for all services previously provided by the CS domain. Here we retain the PS domain but phase out the CS domain. Whether the latter can be achieved in its integrity including all security aspects remains to be seen, since it is still under standardization or technical specification. 9.1.3 The All IP and Service Evolution As noted in Chapter 1, the widespread usage of Internet and IP's ability to communicate between different networks has made IP a convergence layer to evolve from a simple data platform to larger structure for services. By aiming to reach further than the circuit switch, IP now leads mobile communications to new dimensions. The IP protocol has opened up a whole range of wireless applications, which will allow service providers and operators to develop totally new and innovative services while enhancing their existing infrastructures. Thus, the main drivers for IP services include a full range of new multimedia applications beside IP telephony. 9.1.3.1 Transition to All IP Services Passing to ALL IP multimedia services will take some time; therefore both classical CS mobile services and IP multimedia services will co-exist concurrently. As a result, net- Towards IP Based Networks works will have to support traditional CS services and new PS services such as multi- media with the variety of terminals these services will bring in order to offer seamless roaming between evolving 2G networks and optimized 3G networks. This means that Release 2000 (now broken up into R4 and R5) will need to support service offerings while remaining independent from transport technology. The ROO platform will have to support at least the following [2]: hybrid architecture network evolution path new capabilities IP based call control real-time (including voice) services over IP with end-to-end QoS GERAN (support for GMS/EDGE Radio Access Network) services provided using toolkits (e.g. CAMEL, MExE, SAT, VHE/OSA) backwards compatibility with Release 99 services no degradation in QoS, security, authentication, privacy suppor