 (AAL) protocols if the carriage of each service is to be across the interfaces. Any number of signalling circuits can be Bibliography 44/17 Class A Class B Class C Class D Timing relation between Required Not required source and destination Bit rate Constant Variable Connection mode Connection-oriented Connection- Figure 44.16 Service classification for adaption layer established. These Signalling Virtual Channels (SVC) are identified exploring not only the technology but the new broadband services by Signalling Virtual Channel Identifiers (SVCI) and are only and applications that will be required by users. Specification work assigned when required. To assign, check and remove these SVC a is progressing very quickly and it is expected that pilot broadband meta-signalling protocol has been defined which is carried in a networks conforming to international standards will begin to meta-signalling virtual circuit with a predefined VCI and which is emerge towards the end of the decade. always present. Discussions are still proceeding on the specification of the signall- ing protocols. A short term solution may be to base these on the 44.9 Bibliography narrowband ISDN signalling protocols defined in 1.450/1 (Q.930/1), however a longer term solution may to define a new signalling protocols suitable for use both in the access network and Bonnati, Casali and Popple (1991) Integrated Broadhand Com- main network. munications: Views from RACE, North Holland. CCITT (1988) Blue Book - Fascicle III.7 to 11.9, CCITT/ITU. 44.8.6 Broadband standards Clark, M.P. (1991) Networks and Telecoms, Wiley. Griffiths, J.M. (1990) ISDN Explained, Wiley. The standards and specifications for a broadband ISDN are now Griffiths, J.M. (1986) Local Telecommunications 2 Into the digital beginning to emerge. In Europe the European Commission is assist- era, Peter Peregrinus Ltd. ing this process through its RACE programme. The RACE pro- Marsden, B.W. (1988) Communication Network Protocols, Char- gramme began in 1988 with 50% funding of some 50 coll