CCITI’ began the specification of the second-generation common-channel signaling system, known as signaling system (SS7), in the mid-1970s. The system was developed initially for telephony call control, and the first recommendations were published in the CCITT Yellow Books of 1981. During the past decade, the applications of SS7 applications have expanded, and now also include call control in the integrated services digital network (ISDN), and operations in the network that aeennot related to individual trunks. Most of this work has been published in the CCITT Blue Books of 1989. More recent additions have been issued as individual International Telecommunications. | Signaling in Telecommunication Networks. John G. van Bosse Copyright 1998 John Wiley Sons Inc. ISBNs 0-471-57377-9 Hardback 0-471-22415-4 Electronic INTRODUCTION TO SIGNALING SYSTEM NO. 7 CCITT began the specification of the second-generation common-channel signaling system known as signaling system SS7 in the mid-1970s. The system was developed initially for telephony call control and the first recommendations were published in the CCITT Yellow Books of 1981. During the past decade the applications of SS7 applications have expanded and now also include call control in the integrated services digital network ISDN and operations in the network that aeennot related to individual trunks. Most of this work has been published in the CCITT Blue Books of 1989. More recent additions have been issued as individual International Telecommunications Union ITU Recommendations. CCITT and CCIS were used only in the international network and in the AT T long-distance network. The objective for SS7 was to develop a signaling system that can be used worldwide. However this objective has not been met completely. Several national versions have been defined notably a version specified by American National Standards Institute ANSI and Bellcore Bell Communications Research for the . networks and British Telecom s national user part NUP for the network in the . In what follows we speak of SS7 when discussing the general aspects of the system that essentially apply to all versions and refer to the CCITT-defined system as CCITT No. 7 and to the North American version as ANSI No. 7. SS7 Signaling Links. The signaling links are carried on the digital transmission channels that were developed in the 1960s for digital PCM trunks. In the . these signaling links generally transmit at 56 kb s. In most other countries the transmission is at 64 kb s 1 . 150 SS7 STRUCTURE 151 These bit rates greatly exceed the 2400-4800 bits s rate of SS6 signaling links. SS7 call-control messages
