The company that invented digital-subscriber-line
technology signaled last week that it believes that market conditions have finally reached
the point where it makes sense to introduce products supporting the delivery of high-speed
data over telco lines.
Lucent Technologies Inc. -- the Bell Laboratories unit of
which developed the modulation techniques that spawned what is now known as ADSL
(asymmetric DSL) -- said it will supply a chip set supporting the delivery of data at 1.5
megabits per second to households over existing plant and in-home wiring. The company also
said it will supply adjuncts to its switching gear that are designed to interoperate with
products based on the new chip set.
Lucent's move is part of an industrywide push toward
standardization of techniques supporting 'ADSL-Lite' that has the backing of
Microsoft Corp., Intel Corp. and Compaq Computer Corp., as well as the major telcos,
officials said.
Most suppliers of DSL gear in the past few months have
offered various approaches to this version of the technology, which, rather than pushing
modulation to the highest speed capabilities, settles on a 1- to 1.5-mbps downstream
throughput in the interest of achieving broader market coverage and simplifying customer
installation.
'Our customers' expectations regarding data
speeds have dramatically changed,' said Ken Brivel, strategic marketing manager for
DSL products at Lucent's Microelectronics Group. 'They want a platform for the
mass market that doesn't require them to install a splitter on the wall of the
subscriber premises and to run a separate wire to the PC [personal computer].'
Rather than competing with other ADSL-system suppliers,
Lucent has decided to market its new chip set to original-equipment manufacturers, much as
it has marketed chips for analog modems, such as the 56-kilobit-per-second units.
At the same time, with its switches installed in over
one-half of the central offices in the United States, Lucent sees the supply of new
DSL-interface equipment for its switches as a strong incentive for system suppliers and
telcos to move forward with DSL.
'The ability to plug in a DSL system to our embedded
base of switches adds a lot of value to the end-to-end solution,' said Linda
Manchester, director for access-business management and strategy at Lucent's
Switching and Access Group. 'Given the fact that the chip set is programmable, using
our approach doesn't eliminate the customer's ability to use other types of
approaches to DSL.'
The chip sets, due for delivery in limited quantities in
the third quarter, are based on a new generation of digital signal processors developed by
Lucent. These chips have sufficient processing power to support multiple levels of
throughput and other service features, including the ability to operate as 56-kbps analog
modems in instances where a subscriber's line won't accommodate the digital
throughput, Brivel said.
Until recently, manufacturers were targeting product
development on the assumption that telcos were positioning DSL -- at least initially -- as
a technology to serve professional users in the home and small-office markets with
high-speed-data services, which put a premium on delivering data at the highest possible
speeds. As a result, all trials and early commercial introductions of DSL technology to
date have focused on the use of systems that typically require separate in-home wiring in
order to minimize noise impediments to optimum throughput.
The telcos' sudden shift to a stronger emphasis on DSL
as a mass-consumer product has sparked a scramble among suppliers looking to offer a more
robust, easier-to-install system, with no clear sign yet as to which approach will
prevail.
'This is in our product plan, but there are a number
of issues that need to be resolved,' said Steve Makgill, director for ADSL-product
management at Alcatel, which is supplying SBC Communications Inc., Ameritech Corp. and
BellSouth Corp. in early commercial rollouts.
One step that the industry needs to take is to compile
information that will provide suppliers with a better picture of what the true line
conditions are at customers' premises, Makgill said.
'There's a need for more information before we
can say what the bandwidth limitations are and what the ultimate coverage will be for
providing services without the use of splitters and separate wiring,' he said.
But getting to an agreement on which techniques will be
used and which specifications they'll support is seen as vital in an industry that
has witnessed the effects of consumer confusion over competing standards for 56-kbps
modems, Makgill added. Whichever approaches are taken, he said, the technology will
probably be able to reach in the neighborhood of 80 percent to 90 percent of all
households.
Alcatel and its customers have committed themselves to the
DSL-modulation technique known as DMT (discrete multitone), which appears to be prevailing
as the industry's standard, despite strong competition from other methods.
'All of our customers are telling us that they want us
to take this approach,' Manchester said.
While refusing to discuss specific customer needs, she said
the client base that the new Lucent system is targeted to includes Bell Atlantic Corp. --
notwithstanding that carrier's long-standing support for CAP (carrierless amplitude
phase), the leading modulation alternative to DMT. But even with uniform agreement on
modulation, there are still fundamental protocol issues that must be resolved, she added.
One issue involves the approach taken to reducing the
effect of noise caused by ingress and reflections in premises wiring. If the system
doesn't use all of the RF carriers in the DMT-modulation scheme to deliver maximum
throughput -- which, in the newest systems, goes all the way to 8 mbps over line distances
of up to 12,000 feet -- there is more room to accommodate noise by allocating some
carriers as noise bearers and others as information bearers.
While all DMT systems segment POTS (analog plain old
telephone service) from digital data by assigning POTS to the lower range of the 1.1
megahertz of available line bandwidth, there are still variations in how vendors use DMT
in the higher frequencies to combat line noise, Brivel said.
'DMT uses many different carriers, so different
vendors eliminate different carriers,' he said.
Beyond the actual modulation variations, there are other
protocol issues to be resolved, even within the DMT platform, Brivel added.
'Differences in how the modems talk to each other, in
what the algorithms are in the start-up sequence and other things of that nature have to
be ironed out,' he said.
But because these last items are in the software-protocol
layer, changes can be relatively easily implemented over programmable chips, such as those
offered by Lucent, once agreement is reached on universal standards, Brivel said.
The hardware piece is another matter, and that is where
Lucent and the other vendors must focus on ironing out differences to ensure that telcos
have a deployable mass-market platform within the next year or so.
