dditional functions Figure 14.11 MSC server functions, example The GMSC and TSC server functionality is often housed in the MSC server. 14.5.3 TELEPHONY SERVER IN FIXED NETWORKS The telephony server (TeS) functional component handles circuit-oriented calls, for example call signalling, call routing and termination, maintenance of relevant call state, event handling and the invocation of network services. TeS might control ATM as well as IP connectivity networks. See Figure 14.12. 14.5.4 SIGNALLING INTERFACES For PSTN/ISDN subscribers a subscriber loop signalling system between a user terminal and the edge node is common. See Figure 14.3. Telephony server upgraded and re-used H.248 H.248 H.248 H.248 network network H.245 MGW upgraded and re-used Figure 14.12 A BICC protocol combined with ATM and later IP connectivity Understanding Changing Telecommunications - Building a Successful Telecom Business Signalling system No 7 (SS7) is a well-known four-level connectionless signalling sys- tem, primarily used for control of inter-exchange voice traffic. Seen from the evolving core network SS7 will often appear as an access technology until the MGW has 'conquered' the present local nodes. Q.931 is the ISDN network layer signalling protocol. The V5 interface is used between an access node and the local exchange. V5.1 interface is based on a static multiplexer type principle in which a single E1 link is used to carry the bearer channels and the signalling channels. The bearer channel allocation to the V5.1 subscriber is fixed. The V5.2 interface is based on a dynamic concentrator type principle, typically consisting of 1 to 16 E1 links carrying bearer and signalling channels. The bearer channel allocation to the subscriber is dynamic on a per call basis. 14.5.5 BICC AND BICC IP BEARER CONTROL PROTOCOL IPBCP BICC is a signalling protocol based on ISUP. The basic issue leading to the develop- ment of BICC was that network operators had experienced heavy growth of their voice traffic mainly due to the Internet. PSTN/ISDN netw