ignal messages. tures and access capabilities, Recomms. I. 412. CCITT (1988h) Basic user-network interface, Recomms. I. 430. 43.3.3 User-to-user signalling CCITT (1988i) Primary rate user-network interface, Recomms. I. CCITT (1988j) Digital access signalling system, data link layer, This facility may be used to exchange information between two Blue Book, Vol. VI Fasc. VI.10, Recomms. Q921, ITU, Geneva. N-ISDN users, the information transferred being, for example, data CCITT (1988k) Digital access signalling system, network layer, or keypad/display. The user-to-user signalling may be performed: Recomms. Q931. Dahlbom, C.A. (1972) Common channel signalling, - a new flex- Over the circuit switched B traffic path connection between the ible interoffice signalling technique, IEEE International Switch- two users. ing Symposium Record, Boston, U.S.A. 2. Over an end-to-end signalling connection between the two Miller, C.B. and Murray, W.J. (1971) Trunk transit network signall- users (Figure 43.8). ing systems - multifrequency interregister signalling, Post Off. Electr. Eng. J., 63 Pt.1. 43-48. The user-to-user information is carried transparently, and is not Welch, S. (1979) Signalling in Telecommunications Networks, IEE interpreted, by the network. Telecommunications Series 6, Peter Peregrinus Ltd., London. This page intentionally left blank The Integrated Services Digital Network Richard A Boulter BSc (Hons) CEng FIEE Contents Introduction 44/3 International standards for ISDN 44/3 ISDN services aspects 44/3 Network aspects 44/5 User/network interfaces 44/6 ISDN developments in the U.K. 44/10 ISDN applications 44/13 Broadband ISDN 44/13 44.9 Bibliography 44/17 This page intentionally left blank Introduction 44/3 44.1 Introduction These facilities have been provided in order to support telephony in the most economical way possible. They have, however, set the The main features of any network can be categorised into the scene for the development of what has become known as the ISDN, transmission, switching, signalling an