one for url-heads: DSL: Can't we all get along? DSL-Lite spec does not ensure interoperability.
nwfusion.com
By TIM GREENE
Network World, 06/14/99
ATLANTA - More than 30
digital subscriber line
(DSL) modem companies
last week demonstrated compatibility
among their products. But that doesn't
mean you can buy the modems and expect
them to work with everyone else's - yet.
Interoperabilty results
The modems on display at last week's
SuperComm '99 show in Atlanta met all
the basic specifications outlined by the
pending standard for DSL-Lite. That DSL
flavor is seen by many as the best hope
for widespread DSL deployment and as a
top challenger to cable modems.
But because of variations in how vendors
implemented the specifications, the
modems could talk to some of the other
modems in the demo, but not to all of
them.
Modem makers and service providers at
SuperComm say they are still on track to
deliver DSL-Lite services and
interoperable equipment late this year or
early next year. But vendors and
providers also acknowledge that they
have to do more to show that the modems
can work over long enough distances and
recover quickly after DSL connections
fail.
DSL-Lite, along with other flavors of the
high-speed access technology, were the
talk of SuperComm '99, a show geared
mainly toward service providers and
their suppliers.
Unlike other DSL flavors, DSL-Lite, also
known was G.Lite, can be used in
modems installed by customers and can
support 1.5M bit/sec downloads. The
modems are suitable for branch- or
home-office connections to corporate
networks via the Internet. The modems
also support a regular voice channel over
the same phone line.
Still, the Universal ADSL Working
Group (UAWG), which organized the
showcase, declared it a success.
"We thought if we could get six vendors
here, this would be a successful event,"
says Mark Peden, the UAWG marketing
committee coordinator.
But others were less enthusiastic because
the tests were done under laboratory, not
real-world, conditions.
"They can test the bejesus out of the
technology, but they'll still have some
problems when it's deployed,"says Mike
Lutz, director of product evaluation for
DSL provider Darwin Networks. "At
least for a while, it's going to be like
analog modems were. There are going to
have interoperability problems, and that
will give the technology a black eye."
"These are not the last tests that will be
needed to assure compatibility," says Ken
Krechmer, editor of the "Communications
Standards Review" and one of the authors
of the DSL-Lite standard.
But Krechmer notes that the showcase
overall drove vendors to hasten
interoperability.
Although the demonstration was held at
SuperComm, the actual testing was
conducted last month at the University of
New Hampshire. During the tests, DSL
modem makers had their equipment pass
data over wire that was 6,000 feet long,
according to participants. Typically,
carriers hope to be able to deploy
DSL-Lite over wires that are 12,000 feet
or longer.
Also, the tests didn't require modems to
perform fast retrain, which involves
re-establishing a link quickly when a DSL
connection is disrupted.
While insisting the demonstration was
successful, the UAWG at the same time
refused to publish the results of the
interoperability tests. The only way to get
the information was to travel from
demonstration station to demonstration
station and write the results down.
Even then, the results were partial.
Vendors said they could demonstrate
more compatibility, but could not get
enough connections at their demonstration
stations to do so.
Peden says that by summer's end, a test
bed group will be appointed to certify
whether DSL-Lite gear is interoperable.
The testing group will be similar to
CableLabs, the cable TV industry group
that developed a standard for cable
modems.
Joining the interoperability parade,
purveyors of highbit-rate DSL2 (HDSL2)
technology - which essentially turns a
regular phone line into a T-1 line- have
established the HDSL2 Interoperability
Consortium.
The group will fund a lab at the
University of New Hampshire where
HDSL2 vendors can test their gear for
compatibility with other vendors'
equipment.
Voice over DSL was also demonstrated
widely at SuperComm, but it comes with
the interoperability problems that all
other flavors of DSL face. Vendors are
starting to address interoperability issues,
but there is no over-riding
interoperability scheme yet.
Also at SuperComm, Adtran introduced
yet another flavor of DSL - multi-bit-rate
DSL (MDSL). This technology is said to
work on phone wires as long as 30,000
feet without a repeater in the middle of
the line to boost the signal.
The speed of the connection drops from
1M bit/sec on a line that is 15,000 feet
long to 144K bit/sec on a 30,000-foot
line. One problem with DSLdeployment
is that some sites are too far from phone
company switching gear for DSL to carry
over the line. Installing repeaters jacks up
the price of service.
G.Lite interoperability results
These are the results of interoperability
tests that were demonstrated at
SuperComm last week.
Each participating vendor of customer
site modems is listed, followed by the
names of vendors whose switching office
modems they could talk to.
Note: Some vendors claimed they could
interoperate with more than they were
actually demonstrating at the show, but
this could not be verified by the group
running the showcase. The Universal
ADSL Working Group would not release
the results of its interoperability tests.
3Com: Alcatel, Cisco, ECI Telecom,
Ericsson, Hyundai, NEC, Newbridge,
Nortel, Pairgain, Samsung, Siemens
Alcatel Access Systems: Alcatel, Cisco,
Ericsson, NEC, Nortel, Siemens
Analog Devices: Alcatel, Ericsson,
Cisco, Hyundai, Newbridge, Samsung,
Siemens
Ascend: ECI Telecom, Hyundai, NEC,
Next Level Communications, Samsung
Cayman Systems: Cixco, Ericsson, NEC,
Next Level Communications, Nortel,
Siemens
Centillium: Centillium, Fujitsu
Cisco: Alcatel, Cisco, ECI Telecom,
Hyundai, NEC, Samsung
Compaq: Alcatel, Cisco, NEC, Nortel,
Samsung, Siemens
Conexant: Hyundai, Pairgain
Efficient Networks: Alcatel, NEC,
Newbridge, Nortel, Siemens
Flowpoint: Alcatel, Cisco, Ericsson,
NEC, Nortel, Siemens
GlobeSpan: Next Level Communications,
Samsung
Hyundai: Cisco, NEC
Intel: Alcatel, Cisco, NEC, Nortel,
Pairgain, Samsung
ITeX: Alcatel, Cisco, NEC, Nortel,
Pairgain, Siemens
Lucent: Alcatel, Cisco, ECI
Telecommunications, Nortel, Samsung,
Siemens
Motorola: Hyundai, NEC, Nortel,
Samsung
Next Level Communications: ECI
Telecom, Next Level Communications
Orkit: Centillium, Fujitsu
Samsung: Cisco, NEC, Nortel
Texas Instruments: Alcatel, Pairgain,
Siemens
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