he session. See also the signalling plan in Chapter 8. Understanding Changing Telecommunications - Building a Successful Telecom Business 14.5 CIRCUIT MODE DOMAIN The circuit domain embraces mobile and fixed networks mainly intended for voice. The typical circuit mode feature is the functions of the servers, whereas the traffic path normally migrates to become packet based. Data traffic can manage with the connectivity layer. See Figure 14.10. Let us start with the mobile servers, which are called MSC and TSC/GMSC (TSC = transit switching centre). 14.5.1 MSC SERVER The MSC server remotely controls the circuit-switched part of the MGW and initiates set-up/release via the gateway for the user plane. The control is supported by the gateway control protocol (GCP, H 248). When needed, the MSC server connects devices to the payload path (e.g. codecs, tone senders). Figure 14.11 gives an overview. The MSC server also supports the radio access network application part (RANAP) for control signalling over the RNC-MSC interface, SO that radio access bearers can be established and released. 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 A