When the
customer is not using the full bandwidth on its virtual circuit, the carrier, through statistical
multiplexing, can make that unused bandwidth available to another customer. Figure 5-8
shows an example of virtual circuits through a packet-switched network.
Figure 5-8 Packet Switching
CSU/DSU
CSU/DSU
DSU/CSU
VC
Synchronous
Serial
Synchronous
Serial
358 Chapter 5: WAN Connections
Digital Subscriber Line
DSL technology is an always-on connection technology that uses existing twisted-pair
telephone lines to transport high-bandwidth data and provides IP services to subscribers. A
DSL modem converts an Ethernet signal from users to a DSL signal to the CO. Figure 5-9
shows an example of DSL connectivity from a remote site through a service provider.
Figure 5-9 DSL Connectivity
DSL technology allows a service provider to offer high-speed network services, up to and
exceeding the speed of a T1 connection, to customers, using installed local-loop copper
lines. DSL technology allows the local-loop line to be used for normal telephone voice
connection, plus an always-on connection for instant network connectivity. Multiple DSL
are multiplexed into a single, high-capacity link by the use of a DSL access multiplexer
(DSLAM) at the provider location.
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