col for the packet network and can establish and remove bearer connections over the packet network. The CSF handles the call signalling, that is, ISUP signalling to the Control Network M = Media gateway M3UA, SCTP see section 14.9.2 R = Router LE = Local exchange BICC/M3UA/SCTP/IP IPBCP Mobile systems: H.248/SCTP/IP/(MPLS) GCP and ISUP over ISUP/RTP/UDP/IP/(MPLS) M3UA/SCTP/IP/(MPLS) network Circuit Emulation Circuit Emulation voice/RTP/UDP/IP/MPLS IPBCP to set up a bearer between MGWs IPBCP is tunneled through H.248 and BICC Figure 14.13 Example of signaling protocols and signalling and voice transport in an IP core as defined in Figure 14.12 PSTN/ISDN network and BICC signalling in the BICC network. The call mediation node (CMN) can be used to route the BICC messages and may be useful in a large-scale BICC network with a large number of ISNs. Two other nodes have also been defined for the BICC architecture: the transit serving node (TSN) and the gateway serving node (GSN) The TSN is a node that handles BICC on both sides. A TSN may be used to offer intelligent network based services. A TSN may also convert the bearer from one type of packet network to another. The GSN is similar to the TSN since it also handles BICC on both sides. A GSN acts as a gateway between network operators in a full BICC environment. BICC IP Bearer Control Protocol (IPBCP) (ITU Q. .1970) is used for the exchange media stream characteristics, port numbers, and IP addresses of the source and destination of a media stream to establish and allow the modification of IP bearers. The information exchanged with IPBCP is done during BICC call establishment. In addition it may be exchanged after a call has been established. IPBCP uses the Session Description Protocol (SDP) defined in RFC 2327 to encode this information. See Figure 14.13. Section 15.8 describes the similar PDP context. Signalling transport is described in section 14.9.2. 14.6 PACKET MODE DOMAIN The packet mode domain is introduced in GPRS and it is conveyed into UMTS. In the IMS pha