A WAN is a data communications network
that covers a relatively broad geographic area, often using
transmission facilities generally provided by service providers and
telephone companies. Unlike LANs, a WAN connection is usually rented
from the service provider. As shown in the Figure ,
WANs are used to connect various sites at different
geographic regions so people at each site can exchange information.
The connection requirements vary
considerably. For example, two sites may require a dedicated
connection because they most often exchange real-time data. On the other
hand, a mobile user may need to connect to a site only to
periodically check e-mail throughout the day.
A network administrator building a remote
network must weigh such issues as user needs, bandwidth
requirements, and costs of the various technologies.
The
network administrator must then select the technologies that best
suit the corporation’s needs and budget.
As illustrated in Figure ,
the variety of WAN connection types offered by service providers can
be grouped into the following categories:
- Dedicated connectivity (leased
lines)
- Circuit-switched networks
- Packet-switched networks
Dedicated lines have point-to-point
connections that are indefinitely reserved for transmissions, rather
than being switched as transmission is required. Typically, a
dedicated connection is made using serial lines. Circuit-switched
connections are physical circuit paths that are only established
during the duration of a call. Once the circuit is formed, all data
travels the same path. Physical circuit-switched examples
include asynchronous serial and Integrated Services Digital Network
(ISDN). Packet-switched networks use packet-switching technology for
data transfer. This means that the data is divided into separate
packets. The packets include sequence numbers and a destination
address. The packets can travel different paths and are reassembled
at the destination. Frame Relay uses packet-switching technology.
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