r use just one media, but the end users can add and drop different media within one session. These new services will enable the users to communicate and interact in innovative ways, to save money, time, trouble and have fun. For the operator, the key issue is to launch a wide variety of services cost-efficiently by using a single connectivity mechanism that also provides centralised charging. This is possible with the IP multimedia core. 3GPP Release 4 Circuit Core Network IN/SCE PSTN/ISDN Gateway BICC CS-2 (SIP-T) Control Server H.248 H.248 Other PLMN Iu-CS IP/ATM Backbone WCDMA Figure 4.10 MSC server network architecture 4.4 3GPP Release 4 Circuit Core Network 4.4.1 Release 4 Core Network Architecture Figure 4.10 presents one soft-switch solution implementation of the 3GPP release 4 architecture. The user plane and the control plane are separated in the MSC server concept. This reflects the split architecture as defined in the 3GPP specification TS 23.205. The separation of the two planes in the core network means that 2G/3G MSC functionalities evolve such that user plane traffic switching functions are performed by the media gateway network element, while call control and mobility management functions are performed by MSS/GCS network elements. The MSS/GCS network elements also take care of the connection of media channels in the MGW. 3GPP release 4 circuit core standards recommend BICC-CS2 as the signalling protocol in the Nc interface to be used to establish bearer channels for user plane connections both with an ATM and IP based backbone. Furthermore, BICC-CS2 is independent from the signalling message transport layers, which means that it may be carried on top of the TDM (SS7), ATM (SAAL) or IP (SIGTRAN). The H.248 (MEGACO) Protocol is used by the MSS to control the MGWs when routing user plane traffic through different bearer channels in the backbone. When the backbone network is based on IP transport, the signalling for call control between MSS/GCS elements in the release 4 core circuit network can be bas