|GETTING IN THE FLOW OF DSL
ALTHOUGH DIGITAL SUBSCRIBER LINE TECHNOLOGY ISN'T NEW,
THE DEMAND FOR IT IS: THE INTERNET IS DRIVING NEW INTEREST IN THE SERVICE
THAT SOME SAY WILL DELIVER VOICE AND DATA EFFICIENTLY AND CHEAPLY.
Tribune Staff Writer
September 20, 1999
DSL is the latest high-tech buzzword,
intoned on radio commercials and splashed on the sides of CTA buses.
But the technology that boosts data flow over pairs
of traditional copper phone lines isn't very new at all, tracing its history
over the course of 30 years' work at Bell Laboratories. In fact, this is
the second time telephone companies have made a run at selling the technology
to the public.
In the early 1980s,
just before the breakup of the Bell system, the phone company's marketing
people created a campaign for packet-switched service that would provide
voice, data and video over a single copper line. They used cherries, pears
and apples as symbols for each service flowing along in a big fruit salad
Nothing much came of the marketing effort because
demand was low for data transmission and nearly non-existent for video
back in those days, so the technology was shelved.
But it wasn't forgotten.
Bell engineers continued to tweak and develop packet-switch
technology, and they trotted it out again in the early '90s, when some
regional Bell companies flirted briefly with the notion of video-on-demand
that would enable customers to watch movies at home delivered over their
phone system's copper lines.
When interest in video-on-demand petered out, the
engineers continued development work on DSL, or digital subscriber line,
technology on the general theory that something that could magnify the
efficiency of the existing copper phone lines so dramatically would some
day find acceptance.
"DSL failed in the early days because it is tough
for us to force the customers to do something different, like video-on-demand,"
said Michael Meyers, director of marketing development at Lucent Technologies
Inc., the current incarnation of Bell Labs.
"But now the Internet is the driver. People want
faster access to the Internet, and DSL can provide that. When you also
have government deregulation of the phone business and the rise of competing
phone companies looking for a technological edge, everything is coming
together to really promote DSL."
And now that there is demand, the engineers are
eager to provide products to meet it. Lucent and others have hardware and
software for phone companies that enable them to digitize and send voice,
video and data in packets over copper lines in a profusion of pears, cherries
This is in contrast to traditional circuit-switched
architecture that provides one dedicated pair of copper wires for each
Phone companies long ago began to digitize signals
sent over great distances, but they have kept to the circuit technology
when carrying conversations to and from neighborhoods. What DSL does is
to digitize and packetize the signals in and out of the customer's premises,
said Tony Grewe, a Lucent director of strategy and business development.
As virtually all local phone companies embrace DSL
technology to carry data at high speeds and to provide several voice channels
over a single pair of copper wires, network costs will drop dramatically
and the entire telecommunications industry is in for several years of radical
In Illinois, for instance, experts predict the current
complex local phone service billing formula that uses time and distance
of calls to calculate charges will be swept away by flat-rate deals.
But as useful as DSL may be, it still has many limitations.
For one thing, it works really well for customers
who are very close to the phone company's central switching office, but
not so well for customers who are a few miles away.
In some localities, DSL technology may not be practical
for 25 percent of the customers. But one reason for that is that today's
circuit-switched network was never designed with DSL in mind. As DSL becomes
more widely deployed, it's likely that service providers will find ways
to reach far-flung customers with it.
Engineers say it's still early days in advancing
DSL technology, and the more experience they get in using it, the better
its performance will become.
In fact, to address the various trade-offs that
engineers must make when designing a DSL system, they've come up with a
whole family of DSL, about eight different flavors of the technology at
If the technology were still named for fruits, it
would be a regular farmers' market by now.
One significant distinction in DSL is whether a
service is symmetric or not. Asymmetric DSL refers to a system that enables
the customer to send data upstream to the central office at a much slower
rate than he obtains data flowing downstream.
ADSL is designed for customers at home who mostly
want access to the Internet, which finds them sending brief messages upstream
to access gushers of data coming back to their home computers.
The flip side of ADSL is symmetric DSL, or SDSL,
which is better suited to people working at home who exchange large data
files with their colleagues in the office, often sending out as much data
as comes back to them.
Another flavor is VDSL, a very high bit-rate flavor
intended to work at quite short distances that is geared toward video streaming.
This service works well in areas where optical fiber, the granddaddy of
big capacity pipes, is nearby and the copper need only carry signals a
fraction of a mile from the fiber end point.
A home consumer product called DSL Lite was developed
to make the service easier to install with minimum expense. A limitation
to the Lite version is some loss of transmission speed for transporting
Even though DSL technology is more than two decades
old, it still has much development ahead of it, said Amra Tareen, Lucent
director of Internet product development. Growing popularity of DSL assures
that the technology will just get faster and cheaper, she said.
"This isn't an exact science," said Tareen. "Chip
sets will improve speeds as we understand the performance parameters better.
The same thing that happened with dial-up modem technology will happen
The demand that's causing phone companies to deploy
DSL is also causing them to install more optical fiber connecting the network's
backbone closer to the neighborhoods, said Lucent's Meyers. The various
DSL flavors can complement fiber nicely as phone service providers bring
more network capacity, or bandwidth, closer to their customers.
But despite the excitement it is now generating,
DSL's debut also brings a host of problems that promise a bumpy road for
phone service providers and their customers.
One potential problem is that the various flavors
of DSL can interfere with each other when they run on copper wires that
are wrapped together in bundles.
Judith Hellerstein, author of a DSL technology report
for the Chicago-based International Engineering Consortium, said that "we
will have problems with interference and crosstalk stemming from wrapping
SDSL with ADSL lines. It's not a problem now because these technologies
aren't mass-deployed, but once they are, it will cause interference and
static for voice calls."
Besides technical issues that underlie DSL deployment,
cultural and political factors also dog the industry's adoption of the
new technology, Hellerstein said. For example, there are industry standards
for some flavors of DSL but not for others, and one reason for that is
"The competitors who are deploying SDSL now are
working on `Internet time' that says you want to get the first mover advantage,"
Hellerstein said. "If you wait, you lose. Well, Internet time is lightning-fast
compared to telecommunications utility time, which governs how standards
"It can take years to hold meetings, measure performance
and gain consensus. It took two years for the ADSL working group to come
up with ADSL Lite, and that was considered fast."
For economic reasons, the large incumbent local
phone companies like Ameritech Corp. are deploying ADSL and marketing it
mostly to residential customers. They do this because of competition from
cable TV high-speed Internet connections and because they already offer
expensive high-speed data connections called T1 lines to many business
Competitive phone companies like NorthPoint Communications
Inc., based in San Francisco, usually offer SDSL because their customers
are mostly small businesses that cannot afford T1 lines but are happy to
get high-speed data services for $100 or $200 a month instead of $500 or
$1,000 that T1 connections fetch.
The standards groups are often dominated by the
large incumbent carriers who favor ADSL, said Hellerstein, so there is
fear that in the future there will be industry pressure to alter the unstandardized
SDSL connections to alleviate interference problems that arise.
"Even though there's an industry consensus that
DSL is the future, and it's in everyone's interest to cooperate on setting
standards and avoiding interference, there's no way to act quickly," she
"All they can do is work out the fixes now and apply
them to subsequent product offerings."