If you've been paying attention to the press lately, you know that DSL
(Digital Subscriber Line) is the hottest trend in high-speed Internet
access. But if you've been wondering what exactly this new technology
or how you may benefit from it, this article's for you.
First, we'll sort through the alphabet soup of acronyms surrounding DSL
technology. Then we'll explain how this technology works, and take a
at where it's currently available. We'll also go through all the steps
involved in setting up your system, and provide plenty of online DSL
DSL is definitely on the rise, and is expected to replace ISDN and make
serious challenge to the cable modem market in the next few years.
TeleChoice, Inc. forecasts over one million DSL lines installed by the
of 2000. So let's get to know this rising star.
Digital Subscriber Line service is a high-speed data service that works
over copper telephone lines and is typically offered by telephone
companies. The real beauty of DSL technology is that it works on
POTS lines -- Plain Old Telephone Service -- which allows the phone
companies to provide this service without costly installation of
DSL uses a different part of the frequency spectrum then analog voice
signals, so it can work in conjunction with your standard analog POTS
service, sharing the same pair of wires.
This may seem counter-intuitive, but that is one of the real strengths
this technology -- it can piggy-back right on top of your existing phone
line, without even disturbing that service. You can even use your analog
portion of the phone line as a modem or fax line, while simultaneously
using the data portion for your DSL access.
Not surprisingly, there's a slew of terms and acronyms that get used
discussing DSL technology. Starting at the beginning, DSL refers to a
digital subscriber line that a telephone company central office provides
to an end user.
There are a host of versions and flavors of DSL, which has led to the
common designation of "xDSL" when referring to this type of technology
The most common service, and the one you'll be looking at if you're
considering home DSL Internet access, is ADSL, for Asymmetric Digital
Subscriber Line. Being the most common form, the "A" is often dropped,
when someone is just talking DSL, it's probably ADSL.
ADSL can support downstream bandwidths of up to 8 Mbps and upstream
bandwidths of 1.5 Mbps. For comparison, a T-1 connection also provides
An important variation of ADSL is called G.Lite, DSL-Lite, or UADSL
(Universal ADSL), and is a notched-down version aimed at the immediate
consumer market. Going by many names, this service provides speeds up
1.5 Mbps downstream and 384 kbps upstream. Another similar offering is
(Consumer DSL), which is a smaller-bandwidth Rockwell variation.
Some of the other variations include HDSL (High-bit-rate DSL), SDSL
(Symmetric DSL) and VDSL (Very-high-bit-rate DSL).
HDSL was the original form of DSL technology, developed in the early
as an improved way to provide T1/E1 (1.5/2.0 Mbps) services by the
telephone companies. It uses 4 copper wires (2 pairs) and offers a wider
coverage area than previous methods.
SDSL, also sometimes called HDSL-2, is an enhanced version of HDSL that
allows it to work with only one pair of wires. It accomplishes this with
only a slight (.2 km) decrease in loop length.
Both HDSL and SDSL are symmetric forms of DSL technology, which means
they have the same bandwidth capability in both directions.
VDSL, also sometimes called BDSL, is targeted at high-access demanding
companies and can support speeds of 52 Mbps downstream and 13 Mbps
Believe it or not this isn't even all of the xDSLs. For a great online
reference of terms and abbreviations that you may come across in the DSL
world take a look at Aware's xDSL Glossary ADSL (Asymmetrical) is the type of DSL being offered for high-speed
Internet access. It is asymmetrical because it provides different
bandwidths in the upstream and downstream directions, giving the user a
much bigger "pipe" in the downstream direction.
This scheme works well for the typical Internet user -- where upstream
communication is usually small (link requests) compared to downstream
communication (Web pages with graphics, downloads).
An ADSL circuit works by connecting an ADSL modem on each end of a
twisted-pair telephone line, creating three information channels -- a
speed downstream channel (to your home), a medium speed upstream channel
(from your home), and a POTS voice channel.
The ability to provide separate voice and data "channels" on the same
is one of the aspects of DSL technology that makes it so attractive to
telephone companies. Standard ADSL service requires the use of a
on both ends, to separate the voice channel from the data channels.
One advantage of being able to split the data and voice like this is
phone companies can keep them on separate networks. The Internet data
can stop clogging up the PSTN (Public Switched Telephone System) and be
sent directly to the packet-switched network.
With the advent of G.Lite DSL, the service can now be deployed to homes
without even the need for a telephone company installed splitter --
addition to its other acronyms this service is often referred to as
The exciting promise of DSL lies in this ability to implement the
easily with existing phone wiring. By being able to offer a
high-speed data service that will work on your existing phone line --
be turned on without any installation visit -- the potential audience
rate of deployment far surpasses other high-speed options.
ADSL works well for two types of applications, interactive video and
high-speed data communications. High-speed data services break out into
main areas, Internet access and remote LAN access, the realm of
telecommuters. In this article we focus on using ADSL for high-speed
Besides higher bandwidth, some of the advantages of ADSL access from
telephone companies are that there are no per-minute charges, and you
an "always-on" connection for your monthly fee.
G.Lite ADSL was developed as a cheaper, lower bandwidth version of ADSL
service, that could be turned on without a visit from a telephone
technician. Companies like Microsoft, Compaq and Intel have been
in the G.Lite effort, all hoping to establish a high-speed data service
that is as easy for consumers to install as today's analog modems.
In late 1998, G.992.2 was adopted by the ITU as the standard that began
as the G.Lite. Formal ratification of the new G.992.2 standard is official as of June
1999. At 1.5 Mbps downstream and 386 Kbps upstream, G.Lite DSL is still
10 times faster than the ISDN services offered today for Internet
access, and more than 25 times faster than 56k modems.
Most providers are not yet offering G.Lite ADSL service, but you can
expect this to change in the near future. If you order an ADSL service
today, you will most likely still need a technician to visit and install
an ADSL splitter.
There will be a dramatic change in the number of people can get DSL
services. Up until recently, you had to be in a select area, usually
involved in a carrier's field test. Now, however, the rate of deployment
is picking up.
DSL providers have been announcing aggressive implementation plans this
year. In January, SBC Communications (parent of Pacific Bell,
Bell, Nevada Bell and SNET) announced plans to have DSL service
to over 8 million residential customers by the end of 1999. Bell
met the challenge and promised to make their DSL offering available to
another 7.5 million customers by year's end.
AOL is working prominently with both companies, and is offering
access to their service to these customers.
One consideration is that with today's DSL you have to be within 18,000
feet of the telephone company central office, and sometimes less.
Estimates have placed just over half of US residences within DSL range
of their central office.
The easiest way to find out if you have DSL access as an option is to
your local phone company, or visit their Web site. All the carriers
offering DSL have it prominently advertised on their site, and many
specific telephone number look-up services, to determine if you are in a
qualifying area. Ordering the service from a telephone company is done
just as ordering any other telephone line.
For an extensive and up-to-date list of DSL trials and offerings visit
ADSL Forum's ADSL Deployments section.
Most modern computers can be easily equipped to connect to a DSL
This is accomplished by connecting an ADSL modem, which is a
different beast that your traditional analog modem, to an Ethernet
(NIC) card in your PC.
Today, ADSL modems are external devices that accept the data line from
the telephone company, and provide a 10-baseT Ethernet interface to
connect to your computer. (Expect to see internal ADSL modems very
soon.) Many computers today come with built-in Ethernet capability, but
don't worry if yours doesn't. The cost and installation of the network
card is generally included by the DSL provider.
The basic requirements for a system to work with today's ADSL modems is
either a PC with at least a 66 MHz 486 processor or a Macintosh with at
least a 68030 processor, and 16 Mb of memory. Of course performance will
improve with faster processors and more RAM on either platform.
Getting started with ADSL Internet access is quite a bit different than
with a regular dial-up ISP. You will either be dealing with your local
telephone company -- the provider of the ADSL service -- or an
ADSL-equipped ISP who will coordinate with the phone company.
In many cases the telephone companies offering the ADSL services are
getting into the ISP business, and they may handle both aspects of the
service for you. This can simplify billing and service considerations.
With traditional ADSL services, a technician will install a splitter at
your telephone line point-of-presence. This device will split out the
standard analog voice line that gets wired to your home jacks, and the
line that gets connected to an ADSL modem.
If you are not dealing with your local telephone company, you will most
likely need two separate installation visits to get it all going. First
the ISP will arrange for the telephone company to turn on the DSL line
and install the splitter at your home, then a technician will come and
install your ADSL modem on this line, and possibly the network card in
With G.Lite ADSL, there will be no need for an installation visit. You
simply order the service, install the ADSL modem, and plug it into your
regular telephone line.
The ADSL modem is generally provided by the DSL provider. They may
you up to $200 for this device, discount it heavily or even throw it in
for signing up. There is often a monthly rental option as well. At this
time you must use the brand and model of ADSL modem specified by your
Costs for DSL services vary more than cable modem services, though this
area has recently been getting more competitive. There has been a strong
effort to get monthly costs down below the $50 mark, which conventional
wisdom says is necessary for widespread acceptance.
DSL providers typically offer several different pricing/bandwidth
Today, you may pay anywhere from $39 to $80 a month for a basic ADSL
service that provides 384 kbps downstream and 128 kbps upstream. For
higher bandwidth options the price obviously climbs. A typical 1.5 Mbps
downstream / 384 kbps upstream connection will be in the $100-200 range.
Of course there are installation and set-up fees as well. These also
vary greatly, and are often waived or reduced for one-year commitments.
Typically, installation fees range from $200-$400.
Whatever the specific arrangements your ADSL provider makes with you,
assured they will be much more involved in setting up your
connection than a standard dial-up Internet service provider.
While the speeds and costs associated with DSL access seem almost too
to be true, like any technology there are potential downsides.
There are fairly strict distance limitations that DSL circuits can
within. To receive G.Lite ADSL a customer typically has to be within
feet of the central office -- not always an option. DSL services that
provide greater that 1.5 Mbps require even shorter distances to the
central office, usually 10,000 to 12,000 feet. Compare this to a cable
modem that can be located up to 30 miles away from the service provider.
The quality of the wiring is an issue as well. Even if you live within
requirement of a central office equipped for DSL, if your neighborhood
building has deteriorating telephone cable it still may not work. In
cases the local phone company may be able to provide a "cleaned" or
"conditioned" line for you, but you will pay dearly for this.
In some instances DSL circuits can suffer from interference from
handsets, or poorly functioning telephones. It may be necessary to
by-pass filters at offending telephone jacks, or replace some telephone
High growth is expected in this industry from all corners, especially in
the next several years. TeleChoice, Inc. estimates that installed
DSL lines will reach 500,000 this year, and one million before 2001.
With less than 25,000 installed lines by the end of 1998, this is some
pretty serious projected growth. There is no disputing that DSL's
competition in the residential high-speed Internet access race, cable
operators, have a strong lead.
For comparison, Kinetic Strategies, Inc. estimates that there were
cable modems in use in the U.S. by the end of 1998, and they are
to reach the million mark during the third quarter of 1999. Forrester
Research predicts cable modems will have 80 percent of the broadband
The bottom line is that while it may be difficult to get an ADSL line
today, there is every reason to expect very rapid deployment of these
services in the near future. The greatest strength of this technology is
its ability to reuse existing copper phone lines, which gives DSL a real
advantage in ease of deployment, compared to other high-speed options.
Here are the two best sources of DSL information on the Web:
Here are links to some of the major service providers and lots more DSL
US West Megabit Services
Pacific Bell FasTrak DSL
Bell Atlantic Infospeed DSL
Bell South FastAccess ADSL
Cincinnati Bell ADSL Zoomtown
Alcatel's ADSL Brochure
Aware Inc.'s xDSL Glossary
SAS ADSL Resource Center
ADSL Resource Guide