One of several articles from America's Network:
americasnetwork.com
G.Lite gets into the starting blocks
Splitterless DSL trial reveals microfilters will be essential.
By Annie Lindstrom
t's been a little more than a year since carriers, computer
manufacturers, chip makers and asymmetric digital subscriber
line (ADSL) equipment manufacturers formed the Universal
ADSL Working Group (UAWG). Since then, an open
industry standard, G.992.2 (a trimmed down version of
ADSL), has been finalized. The group believes the Universal ADSL standard
(UADSL), or G.Lite, which does not require carriers to install a splitter at the
customer premises, will make it easier and more profitable for carriers to meet
the high bandwidth needs of the mass market than full-rate ADSL, which
requires a splitter.
Carriers are not yet offering the pared-down service, which operates at loop
lengths of up to 18 kft. at a downstream speed of 1.5 Mbps and upstream
speed of 512 kbps. Not to worry, though, the service will make its debut
during the second half of the year, according to the UAWG.
Chip makers and equipment suppliers got the "green light" to begin making
G.Lite-compatible equipment when the International Telecommunication Union
(ITU) voted to determine the standard at its October 1998 meeting in Geneva,
Switzerland.
Trials undertaken since that time, led by BellSouth (Atlanta) and GTE Network
Services (Irving, Texas) using prototype equipment, have already reaped a
wealth of interesting information on G.Lite's performance in the field. The most
interesting finding is that most end users will have to install microfilters at the
premises to tune out interference caused by other electronic equipment in their
homes.
This finding is the result of GTE's trial, which involved telecommuters from Intel
Corp. (Santa Clara, Calif.) using modems supplied by Orckit Communications
Ltd. (Folsom, Calif.) and DSL access multiplexers supplied by Fujitsu
Network Communications Inc. (Richardson, Texas).
The trial, which took place in Hillsboro, Ore., began in September 1998 and
was completed in December. It involved 47 homes located between 4.2 to
17.5 kft. from the central office (CO). According to a report released by the
G.Lite Trial Team, G.Lite successfully delivered top data rates of 1.5 kbps
downstream and 440 kbps to 512 kbps upstream to homes approximately 15
kft. from the CO. However, upstream rates decreased as loop reach
increased, but downstream rates remained very close to 1.5 Mbps.
Trial participants in 81% of the homes involved had to deploy at least one
microfilter on their lines to achieve those rates; 50% had to install more than
one microfilter (up to five). Luckily, the microfilters were effective in solving "a
number of interference problems in both the on-hook and off-hook states of
telephones, fax machines, analog modems and other customer premises
equipment (CPE)," the report says.
The team also found that most homes had at least one phone that required an
off-hook power cutback level of 20 dB upstream in order to avoid ADSL
interference into the telephone. Because that kind of power cutback did not
enable the UADSL modem to reestablish a connection after the off-hook event
occurred, the team left those houses with a power cutback of 10 dB or less
and put microfilters in the offending telephones to solve the problem.
Microfilters were used in 11 of the 47 homes to assist when CPE in its
on-hook state degraded ADSL performance. In addition to increasing down
and upstream data rates, microfilters were used to eliminate errored-second
alarms that occurred despite sufficiently high noise margins, the report says.
And the trial also revealed that CPE was more of a problem for the service
than in-home wiring was.
It's do-able
In Phase One of the trial, the team hooked up 20 of the homes to make sure
the equipment was working properly. In Phase Two of the trial, the team let the
residents of 30 homes install their premises equipment themselves, according to
Tim Novak, manager of product management for Fujitsu. The team videotaped
some of the end users in the process of setting up their service for later analysis,
he notes.
"The bottom line was that 70% were able to do it themselves," Novak says.
Problems encountered with the 30% who were unable to get the service up
and running on their own included bad in-home wiring, including one man who
used speaker wire to connect a phone in his garage to his home wiring; inability
to understand the microfilters; and those who simply did not follow directions,
Novak adds.
G.Lite's impending arrival was heralded at the recent ComNet '99 trade show
in Washington, D.C., with a live demonstration of Efficient Networks Inc.'s
(Dallas) splitterless version of its SpeedStream 4020 universal serial bus (USB)
DSL modem. USB-compatible equipment will make it unnecessary for end
users to open up their USB-equipped computers to install a high-speed
network interface card in their computers in order to use ADSL.
Also at ComNet, Diamond Lane Communications (Petaluma, Calif.)
demonstrated interoperability between its Speedlink systems' G.Lite-based line
card and a Compaq Presario 5110 PC equipped with its 1.5 Mbps Max digital
modem, which uses Lucent Technology Inc.'s (Murray Hill, N.J.)
G.Lite-compliant WildWire DSP 1690 chipset.
In full-rate related news, Alcatel (Richardson, Texas) announced that it has
integrated its discrete multitone (DMT) DSL chipset into its Litespan digital
loop carrier (DLC). The line card will be available midyear, says Jay Fausch,
senior director of marketing and business development for Alcatel. |
