tailieunhanh - Mạng và viễn thông P40

Technical Standards for Networks In the past, telecommunications networks have been evolved in the minds of their designers to meet well defined but changing user demands. These broadly innovative influences are bound to persist and users can look forward toever more sophisticated telecommunications services in the future. Itwas onlyin themid-1960s that customer-dialled international telephone callsfirst became possible, and in those days such calls were for therich alone. | 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 40 Technical Standards for Networks In the past telecommunications networks have been evolved in the minds of their designers to meet well defined but changing user demands. These broadly innovative influences are bound to persist and users can look forward to ever more sophisticated telecommunications services in the future. It was only in the mid-1960s that customer-dialled international telephone calls first became possible and in those days such calls were for the rich alone. Nowadays the advance of technology has made them so much cheaper that everyone takes them for granted. In the late 1960s everyone marvelled at the first live satellite broadcasts now there are so many satellites in space that many of them no longer have names only longitudinal geographic location references. Every day the world s communicators move larger and larger volumes of video text speech and data information around the globe and all without a second thought. The revolution in communications that we have seen and the ever-widening scope for information transfer have only come about through an almost fanatical emphasis on the international compatibility of telecommunications networks and equipment underpinned by worldwide agreement on the technical standards without which interconnection between networks in different countries and the interworking of different network types would be impossible. This chapter discusses the various bodies involved in setting these standards. It outlines in particular the recommendations of ITU International Telecommunications Union the world s most authoritative body on telecommunications technical standards. THE NEED FOR STANDARDS Whenever two or more pieces of equipment built by different people or different manufacturing companies are called on to work harmoniously .