nsport technologies, i.e. IP, ATM or TDM. This flexibility enables operators to maintain a common backbone technology for their CS and PS services. Packet switched (PS) traffic is expected to increase in release 4 networks and later in release 5 networks, thus ensuring a common backbone with greater synergies: IP, ATM or TDM. The separation of user and control plane architecture anticipates the evolution to an all-IP architecture, which at the same time supports the already existing networks. This enables operators to reduce operating expenditure (OPEX) with the MSS system compared to a similar network in a TDM network environment, due to high capacity compact network elements and a common network backbone. The number of required network elements and sites is expected to be lower as a result of this common circuit switched network for both GSM and UMTS networks. The 3GPP release 4 network contains an additional element called the IP multimedia subsystem (IMS). The IMS, when fully specified, will contain a uniform way to maintain VoIP calls, thus offering the oper- ators a way to deliver VoIP calls between UMTS networks. In addition to 'universal VoIP' the IMS offers a platform to other real-time and non-real-time IP services, such as, for instance, multimedia services. The IMS consists of the media gateway control function (MGCF), the call state control function (CSCF) and the media resource function (MRF). These three functionalities form an extended model of connection management when compared to the 3GPP release 99 network. Basically the MGCF controls the MGW used in the connections, whether when using conversions, echo cancelling, etc. The CSCF and MRF together form the logic of how the transaction using IMS is treated. The MGCF-CSCF-MRF model brings a big and new aspect to the system, which is related to the services, their creation and treatment. The 3GPP release 4 network contains a service platform, which is taken into use through the MGCF-CSCF-M chain. The basic concept exists in the 3GPP release 99 netw