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Asynchronous Transfer M o d e ( ATM) ATM looks set to become the first universal telecommunication technology, capable of switching and transporting all types of telecommunication connection (. voice,data video, multimedia). It willformthebasisofthefuture broadbandintegratedservicesdigitalnetwork(B-ISDN). Because of the anticipated importance of ATM, wediscussherethetechnicalprinciples and terminology in depth, defining the main jargon and explaining what marks out ATM from its predecessors. In particular, discuss the principlesof statistical multiplexing and the specifics of we cell switching. . | 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 26 Asynchronous Transfer Mode A TM ATM looks set to become the first universal telecommunication technology capable of switching and transporting all types of telecommunication connection . voice data video multimedia . It will form the basis of the future broadband integrated services digital network B-ISDN . Because of the anticipated importance of ATM we discuss here the technical principles and terminology in depth defining the main jargon and explaining what marks out ATM from its predecessors. In particular we discuss the principles of statistical multiplexing and the specifics of cell switching. A FLEXIBLE TRANSMISSION MEDIUM An ATM-equipped transmission line or telecommunication network is able to support usage by multiple users simultaneously different telecommunication needs . telephone data transmission LAN interconnection videotransmission etc. each application running at different transmission speeds . with differing bandwidth needs However these capabilities are also offered by predecessor technologies so why bother with ATM you might ask What distinguishes ATM from its predecessors is that it performs these functions more efficiently. ATM is capable of an instant-by-instant adjustment in the allocation of the available network capacity between the various users competing for its use. Rather than allocating fixed capacity between the two communicating parties for the duration of a call or session ATM ensures that the line capacity is optimally used on a moment-by-moment basis by carrying only the needed or useful information. 451 452 ASYNCHRONOUS TRANSFER MODE ATM The dynamic allocation of bandwidth is achieved by ATM using a newly developed technique called cell relay switching. Understanding its principles is the key to understanding ATM its strengths and .