Key DSL flavor faces big compatibility test

Everyone knows that the umpteen flavors of digital subscriber line technology have trouble talking to each other. But did you know that G.Lite - considered the DSL flavor most likely to succeed - still can't talk to itself?

G.Lite modems will have compatibility problems until a standard is firmly set. Then, equipment vendors can focus on interoperability.

Modem makers are feverishly trying to correct compatibility problems so customers can buy any G.Lite modem and sign up for any G.Lite service without worrying about which company's modem is at the other end of the connection.

Vendors hope to solve the bulk of the problems in time for a crucial compatibility test this summer - the G.Lite Inter-operability Showcase, scheduled for June at the SuperCom trade show in Atlanta.

But some vendors say they will not participate in the event. They worry that even if current modems succeed in communicating with each other, the gear still may not be able to swap data at a full 1.5M bit/sec download speed and may lack management features carriers need to offer DSL services.

DSL vendor Paradyne will skip the demonstration because it won't be worth the frantic effort, says Frank Wiener, vice president and general manager of Paradyne's DSL division. The final G.Lite standard won't be approved until after the show.

Whatever interoperability is demonstrated may be rudimentary and slower than top speed. "Throughput will be the question," Wiener says.

Part of the compatibility problem is that with the standard still developing, vendors building products now are trying to hit moving targets, including DSL chip makers. If the chips don't work with each other, neither will the modems built around them, as modem maker 3Com has already discovered.

3Com builds DSL customer modems using chips from Alcatel, Analog Devices and Texas Instruments. As those vendors tinker with the software that runs the chips, 3Com doesn't have the staff to keep revising the modem software that rides on top, says Al Brisard, 3Com's director of marketing and business development. Chip makers need to stabilize their products, he says.

Alcatel and Analog Devices are working on the problem and plan for their chips to be interoperable by June, says Stephen Makgill, director of asymmetric DSL product management for Alcatel. At that point, modem makers will be able to focus on making the modems compatible, Brisard says.

While rushing the compatibility effort may drive modem makers a little crazy, service providers can't wait for them to succeed.

When they do, customers will be able to buy modems in retail stores. Service providers won't have to be in charge of modems at the customer end of the connections as they are today. Service providers will just turn on the service, adding a broadband datastream to the voice channel already on the line.

One carrier says it will hold off deploying a planned DSL service for six months, until the company is sure all the wrinkles are ironed out of G.Lite. "We're willing to wait until the first quarter of next year if it means the modems will be available in retail stores. We don't want to have to troubleshoot why the modem doesn't work with the [carrier DSL modem]," says Rich Poland, a network engineer for Blair Tele-phone Company in Blair, Neb.

G.Lite has been on a fast track since January 1998, when a group, including Microsoft, Intel, Compaq and the regional Bell operating companies, decided it wanted G.Lite standardized as soon as possible.

That group, which is known as the Universal ADSL Working Group (UAWG), is organizing the interoperability showcase and exerting pressure on modem makers. The group wants a demonstration of widespread G.Lite interoperability.

Features that go beyond passing data may not be ready for the showcase, according to Ken Krechmer, technical editor of Communications Standards Review in Palo Alto, and a member of the ITU G.Lite standard committee.

Those features include a sophisticated handshake between modems, Management Information Bases and a quick way to re-establish disrupted DSL links. The management feature and perhaps other work may be pushed off the plate for the June demonstration, Krechmer says. o

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