$10 microfilters pose threat to G.Lite
By Will Wade and Loring Wirbel
EE Times
(11/12/99, 3:47 p.m. EDT)
DALLAS — An inexpensive passive component could swing open the
door to full-rate asymmetric digital subscriber line connections and
allow carriers and users to bypass a slower ADSL version for which
many companies only recently have marshaled silicon support.
The $10 microfilter in question could shake up the market for G.Lite, a
1.5-Mbit/second version of ADSL that can be installed in homes
without requiring an external splitter to separate voice and data traffic.
Full-rate ADSL pumps data through the same copper telephone cable
as voice signals at rates up to 8 Mbits/s but requires a splitter, which
must be installed by the user's local phone company. G.Lite removes
external splitters from homes by using a discrete-multitone (DMT)
subset, reducing the maximum downstream capacity of ADSL.
But after the first G.Lite chips hit the market, tests by a team led by
John Cioffi at Stanford University revealed that the splitterless systems
could see severely eroded data speeds when nearby phones were taken
off the hook, and users heard significant noise when trying to place a
voice call. As a tactical response, Texas Instruments Inc. and
Globespan Inc. designed microfilters — tiny devices that plug into every
phone or fax in the home to demarcate voice and data traffic and keep
the signals clean — to sell along with their chip sets. 2Wire Inc.
(Milpitas, Calif.), whose main business is residential gateways for
broadband consumers, developed its own microfilters to drive the total
market for its core business, and it has outsourced production to
passives manufacturers.
Ironically, the solution intended to fix G.Lite from a technical
perspective has harmed it on the marketing front, since microfilters may
now be used with full-rate modems to eliminate the external splitter.
"The implications are simple: You can have the same reductions in truck
rolls you get with G.Lite, and speeds up to 6 Mbits," said one source at
SBC Communications Inc. "You do the math."
Call it G.Dumb?
While there are still valid reasons to use G.Lite technology in carriers'
central offices, it seems likely that the filters will shake up the market for
home DSL systems. "We say G.Lite should be called G.Dumb," said
Ted Faganson, director of product marketing for 2Wire, which started
shipping microfilters this month for $9.95. They plug into standard
RJ-11 wall jacks.
"Using microfilters means there is no purpose in deploying G.Lite to
homes," he said. "If the line can handle the full 8-Mbit/s speeds and the
modems can handle either speed, why not use regular ADSL?"
Faganson said the future of residential ADSL will be in full-rate chip
sets in the consumer modems and a tier of different rates and speeds
offered by the carriers. Will Strauss, president of market research firm
Forward Concepts (Tempe, Ariz.), agreed.
"Installing microfilters is creating a distributed splitter system in the
home, and that eliminates the advantage of G.Lite," Strauss said. "G.Lite
was originally created to eliminate the need for a service call to install a
splitter. If you can get the same results with microfilters and still don't
need the truck roll, then there's no reason not to use the faster ADSL."
In fact, many ADSL chip vendors have quietly begun shifting their
production to full-rate ADSL versions, and carriers are adopting the
technology for home use. "We're not waiting for G.Lite," Jeff
Waldhuter, director of technology and engineering at Bell Atlantic, said
at the recent DSL Summit conference in Dallas. "We're shipping a
full-rate customer premises solution with in-line filters."
Waldhuter said that using microfilters on every analog phone in the
house brings another advantage: Customers can move their PCs from
room to room, retaining always-on DSL services without worrying
about varying ingress noise levels in different regions of the house.
Untethered from the single location near an RJ-11 jack , customers may
alter their Internet usage patterns to take advantage of the always-on
Web link.
"When you've put what is, in essence, a distributed filter network in the
home, all your assumptions change," said Chee Kwan, director of
broadband products at Conexant Systems Inc. "It doesn't make G.Lite
irrelevant, but it makes the decision to move to sub-rate DMT less
compelling."
Some carriers, chip makers and OEMs remain firm backers of G.Lite.
Service provider Northpoint Communications Inc. (San Francisco) has
finished G.Lite trials in Santa Clara, Calif., and is prepared to launch a
multicity G.Lite offering that involves retail sales through Tandy/Radio
Shack, according to Mark Peden, director of technology strategy.
Peden, former chairman of the Universal ADSL Working Group, the ad
hoc industry group that rallied behind G.Lite, said that any move to
make DSL services cost-effective is a boon to the industry. That would
include full-rate ADSL through microfilters, Peden said, but he believes
G.Lite retains the edge in low power dissipation and interoperability
across vendors.
But others are still pushing G.Lite forward, and "G.Lite is definitely
going to be the accepted medium for consumers," said Kevin McClure,
senior analyst for communications ICs at Dataquest Inc. (San Jose,
Calif.).
Motorola Inc. also backs the splitterless standard for consumer
markets. While G.Lite adoption is proceeding quickly, "not all of the
central office switches have updated software; the new code has not
reached all of the COs, and that has caused some delays," said Matt
Nelson, G.Lite product line marketing manager for Motorola
(Huntsville, Ala.). "But on the consumer side, I think it is important to
note that G.Lite reached a fully interoperable standard well ahead of
full-rate [ADSL], which is about a year behind."
Todd Andreni, ADSL marketing manager for Texas Instruments,
nonetheless said he sees evidence that full-rate ADSL, not G.Lite, will
be the winner for consumer access. TI is supplying DSL silicon for both
the central office and the consumer connection. It is focusing on
client-side silicon that offers full-rate capabilities, while allowing service
providers to retain the ability to scale back the data rate to 1.5 Mbits/s.
"All of the service providers we have talked to are moving toward
splitterless full-rate and not G.Lite," Andreni said, adding that Texas
Instruments itself "is agnostic on the issue."
There is little cost difference between G.Lite and full-rate silicon,
Andreni noted, and for service providers, a single standard may be
preferable; it's "much easier to monitor, because they can serve every
market" with the same infrastructure.
TI's rollouts with OEM customers are focusing on splitterless full-rate
ADSL with G.Lite support, said business development director Terry
Riley.
Yet the rise of the microfilter doesn't completely collapse the G.Lite
chip set market. Faraj Aalaei, vice president of marketing at Centillium
Communications Inc. (Fremont, Calif.), said G.Lite line cards can be a
cost-effective solution for carriers, letting them field full-rate services to
customers able to pay for it, and slower chip sets for users willing to
accept G.Lite's slower data rates.
"G.Lite line cards use much less power than full-rate versions, and the
densities are much higher," Aalaei said. "The whole goal of G.Lite is to
reduce complexity and power dissipation."
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(Pair's Falcon Chip with both G-Lite and full rate ADSL.)
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