tailieunhanh - Mạng và viễn thông P19

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 computerswithin 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. . | Networks and Telecommunications Design and Operation Second Edition. Martin P. Clark Copyright 1991 1997 John Wiley Sons Ltd ISBNs 0-471-97346-7 Hardback 0-470-84158-3 Electronic 19 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. 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 workstations 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 ISO 8802 standards. LAN TOPOLOGIES AND STANDARDS The different types of LAN are .