Cable Modems vs. Digital Subscriber Lines

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Cable Modems vs. Digital Subscriber Lines
Bob Fager
Econ 235ഊThe Internet has grabbed on to the world and it isn't letting go. Nearly 36 million U.S. homes currently have PCs
and everyone is dying to jump on the information
superhighway. The Internet, which started as a group of
government agencies and universities, has grown to include
almost anyone, from home users to large companies and
everyone in between. It makes sense then that providing
Internet service is big business. The service which used to
be dominated by groups of nerdy computer whizzes using
equipment in someone's basement is now being provided by
many telephone companies, large on-line services and may
soon be available from you local cable company.
Computer users are an impatient group. They are
starving for a faster way of connecting to the ‘net. Until
now home users have had to suffer with the slow connections
available with analog modems or spend a relatively large
amount on having a digital line, such as ISDN, installed and then continue paying a lot for the monthly charges
associated with such lines.
Standard analog modems have always been hindered by the
bandwidth they are allowed to use. Standard voice grade
phone lines use the frequency spectrum between 0khz and 4khz to transmit their signal. 33.6 kbps modems packed nearly 11
bits of data per hertz, a remarkable feat, which is very
near the theoretical limit. To allow faster connections
modems must use a wider bandwidth.ഊTwo new competing technologies are now being developed which use this broadband idea to give computer users the
speed they crave. Telephone companies are working on
developing a way to use the standard twisted pair copper
wires that now connect nearly every home in America to
transmit data at high speeds. These technologies,
collectively called xDSL, come in two main flavors. ADSL,
which is an acronym for asymmetric digital subscriber line,
is the most common. This name was coined by Bellcore in
1989. The other main type of digital subscriber line is
called HDSL. It stands for high-bit-rate digital subscriber
line. These two technologies are essentially the same,
except they apportion a different bandwidth to upstream
(user to network) and downstream (network to user) data
Concurrently, cable television providers are working on
technologies to allow them to connect computers to their
network and allow users to connect to the Internet at speeds just as high. Such equipment is being called a cable modem.
Cable modems offer the possibility of transferring data
at rates up to ten megabits per second, a speed nearly ten
times faster than that of ISDN and about twenty times faster than today's fastest analog modems. This number is somewhat
misleading however. The truth is that in order to actually
achieve that speed you must be the only user on the network. The reason for this is that this throughput is shared by
everyone connected to a given line. Typical cable systemsഊserve 500 to 2500 homes on one line. Therefore the actual throughput will depend upon how many other people in your
neighborhood are also trying to access the ‘net. Actual
speeds vary greatly.
Cable modems are already being used in several limited
areas, mostly large metropolitan areas, especially in
Southern California. According to research by The Yankee
Group there are approximately 25,000 people already using
cable modems. They expect this number to grow to around
275,000 by the end of 1998 (Tedesco).
The reason cable modems are not already widespread is
that they present a bigger technical challenge to cable
operators than anything they've ever faced. Cable companies
do not have a very good track record. They've given us lots
of unfilled promises – 500 channels of television,
interactive television and low priced telephone service.
Before cable operators can offer service to cable modems
they must upgrade their network. Only...
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