Broadbanding together: ATM, ADSL proponents accelerate joint developments

A group of forums and standards bodies is stepping up efforts to refine asynchronous transfer mode over asymmetrical digital subscriber line. The ATM Forum, the Universal ADSL Working Group, T1E1.4 and the ADSL Forum met in conjunction with the ATM Forum's meeting in late July to pursue faster development of the technology.

Continued development of such applications is crucial to the future of ADSL. Those who are working to push ADSL to broad markets believe that PPP over ATM over ADSL is the best way to move high-speed data traffic over copper lines. Although ATM over ADSL is a viable solution today, it must be refined to meet the eventual needs of the market, said Marlis Humphrey, president of Vitreous Communications Inc. and charwoman of the ATM Forum board.

"We don't want to leave the impression that you can't deploy ATM over ADSL today," Humphrey said. "This [joint effort] will lead to the most efficient [solution] for multimedia, multiservice, large-scale networks."

ATM over ADSL is used primarily for fast Internet access, but the groups' efforts to refine it will allow a full range of services to be deployed over existing copper lines, Humphrey said.

ATM is growing out of its transport-only role, according to Tim Kwok, UAWG technical chairman and broadband architecture manager for Microsoft. "ATM is becoming very important in the public network space for connecting customers," he said. "ATM is the key enabling technology for broadband."

Microsoft included ATM support in Windows 98 for that reason, Kwok said, and the company sees ATM growing in importance for the industry. "Using PPPover ATM makes the ISP point of presence easier to deploy," he said. "One ATM pi pe can support multiple virtual circuits."

The July ATM Forum meeting was focused on pressing forward in some key areas, said Tom Star, a senior member of Ameritech's technological staff and chairman of T1E1.4.

"The industry has pretty well dealt with [Internet protocol] or PPP over ATM," he said. "This meeting was about taking the next step."

One of those steps is adapting ATM to G.lite, the splitterless standard being developed for residential markets. The technology will allow customers to receive incoming phone calls while on-line, but the system will respond to the off-hook signal by dropping the bit rate to let the incoming call through. When the call is terminated, it reallocates that bandwidth to the data call.

"ATM is classically designed to work over more benign transmission channels," Star said. "ATM quality of service works by ensuring bit rates, delay, peak rates and sustained rates. G.lite changes the parameters negotiated for the virtual circuit."

It's difficult to identify one issue over the others as most important, but dealing with rate changes and interruptions is perhaps a bit higher in significance, said said Mark Teden, UAWG marketing chairman. The solution appears to be a so-called fast retrain, which means speeding up the process that the G.lite signal uses to retrain to a different rate. That would keep the higher levels of ATM from getting a lost signal indicator and terminating the data call. Teden said that such a solution is near.

Humphrey said it has become clear that ADSL, particularly G.lite, is the largest market opportunity for ATM to date. And because ATM may help trigger the explosive growth that ADSL vendors and service providers are hoping for, ADSL and ATM supporters are gaining momentum in developing better solutions.

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