Sách Local Area Networks (LANs)

We have seen how packet switching has contributed greatly to the efficiency and flexibility of
‘wide area’ data networks, involving a large number of devices spread at geographically diverse
locations. Packet switching, however, is not so efficient for smaller scale networks, those limited
to linking personal computers within an office building; that is the realm of an alternative type of
packet-switched-like network called a local area network or LAN for short. In this chapter we
discuss the concept of a LAN and the various technical realizations which are available.

19.1 THE EMERGENCE OF LANs
LANs emerged in the late 1980s as the most important means of conveying data between
different computers and computer peripheral devices (printer, file server, electronic mail
server, fax gateway, host gateway, computer printer, scanner, etc.) within a single office,
office building or small campus. LANs are constrained by their mode of operation to a
geographically limited area, but are ideally suited for short distance data transport.
A high bit speed LAN can carry high volumes of data with rapid response times.
Such performance is crucial for most office applications, and has made them the ideal
foundation for the new generation of ‘electronic offices’ comprising electronic work-
stations, word processors, shared printers, electronic filing cabinets, electronic mail
systems and so on.
Most LANs conform to one of the different types specified in the Institution of
Electrical and Electronic Engineers’ IEEE 802 series of standards. All the types have
been developed from proprietary LANs, developed earlier by individual companies or
organizations, but have now achieved American and worldwide recognition, as IS0
8802 standards.



Chapter 19 copy