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Digital Subscriber Line (DSL) Guide
By Bruce Stewart,
Forget tying up your phone line for Internet access! Learn how
DSL works, where it's headed, and how you can get it.
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. DSL is definitely on the rise, and has made a serious
challenge to the cable modem market in the last few years. TeleChoice,
Inc. forecasts 17.4 million DSL lines installed by the end of 2004.
If you've been wondering what exactly this new technology is, 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 look 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 resources.
Bruce Stewart is a freelance technology writer. He covers Web software,
operating systems, the wireless industry and contributes regularly
to ZDNet.
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
existing POTS lines--Plain Old Telephone Service--which allows the
phone companies to provide this service without costly installation
of higher-grade cable.
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 counterintuitive, but that is one of the real strengths
of 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 when discussing DSL technology. 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 in general.
ADSL The most common service, and the one you'll be looking at
if you're considering home DSL Internet access, is Asymmetric Digital
Subscriber Line (ADSL). ADSL can support downstream bandwidths of
up to 8Mbps and upstream bandwidths of 1.5Mbps. By comparison, a
T-1 connection also provides 1.5Mbps. As the most common form of
DSL, the "A" is often dropped, and when someone is just talking
DSL, it's probably ADSL.
Variations of ADSL An important variation of ADSL is called G.Lite,
DSL-Lite, or UADSL (Universal ADSL), a notched-down version aimed
at the immediate consumer market. Whichever the name, this service
provides speeds up to 1.5Mbps downstream and 384kbps upstream. Another
similar offering is CDSL (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 90's,
as an improved way to provide T1/E1 (1.5/2.0Mbps) 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. Since both
HDSL and SDSL are symmetric forms of DSL technology, 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 52Mbps downstream and 13Mbps
upstream.
Believe it or not these aren'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 works well for two types of applications--interactive video
and high-speed data communications. High-speed data services break
out into two main areas: Internet access and remote LAN access,
the realm of telecommuters. In this article, we'll focus on using
ADSL for high-speed Internet access.
Besides higher bandwidth, some of the advantages of ADSL access
from telephone companies are that there are no per-minute charges,
and you get 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
involved 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
was made in June 1999. At 1.5 Mbps downstream and 386 Kbps upstream,
G.Lite DSL is still 8 to 10 times faster than the ISDN services
offered today for Internet access, and more than 25 times faster
than 56k modems.
Another ADSL standard, called G.dmt, is competing with G. Lite.
G.dmt is also known as full-rate ADSL and supports speeds of up
to 8-Mbps downstream and 1-Mbps upstream.
As the phone companies continue to aggressively roll out broadband
offerings, there will be a dramatic change in the number of people
who 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.
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 a DSL access option is
to call your local phone company, or visit their Web site. All the
carriers offering DSL have it prominently advertised on their site,
and many offer 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 online form that will check DSL availability in your area,
visit either the DSL.com or .Getspeed.com
Most modern computers can easily be equipped to connect to a DSL
service. This is accomplished by connecting an ADSL modem, which
is a significantly different beast that your traditional analog
modem, to an Ethernet network (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 66MHz 486 processor or a Macintosh
with at least a 68030 processor, and 16MB 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 also 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 data 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 your computer.
With G.Lite ADSL, there will be no need for an installation visit.
You will 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 charge 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 provider.
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 $40 mark,
which conventional wisdom says is necessary for widespread acceptance.
DSL providers typically offer several different pricing/bandwidth
options. Today, you may pay anywhere from $19 to $80 a month for
a basic ADSL service that provides 384kbps downstream and 128kbps
upstream. For higher bandwidth options, the price obviously climbs.
A typical 1.5Mbps downstream/384kbps 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, rest 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 good to be true, there are potential drawbacks. For example,
there are fairly strict distance limitations that DSL circuits can
operate within. To receive G.Lite ADSL, a customer typically has
to be within 18,000 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 the distance requirement of a central office equipped for
DSL, it still may not work if your neighborhood or building has
deteriorating telephone cable . In these 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
telephone handsets, or poorly functioning telephones. It may be
necessary to install bypass filters at offending telephone jacks,
or replace some telephone instruments.
High growth is expected in this industry from all corners, especially
in the next several years. TeleChoice, Inc. estimates that installed
domestic DSL lines will reach 10 million by mid-2002, and 17 million
by 2004. In comparison, Dataquest estimates that there will be 14
million cable modems in use in the U.S. by the end of 2004. The
FCC projects that the DSL subscriber base will grow to 10.1 million
by the end of 2002, whereas the cable modem user base will be around
9.1 million.
DSL technology has continued to get easier and cheaper to use,
which can only help in the battle with the cable companies for the
residential broadband market. Maybe this is why TeleChoice reports
a 366 per cent increase in DSL subscriber growth from 2000 to 1999,
and predicts 142 per cent growth for this year.
The bottom line is that while it may be difficult to get a DSL
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.
Online resources Here are two of
the best sources of DSL information on the Web:
TeleChoice xDSL.com
EverythingDSL.com
Here are links to some of the major service providers and lots
more DSL information:
US West Megabit
Services
Pacific
Bell FasTrak DSL
Verizon OnlineDSL
Bell South FastAccess
ADSL
Westell
Aware Inc.'s
xDSL Glossary
ADSL Resource Guide
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