Hardware Reference
In-Depth Information
On the other hand,
asymmetric
means unequal. With an asymmetric DSL connection,
the upload speed is slower than the download speed. An ADSL connection may download
at 12 Mbps but upload at only 1.8 Mbps, for example. For most people this is acceptable
because the volume of data is much higher coming to them than going from them.
ADSL service is typically much less expensive than SDSL, and it works fi ne for most
users. People who need high-speed uploading, though, such as someone who is running an
Internet fi le-sharing service, may fi nd it worthwhile to pay extra for SDSL service.
DSL service requires a telephone line, of course. You also need a DSL terminal adapter
(modem). Some service providers distribute a box that is a combination of a DSL modem and
a router (wired or wireless) for sharing the DSL connection with multiple computers. Others
provide just a basic DSL terminal adapter, and you must provide your own router if you
want to share its connection. You may also need a splitter, or a micro fi lter, to separate the
analog telephone signal from the digital Internet signal, both passing through the same lines.
Cable
Cable Internet service uses the unused bandwidth on the same cables that carry your TV
signal. Cable service in many areas is faster than DSL, but it's a shared pipeline. So if your
neighbors are also heavy Internet users, you may experience a slowing down of your service
at peak usage times. Cable Internet service is symmetric, so upload and download speeds are
approximately the same, unless your cable company intentionally throttles upload speeds
(for example, to discourage users from running high-traffi c servers from their homes).
To get Internet from your cable TV provider, you'll need a cable modem. The providers
typically lease these to you, so you don't have to buy your own and worry about
obsolescence a few years down the road. A cable modem accepts input from a coaxial
cable from the wall, the same kind of cable that brings in your TV programming. It has an
RJ-45 output jack, just like that for an Ethernet cable, which then can be connected to a
broadband router (wired or wireless) to share the cable Internet connection with multiple
computers in your home or offi ce.
Satellite
Satellite Internet service isn't as fast or as effi cient as cable or DSL, but it's more widely
available. Whereas cable service requires you to be within the service area of your
cable company, and DSL connections are limited to within a few miles of the telephone
company's central offi ce, satellite Internet can be picked up anywhere that has a clear view
of the southern sky. Satellite service is asymmetric, like ADSL; you may have a download
speed of 1.5 Mbps and an upload speed of 256 Kbps, for example.
Satellite Internet requires a special satellite dish, similar to the ones used for satellite TV,
but with a transmitter on it. (Ordinary satellite dishes are receive-only.) Two cables run
from the dish to your residence—one for input and one for output. These cables connect
to a satellite terminal adapter (modem), which then connects either directly to a PC or to a
broadband router to share the connection.
Satellite service is more susceptible to harsh weather conditions, and it may cut out
during rain or snowstorms. It's also slower and more expensive per month than cable or
DSL, and you usually have to buy all the equipment up front, rather than lease it.
