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Frame Relay For datatransfer, X.25-based packet switching has established itself worldwide as a standard and very reliable means. However, X.25 is not a technique suited to the higher quality and speeds of so by modern data communications networks, and it is beginning to be supplanted new techniques, among them ‘frame relay’. In this chapter we start by discussing the shortcomings of X.25-based packet switching in carrying highspeed bitrates and explain how frame relay was designed to overcome these problems | 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 20 Frame Relay For data transfer X.25-based packet switching has established itself worldwide as a standard and very reliable means. However X.25 is not a technique suited to the higher quality and speeds of modern data communications networks and so it is beginning to be supplanted by new techniques among them frame relay . In this chapter we start by discussing the shortcomings of X.25-based packet switching in carrying highspeed bitrates and explain how frame relay was designed to overcome these problems. We conclude with a more detailed review of the frame relay protocols themselves. 20.1 THE THROUGHPUT LIMITATIONS OF X.25 PACKET SWITCHING The reliability of X.25 packet switching has resulted from worldwide accepted standards and the huge availability of compatible hardware and software products enabling computer devices made by different manufacturers and strewn around the world to intercommunicate without difficulty. X.25 was the first universal data communication protocol and it stimulated rapid growth in data communication traffic volumes because of its reliability and its robustness. Paradoxically its robustness is now leading to the demise of X.25 because one of the main limitations of packet switching based on X.25 is its unsuitability for carriage of high speed information channels and its relative inefficiency when used in conjunction with high quality transmission networks. When X.25 was developed in the late 1970s the relative speed of the communicating devices was very low in comparison with today s devices typically under 9600 bit s and the quality of wide area digital lines was comparatively poor. As a result and to their credit X.25 packet networks are highly robust against poor line quality. X.25 networks are able to survive and even recover from even extensive bit .