fly highlight the key elements of IMS: Call State Control Function (CSCF): It manages the IP multimedia sessions by using the SIP protocol and also acts as SIP server. Media Gateway Control Function (MGCF): It is responsible for signaling between the packet switched domain and circuit switched networks (for example, PSTN). Breakout Gateway Control Function (BGCF): It selects to which PSTN a session should be forwarded. It then forwards the signaling to the appropriate MGCF and BGCF in the destination PSTN network. IP Multimedia Media Gateway (IM-MGW): It performs media translation, that is, trans- lation between media signals encoded in one format on one side and signals encoded in another format on the other side. Multimedia Resource Function (MRF): It is split into MRFC (MRF Controller) and MRFP (MRF Processor). The MRFC controls the media stream resources of the MRFP, which processes and mixes the actual media streams. Home Subscribed Services (HSS): It is a database that stores subscription and location information. It can be thought of as an enhanced version of the home location register found in GSM. Core Networks and Operations Support Systems External Internal Network Content Packet Provider / Multicast Network, Broadcast Source Internet External Gn/Gp Content UTRAN BM SC Provider / Multicast Broadcast Source lu / Gb GERAN Core Network Figure 8.4 3GPP Release 6 core network architecture. Reproduced with permission from ETSI [9] 8.2.1.4 Release 6 3GPP Release 6 enables HSUPA (High Speed Uplink Packet Access) and was functionally frozen in March 2005. In Rel-6 HSUPA supports peak data rate of 5.76 Mbps. In Release 6 a new functional node is added in the CN to support MBMS (Multimedia Broadcast Multicast Service) for TV service. The node, BM-SC (the Broadcast-Multicast Service Center) provides functions for MBMS user service provisioning and delivery. BM-SC: It serves as an entry point for PLMN-internal and external MBMS Content Providers, where it is used to authorize and initiate MBMS Bearer Services withi