DSL's future still murky
DMT gets a boost, but is underlying technology still the crucial issue?
WAYNE CARTER and KATHLEEN CHOLEWKA
Digital subscriber line is clearly a hot technology, but issues including the split between carrierless amplitude/phase modulation and discrete multitone protocols have clouded its future.
Texas Instruments' acquisition of Amati Communications may have provided a degree of clarification, but the DSL market picture is still developing.
DMT and CAP are line-encoding technologies that maximize copper's bandwidth for transporting data. DMT has won over standards bodies--including the International Telecommunication Union--for asymmetrical DSL, but CAP isn't dead.
Rupert Baines, ADSL product manager for chip-maker Analog Devices, said DMT is the choice for ADSL, but CAP may prevail in other varieties.
CAP is cheaper to implement and requires less power. But DMT produces fewer errors resulting from crosstalk within carriers' copper bundles.
Experts say DMT vendors will develop products that require less power and that CAP will probably flourish in quieter private networks.
Some equipment vendors have aligned strictly with one protocol or the other, and other companies already use both or are open to either.
"We're going to wait to see what happens," says Ian Eslick, founder of Silicon Spice, a California-based chipset vendor and member of the ADSL Forum.
TI is DMT-exclusive, and its acquisition of Amati boosts DMT. But a spokeswoman for TI said that if CAP achieves standard status, TI is open to developing CAP-based digital signal processors (DSPs). And new TI strategic partner Westell Technologies, whose buyout contract Amati terminated when TI came calling, is a CAP stalwart looking to add DMT to its product portfolio.
The TI spokeswoman also pointed out that the programmability of DSPs makes adopting CAP a fairly simple process.
Armando Geday, chief executive of CAP king GlobeSpan Technologies, said the DMT/CAP "technology wars" are over.
"It really doesn't matter what the technology is if the modems work," Geday said.
Regardless of equipment vendors' readiness, the telcos must drive the market, and they've got more important issues than chipsets to deal with, including evaluating which copper lines can carry DSL.
To circumvent substandard copper, service providers like U S West and GTE have deployed ADSL in private multitenant environments or select geographic regions with direct CO connections or few interruptions with DLC equipment.
David Cooperstein, telecom strategies analyst at Forrester Research, is bearish on ADSL.
"I don't think the market exists yet, except for the fact that it gives the [Bell companies] a way to compete with cable modems," he said. "Service providers are deploying to be in the game, not because it's the way of the future for them."
Westell President J. Nelson disagreed.
"The [Bell companies] have to jump in and get both feet wet," he said. "It's the best ammunition they have against cable modems."
But even if that's true and the CAP/DMT issue is dead, the proliferation of DSL varieties may hamstring the technology.
"The question is whether we're moving farther away from a standard with IDSL--and recently CDSL--rather than converging on one," says Dataquest analyst Lisa Pelgrim. "There are a lot of options out there. We still have to wait to see what the market needs." |
