G.Lite gets backing from ITU: Universal ADSL moves one step closer to standardization

Pushed forward by the Universal ADSL Working Group, the International Telecommunication Union has sanctioned the proposed G.Lite standard, known also as "splitterless" asymmetrical digital subscriber line.

The first major hurdle of G.Lite acceptance is the ITU's determination, or final approval, of the technical specification, after which no technical changes to the specification are allowed, said John Cahill, co-chair of UAWG and executive director of the advanced network division at BellSouth.

"The determination aspect is the green-light signal to manufacturers to start to build production-quality releasable equipment," he said. The specification is now available. Formal ratification of the G.Lite standard is expected at the June 1999 ITU meeting.

G.Lite is based on the same standard as full-rate ADSL, so the two technologies will be compatible. Customers can upgrade to full-rate ADSL as their needs and applications evolve. G.Lite supports discrete multitone (DMT), not carrierless amplitude/phase modulation (CAP), and specifies 1.5 Mb/s downstream and 256 kb/s upstream. The specification also includes details for an optional in-line filter.

As vendors rally around the G.Lite standard, Cahill predicts that CAP-based solutions will eventually fall by the wayside. Although vendors and carriers might have to support both technologies during the transition, DMT will prevail, he said.

Larry Yokell, director of product development for megabit services at U S West !nterprise Networking, is more hesitant. U S West has extensive DSL deployment efforts, all of which are based on NetSpeed (now Cisco Systems) CAP solutions. U S West is exploring G.Lite options with Cisco, he said.

U S West would need a strong business case to eliminate CAP. "It's non-trivial to take that technology and switch to DMT," Yokell said. He added that U S West "is participating in the G.Lite concept" of moving away from a customer premises equipment model toward a retail modem model for deployment. In fact, Dell and other vendors are supporting U S West's CAP technology in PCs for the mass market.

Although the primary push for G.Lite will be in the consumer mass market, it won't usurp other DSL technologies. Full-rate ADSL and symmetrical DSL, for example, will maintain market share in the business arena, Cahill said. In fact, G.Lite might be the impetus for full-rate ADSL in the future.

On the heels of the ITU's initial acceptance, vendors announced G.Lite interoperability and deployment trials. PairGain Technologies said its Avidia System and Megabit Modems are already equipped with chips that support full-rate ADSL and G.Lite ADSL.

Also, Fujitsu Network Communications, GTE, Intel and Orckit Communications are testing G.Lite in the Portland, Ore., area. In the trial's first phase, the group turned up G.Lite service in the homes of 20 Intel employees, said Bill McDonald, senior manager of the partner product implementation group at Fujitsu.

"It is a small group of subscribers," he acknowledged. "It's a feasibility study [where we] look at how G.Lite works in a real environment. In Phase 2, we'll expand that trial to 50 subscribers."

Phase 2 is scheduled to start in December.

The trial is proving the validity of the technology, McDonald said. "We have achieved full G.Lite speeds-between 440 to 256 kb/s upstream and 1.5 Mb/s downstream. And those G.Lite speeds have been achieved on loops up to 15,000 feet."

The optional filter is being used in most homes, he added. "At least one microfilter is required in nine of 10 houses, and in three of 10 houses, [users] had to install multiple microfilters," he said. The UAWG is uncertain about whether the microfilters are required, he said. "Some members were insisting they would be, and we did indeed confirm that."

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