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Signalling System Noe 7 TheITU-Tsignallingsystemnumber7, SS number7,SS7,CCITT7,C7 or numberseven signalling system is the most recently developed of telephone network signalling systems. It is already widely deployed in digital telephone networks and ISDNs across the world, and also will be a ‘cornerstone’ of ‘intelligent networks’ and broadband ISDNs (B-ISDN). | 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 12 Signalling System No. 7 The ITU-T signalling system number 7 SS number 7 SS7 CCITT7 C7 or number seven signalling system is the most recently developed of telephone network signalling systems. It is already widely deployed in digital telephone networks and ISDNs across the world and will also be a cornerstone of intelligent networks and broadband ISDNs B-ISDN . It is a complex common channel signalling system which enables the controlling processors of two digital exchanges or databases to communicate directly and interact with one another in a manner optimized for digital transmission media. SS7 has also formed the basis of a number of further-developed regional signalling systems. In the United States for example ANSI SS7 is a derivative while the UK national version is C7 BT . This chapter describes the overall structure and capabilities of SS7. SS7 SIGNALLING BETWEEN EXCHANGES The SS7 signalling system is described in the series of ITU-T recommendations. A common channel signalling system optimized for digital networks it allows direct transfer of call information transfer between exchange processors. Comprising a number of layered and modular parts each with a different function it is a powerful general-purpose signalling system capable of supporting a range of applications and administrative functions including ISDN integrated services digital network intelligent networks INs mobile services . cellular radio network administration operation and management 249 250 SIGNALLING SYSTEM NO. 7 In addition its modular nature lends itself to the development of new user parts which may be designed to support almost any new service that can be conceived. The user parts of the system that have been developed so far are MTP message transfer part SCCP signalling connection and .