company verifies that a twisted pair copper line is available for the location; the DSL
provider installs the inside wiring to your PC; and the ISP provides the Internet service. If
you buy your DSL from the ILEC, you are dealing with a single entity, but the price may
be higher and the installation time longer—DSL is not the ILEC’s primary business. Most
DSL providers do not sell directly to consumers and use ISPs to resell their services. In
these cases, the ILEC still must do its part, but the other companies provide the DSL and
Internet. This arrangement results in faster installations and in most cases, lower prices.
Many areas now have a technology called “line-sharing” that allows you to use a
single phone line for both voice (telephone) and data (DSL). This results in much lower
costs, since a second phone line is no longer required and relatively instantaneous instal-
lations are available.DSL Modems, Bridges, and Routers
Most home users who use DSL subscribe to ADSL (asymmetrical DSL), which transmits
and sends at different speeds. The customer premise equipment (CPE) for ADSL service
is typically an external DSL modem, or bridge, that is attached to a PC through a twisted
pair cable and an RJ-45 connector into a NIC installed in the PC. The NIC, the cable, and
the connector are the same as would be used for a PC on a LAN. The DSL modem bridges
the data from the phone line to a format usable by the NIC and PC. The DSL modem can
also be an internal card that is installed in a PCI slot inside the PC. An internal DSL
modem does not require a NIC.
SDSL (symmetrical DSL), which sends and receives at the same speed, is usually used
to connect a network to DSL and uses a router as its CPE. ADSL service can also be con-
nected through a router, but in most cases the bandwidth is not sufficient for this purpose.
A router allows several PCs to share the DSL bandwidth.Cable Modems
Another way to access the Internet is through a cable modem connection using the cable
TV system that most likely already is connected to your home. Cable service is similar to
ADSL service, in that it provides higher download speeds and lower upload speeds. Cable
Internet access uses a modem, usually an external device, that connects the PC to the cable
lines that carry the signal back to what is called the cable head-end where it connects to
the Internet.
The real benefit of a cable modem is that you can get high-speed Internet access and
kee pyour phone line free—and you can still watch TV while you are surfing the Net. It is
very rare to find a cable company that does not also require you to subscribe to cable TV
service to also get the cable Internet service. A device called a signal splitter that is sup-
plied by the cable company separates the two signals. The bad news about cable Internet
service is that the cable system is a shared system, and when there is heavy cable TV
demand, it can impact the speed of Internet data. However, in most cases, the bandwidth
is high enough to offset for slow-down on the system.Chapter 20: Networks and Communications^533