leased. The MSC server also supports MAP signalling to the HLR and equipment identity register (EIR). Furthermore, the ISDN and bearer-independent call control (BICC) protocols can be used for control signalling between the call-control servers in the circuit-switched domain and external integrated services digital networks. 14.5.2 TSC/GMSC SERVER The circuit mode PLMN traffic often has PSTN/ISDN as the originating or terminating point. The TSC/GMSC server selects the path across the core network and suitable MGWs with suitable gateway facilities. IP connectivity, UMTS originating call Network control layer server server Q.BICC RANAP server N-ISUP External WCDMA RAN (ATM based) networks (TDM based) ATM VCC CR-LDP CR-LDP MGW & H.245 MGW & IP transport Signalling User plane Connectivity layer Figure 14.10 A circuit mode control domain with IP/MPLS transport Control Network Control Connection management Mobility management Security Charging server Additional 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 co