Last week, PC Week took a look at some of the issues surrounding the use of broadband and narrowband technologies. One of the technologies mentioned was ADSL (Asynchronous Digital Subscriber Loop) - which seems to be something of a mystery to many net.news readers. With that in mind, PC Week asked Mike Valiant, product marketing manager for US Robotics, to shed some light on the technology.
As the services on offer to subscribers to the Internet become richer, including streaming audio and video feeds, for example, the bandwidth required to deliver them will become much greater than that which is available today. Although the recent development of 56Kbps modem technology offers higher speed access, the theoretical limit for analogue communications has almost been reached.
The answer to PSTN congestion, user frustration and multi-media applications is broadband access, which goes far beyond the speeds offered by ISDN.
Cable providers already supply cable modems with megabit performance.
However, shared bandwidth means that high end-to-end speeds are not guaranteed.
Cable and telecommunications companies are therefore looking at a new technology - ADSL.
As a telecoms model, Digital Subscriber Line (DSL) is already being used to provide ISDN access. ADSL is the preferred next generation access technology to the home because it can use the existing copper pairs which support today's telephone service. Although the technology will require new exchange equipment and migration to Frame Relay and ATM backbones, no additional underground services will be necessary.
Because end-user applications are often asymmetric, ADSL is the ideal solution. Like 56Kbps technology, ADSL provides higher bandwidth towards the subscriber. Depending how far you are from the telephone exchange, downstream speeds range from 1.544Mbps to 8.448Mbps. Upstream, speeds range from 16 to 640Kbps. To put this in perspective, MPEG movies with simulated VCR controls require between 1.5 and 3.0Mbps downstream but no more than 16 or 64Kbps upstream.
During 1997, the first wave of ADSL modems will be rolled out for extensive field trials with telecommunications carriers and cable companies. In common with current analogue modems, they will feature a hybrid, upgradeable approach. This enables DSL modems to support different ways of achieving higher speeds, including CAP (Carrierless Amplitude and Phase) and DMT (Discrete MultiTone), as well as analogue/telephony services in one unit.
At the server end of things, managed remote access solutions will become Digital Subscriber Line Access Multiplexer (DSLAM) access nodes, offering solutions for access, switching, routing and network management. Interfaces for telecoms data backbone switches will be provided, including Frame Relay and ATM. High-speed LAN/WAN connectivity will also be supported.
Potential ADSL users are getting very excited. The technology is being driven by demands from ISPs and content providers. Major telecoms carriers are also enthusiastic, seeing ADSL as a trump card when competing with cable operators, and it's expected that the technology to move forward very quickly throughout Europe.
Individual subscribers and ISPs, though, cannot afford to write off existing investments in conventional dial-up technology. As the next generation solution for remote broadband access, ADSL is what the telecoms industry has been waiting for.
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