Internet Access (WAN) Links
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The Internet also happens to use a huge number of WAN links. All of those lines connecting
an enterprise or home to one of the ISPs in Figure 3-13 represent some kind of WAN
link that uses a cable, while the phones create their WAN link using wireless technology.
These links usually go by the name Internet access link.
Historically, businesses tend to use one set of WAN technologies as Internet access links,
while home-based consumers use others. Businesses often use leased lines, connecting a router
at the business to a router at the ISP. The top of Figure 3-14 shows just such an example.
Figure 3-14 Three Examples of Internet Access Links
Consumers often use technologies like DSL and cable for Internet access links. These technologies
use cabling that is already installed in most homes, making these services somewhat
inexpensive for home users. DSL uses the analog phone lines that are already installed in
homes, while cable Internet uses the cable TV (CATV) cable.
NOTE While DSL and cable are popular with consumers, many businesses use these
technologies for Internet access.
All three of the Internet access technologies in Figure 3-14 happen to use a pair of routers:
one at the customer side of the WAN link and one at the ISP side. The routers will continue
to think about network layer logic, of sending IP packets to their destination by forwarding
the packets to the next router. However, the physical and data link layer details on the
WAN link differ as compared to leased lines. The next few pages examine both DSL and
cable Internet to show some of those differences.