Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

112 CHAPTER 7 Wide Area Networking
INTERNET ACCESS METHODS
In this section, we will look at Internet access technologies such as digital subscriber
line (DSL), cable, Plain Old Telephone Service (POTS)/public switched
telephone network (PSTN), satellites, and wireless.
Digital Subscriber Line
DSL is commonly denoted as xDSL, where the x specifies what type of DSL is
in use. DSL is commonly used to access the Internet from both residential and
business locations to provide high-speed access to the Internet. DSL became very
popular as dial-up technologies become increasingly unable to meet the demand
for fast access to the Internet.
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DSL and other high-speed technologies are slowly displacing dial-up service
to the Internet. DSL is one of the most highly used because it can use
preexisting phone lines in your home, so installation is a bit cheaper and
less intrusive.
DSL is not a shared medium, unlike cable networks, which use shared access.
Shared access means that when there is heavy usage of the system, less
bandwidth is available to individual users. DSL has dedicated bandwidth,
so the only one using that bandwidth is you.
DID YOU KNOW
One drawback of DSL, however, is that the QoS is dependent on the user’s distance from
the central office (CO).The CO is where the network endpoint is located and is generally
run by your Internet service provider (ISP). The farther you are from the CO, the slower the
service is. There are many forms of DSL. The most common forms of DSL are asymmetric
DSL (ADSL) and symmetric DSL (SDSL).
ASYMMETRIC DSL
ADSL is the most widely deployed form of DSL technology. Most homes and
small businesses currently using DSL technology use ADSL. Characteristics of
ADSL are as follows:
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ADSL is used to transmit digital information on preexisting phone lines.
Unlike dial-up, ADSL provides an always on connection to the Internet.
ADSL is able to place voice and data information on the same line.
ADSL is asymmetric. This means that ADSL is designed to provide more
bandwidth in one direction than in the other.
ADSL generates downstream speeds of about 8 Mbps and upstream speeds
of up to 640 Kbps.
SYMMETRIC DSL
SDSL is typically used in larger companies, and the upstream and downstream
channels have the same size; that is, the download speed and upload speed are
equal. SDSL operates at about 2 to 2.5 Mbps.