| Among the new waves of technology washing ashore in recent years are cable
modems - devices for gaining very high-speed Internet access through a cable
television network.High bandwidth technologies like cable modems are
important to teleworkers… if the technology isn't as fast at home as in the
office, then neither is the worker. AT&T has been investing heavily in enhancing cable infrastructures,
working to offer Internet, cable TV and telephone access through these networks.
At the heart of this strategy lies the cable modem: Why is it needed? What is
it? What does it do? How does it do it? And how do you get one?
What is it? While similar in some ways to the analog modem you may
currently have, a cable modem is much more powerful - theoretically, as much as
up to 1,000 times faster. (Throughput, however, actually never reaches
theoretical speeds outside of controlled lab conditions, just as your 56k modem
never reaches its top-rated speed.)
What does it do? A cable modem is still the fastest Internet service
for your home. Adding to the speed boost is the "always on" Internet
connection that doesn't require dialing in every time you want to go online. And
you can continue to receive television over the same cable, while data services
can be shared by up to sixteen PCs in a home-based LAN configuration.
How does it do it? With cable modems, users served by a
"node" (from 200-2000 homes, depending on the provider) share the
available bandwidth. A key component is the central transmission facility, known
as the "head-end". Subscribers connect to the head-end, which connects
to the Internet and to satellite television transmission systems. Privacy and
security, data networking, and quality control are integrated into the network
at the head-ends.
Upstream and down.The cable modem converts data signals into a form
suitable for rapid transmission. Data moving from the cable network to you is
known as "downstream" data, while "upstream" data moves from
you to the network. (Because most cable networks were built for television, some
cable modems use a telephone line to transmit data upstream.)
Downstream data is designed to move faster, while upstream data is sent at
variable speeds managed by the head-end. Data rates can be configured to meet
different user needs. For example, an e-commerce business needs to send and
receive at higher speeds, while a residential user is normally set up to receive
at a relatively high rate and send at a slower one. After all, as a single user,
most of what you're sending "up" is keystrokes and mouse-clicks,
whereas what's being sent "down" to you is more substantial - text,
images, streaming audio and video, and so on.
The upstream data you send is placed on a fiber optic backbone, which carries
traffic across your regional provider. This is the fastest part of the trip.
Here, data moves at rates near the speed of light. For the rest of the journey,
your data may encounter slower media - copper wire - as well as "choke
points" where it has to wait its turn. On the return trip, the head-end
combines the downstream data with the television video and audio and sends the
composite signal to you. The signal is re-divided at your house so that the
television signal goes to your TV and the Internet data goes to your PC.
In almost all cases, cable modem users
will see speeds that exceed an ISDN connection.
Performance: A cable data network is similar to an office local area
network (LAN) on a larger scale. The local cable provider manages an extended
Ethernet network over a wide geographic area. If you were the only user served
by a neighborhood node on this network, you'd have all the bandwidth to
yourself. When all your neighbors also have cable modems, speeds go down
somewhat - just as heavy traffic slows down rush hour, a high volume of users on
a node reduces data throughput (especially if they're using lots of bandwidth to
view streaming media, for example). Cable providers will usually add a node to
an area to ease such congestion.
Some Internet content is cached (temporarily stored) at the head-end to
provide users with quicker access. Of course, not all web content can be cached,
and so your request may travel beyond the head-end and across the Internet. Once
you're beyond the head-end, you're on the same Internet as everyone else and
subject to the same delays. But in almost all cases, cable modem users will see
throughput to the cable head-end and to the wider Internet at speeds that exceed
those of an ISDN connection.
While definitive statements about actual speed are impossible, the
perceptible difference between regular and cable modems is dramatic. Web pages,
especially "popular" ones, pop up instantly. Large files download in
seconds. Streaming audio and video activate without perceptible delay. This all
nets out (no pun intended) in leaps in productivity - more working time and less
"hourglass" time.
I'll Take One! By now, you may be asking, "So, where do I sign up?"
You can begin by going to www.home.com, the
online source for @Home cable modem services. Click the highlighted link for
"Can I get @Home?" and enter your address to see if the service is
available in your area. If it's not yet available in your neighborhood, @Home
will contact you when it is.
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