which will be essential for low cost ADSL transceivers. Motorola are designing a single chip transceiver for 1996 at