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Unit 6: Business Networks and Telecommunications

telephone network, but this is expensive and relatively poor for large volumes of data Notes
transmission.

Figure 6.14

Wide Area Network (WAN) is a telecommunication network which covers a large geographical
area, and uses communications circuits to connect the intermediate nodes. A wide area network
spans a wide geographical area such as a state or country. Numerous WANs have been constructed,
including public packet networks, large corporate networks, military networks, banking
networks, stock brokerage networks, and airline reservation networks. WANs are used for
many different purposes. Some are designed as a communications backbone for a large distributed
organisation. Other WANs focus on particular transaction packages. Many WANs are used to
transfer and consolidate corporate data, such as daily transaction summaries from branches.
Some WANs are very extensive, spanning the globe, but most do not provide true global
coverage. A major factor which influences WAN design and performance is the requirement of
lease communications circuits from telephone companies or other communications carriers.
Transmission rates are typically 2 Mbps, 34 Mbps, 45 Mbps, 155 Mbps, 625 Mbps or sometimes
even more.

Wide area networks are often implemented in the form of a Virtual Private Network (VPN) a
private network configured within a public network. Telephone companies have provided non-
switched-leased lines for decades by dedicating portions of their high - capacity trunk lines to
links between specific company sites. VPNs go a step further by supporting communication to
any point within the private network but not supporting communication outside. This type of
VPN service costs more than a pure leased line approach, but a telephone company manages the
network. Today, there is tremendous interest in building VPNs that use the Internet to provide
a secure and encrypted connection between two points. These VPNs are run by Internet Service
Providers (ISPs), who are responsible for maintaining bandwidth, network availability, and
security.
WANs can link to workstations or terminals through LANs. The LANs perform local data
processing, and they link to the WAN for data needed or provided beyond the local environment.
An example of this approach is the long-term direction of Apollo, the United Airlines reservation
system. In this system, LANs are gradually being installed at travel agencies to replace dumb
terminals linked to midrange computers and mainframes. The LANs maintain local copies of
reservation data. New reservations are uploaded through the WAN, and travel data is downloaded
to the LANs. With this arrangement, agents who are booking reservations at travel agencies can
keep working even if the WAN or one of the central computers is down.

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