The following highlights xDSL concerns ADDITIONAL to those I mentioned: "Big Questions Still Confront DSL Services"
(04/16/99, 5:26 p.m. ET)
By Loring Wirbel, EE Times
(from techweb.com )
The struggle to get DSL services off the ground
is far from over, based on conversations at
DSLcon in Dallas this pastweek. Divided
standards, questions about interoperability
testing, and glitches in deployment continue to
dog the various flavors of xDSL in both
residential and business markets, casting a
shadow over hopes to quickly drag telephony
into the broadband era.
Despite all the loose ends, the Universal ADSL Working
Group -- the high-profile consortium developing a
splitterless version of DSL -- plans to disband at the June
Supercomm show in Atlanta, declaring victory in its
efforts to define a version of DSL for residential mass
markets. With completion of "Plugfest" tests over the next
month, the UAWG expects to turn test and handshake
"etiquette" issues over to the ADSL Forum.
Developers in both the ADSL and SDSL worlds, as
well as in the high-bit-rate DSL-2 market, are concerned
that no formal neutral interoperability certification lab
exists.
Moreover, the standards process has become fragmented,
particularly in HDSL-2, the emerging standard for a
single-pair symmetric service at T1 speeds. The American
National Standards Institute has taken responsibility for a
single-rate 1.5-megabit-per-second service, while the
International Telecommunication Union (ITU) takes over
multirate standards for HDSL-2.
A 'Wild West' In Standards Issues
"It's a real Wild West out there in standards issues, now
that ANSI has turned over all multirate standards issues to
the ITU," said Dan Cordingley, director of telecom
marketing at chip maker Level One Communications, in
Sacramento, Calif. "We will be waiting on a little more
market certainty before developing the multirate chip set."
Amid the unknowns, semiconductor manufacturers are
rolling out entries for what they believe will be a significant
market, if DSL fulfills its promise and catches up with
cable modems as the broadband option of choice for
consumers. Yet a new round of chip introductions at
DSLcon betrayed concerns about the nagging issues of line
codes and multirate standards.
Level One launched its long-awaited HDSL-2 chip set,
while Metalink, in Tel Aviv, Israel, showed early FPGA
prototypes of a transceiver chip set that could handle both
SDSL-2 and HDSL-2 over the length of a full carrier
service-area loop.
Meanwhile, the ADSL Forum is trying to take on new
levels of responsibility by expanding its work in handshake
functions and SDSL/HDSL-2 services -- or as Jim
Southworth of Concentric Networks said, "taking the 'A'
out of the ADSL Forum." But a vendor coalition cannot
replace a true standards organization, developers complain.
While the University of New Hampshire (UNH) is playing a
role in the April to May Plugfest events, the results will be
kept private, open only to participating chip-set and OEM
vendors, making the Plugfests of little use to the DSL
community at large.
"This could be a real problem, if there is not a clear
certification authority," said David Long, strategic
marketing director at Alcatel Microelectronics, in Antwerp,
Belgium. "UNH has a great deal of experience in doing
interoperability tests, but nothing in Plugfest activities sets
it up as an official site. It may prove important to customer
acceptance to have such a facility."
And the heat is on, particularly in residential markets.
Claudia Bacco of TeleChoice warned in a presentation at
DSLcon on Wednesday that cable-TV modems still
maintain a tenfold advantage over ADSL in deployment,
with about 500,000 cable modems out in the U.S. market,
against 39,000 working DSL lines. Problems in the
residential space can be linked to the conservatism of
incumbent local-exchange carriers (ILECs), which are
trying to sidestep the requirement of fully qualifying all
their local copper loops.
Exceptions in the ILEC community are beginning to
emerge, such as the recent Bell Atlantic rollouts using
Alcatel equipment. But in general, the ILECs are marketing
xDSL almost as poorly as they did ISDN.
By contrast, the CLECs are banging the drum for SDSL
services among business customers, a trend evidenced by
the boom in the stock prices of data CLECs such as Covad
Communications and Rhythms NetConnections. OEMs
that focus on SDSL equipment for the new CLECs, such
as Copper Mountain Networks, are among the most
successful in the nascent DSL markets.
But opinions were almost universal at DSLcon that real
mass deployment means a residential market for ADSL
services, and that requires making systems easy to install
and maintain. Vendors are realizing the splitterless ADSL
standard may reduce maintenance-truck rolls from phone
companies -- a make-or-break consideration, given studies
showing that any service requiring more than one
maintenance visit per year to a customer site cannot be
provisioned cost-effectively. But it will in no sense
eliminate them.
In fact, the so-called "G.Lite" splitterless version of ADSL
requires microfilters on virtually all voice handsets in a
residence, to eliminate interference when an analog phone
is used on an ADSL line without an outdoor splitter. In
recent tests, Orckit Communications has conducted with
GTE, 81 percent of the test homes could not guarantee the
full speed of 512 kilobits per second upstream and 1.536
megabits per second downstream over a 15,000-foot loop
when the voice phone went off-hook.
Microfilters were required even when a phone was
on-hook, in 23 percent of the cases. In 50 percent of the
homes, multiple microfilters had to be installed, and power
cutbacks greater than 10 dB had to be implemented in
many sites to avoid audible interference with the voice line.
Padmanand Warrier, development-group leader for
broadband access at Texas Instruments, said consumers
can get used to phones with microfilters, if carriers
prepare now. Today's cost of $20 for a low-pass
distributed filter will have to plummet to make sure they
are widely used, Warrier said.
Practical issues of real-world deployment -- not just
microfilters, but also interfaces between
customer-premises equipment and DSL access
multiplexers (DSLAMs) -- will be addressed in the next
few weeks of Plugfests. Tests will begin near Alcatel
headquarters in Antwerp the last week of April, followed
by tests at the University of New Hampshire in mid-May.
While the specific results of Plugfests will be proprietary to
participants, general results on performance and
interoperability will be announced June 8 at Supercomm,
the week UAWG plans to declare its work completed.
Mark Peden, senior technologist for xDSL at Intel's
architecture labs, said OEMs and carriers will still have
plenty of work to do, such as developing splitterless-ADSL
solutions for digital loop carrier pedestals. But June will
represent an important demonstration that the ADSL
market is mature enough to show working deployment
models in which carrier truck rolls can attain the
reductions needed to make DSL a go.
The next critical factor for uniting DSL services will be for
the ADSL Forum to promote the G.994 handshake
algorithms, which define how a connection should be set
up. Ken Krechmer, technical editor of Communications
Standards Review, said the handshake function, or
etiquette, is the base on which all DSL services can be
handled universally, and is thus more important than the
ADSL Forum's expansion of its work to include SDSL and
HDSL-2.
Handshake Gets The Nod
At a meeting in Melbourne, Australia, the ITU agreed to
apply the handshake -- akin to the V.8 standard in analog
modems -- to all DSL services. The handshake also allows
for vendor-specific proprietary features, which Krechmer
termed "a key to preserving the ability to innovate within a
common standard."
The handshake is a 1-Kbps message sent before a
connection is established to specify how
customer-premises and DSLAM equipment from one
vendor (or a coalition of vendors) could perform unique
functions on top of standard xDSL transmission functions.
The scheme allows for broader differentiation.
On the chip front, Level One is launching its HDSL-2
solution, fully aware that the chip set will have to reduce
its 4-watt power dissipation to be a true vehicle for
providing businesses with symmetrical T1 speeds over a
single copper pair. Taufique Ahmed, product-line manager
for DSL at Level One, said a much lower-power
single-channel transceiver will be required, along with a
multichannel device for telco central offices that preserves
the full performance of the Optis line code in HDSL-2.
Cordingley of Level One said the DSP cores in the HDSL-2
chip set are programmable enough to offer multirate
performance in a future SDSL-2 standard. Beyond that,
Level One is waiting for the market to settle before crafting
a multirate entry.
Metalink, which has enjoyed an edge in European SDSL
deployment because of its early expertise in 2B1Q codes,
has updated its TurboSDSL solution, which allowed
symmetrical speeds up to 2.3 Mbps, based on a
near-maximum-likelihood algorithm. The core chip set has
been tweaked to implement Optis coding and early
prototypes were shown at DSLcon.
Danny Gur, president of Metalink's U.S. operations, said
carriers can use flexible mixes of loop lengths and
PAM-code implementations to opt for 2B1Q/ PAM-4 for
first-generation systems, and full PAM-16 with Optis
spectral shaping for HDSL-2-compliant systems.
"We are looking at multirate for data and voice access, and
HDSL-2 for a T1-only solution," Gur said.
Conexant Systems, in Newport Beach, Calif., will be
leveraging the programmability of its ZipWire architecture
as the HDSL-2/SDSL-2 standards come online. Ron Cates,
director of commercial DSL products at Conexant, said
details of a next-generation chip set are still a few weeks
away, but Conexant plans to offer a chip with separate
modes supporting 2B1Q and PAM/Optis codes.
A new company founded by Octel Communications
executives, Telocity, in San Jose, Calif., has launched a
Web-based DSL provisioning service based on its own
intelligent DSL modem, the InterChange 1000. Telocity's
goal is to allow a customer to sign on for multiple aspects
of DSL services without carrier intervention. |
