ork and actually the service capabilities are presented there, but in the 3GPP release 4 network the core network structure supports the effective use of service capabilities. Core Network Planning and Optimisation IN/SCE PSTN/ISDN Other PLMN IP/ATM Backbone External WCDMA IP networks 3G-SGSN Figure 4.9 3G release 5 network architecture (including GSM) (SCE, service creation environment; IMR, IP multimedia register; CPS, connection processing server; GGSN, GPRS gateway service node) The 3GPP release 4 network contains all the possibilities of traffic treatment. If the transaction coming from the access network is packet switched, it may be relayed to the external network either in a packet switched or a circuit switched manner. Also, if the transaction coming from the access network is circuit switched, it may go to the external network either in a circuit switched or a packet switched manner. In the 3GPP release 99 network the nature of the connection (circuit/packet) remains the same through the network. The 3G release 4 network elements also ensure future proof investment as all the new network elements introduced can be upgraded to support future releases. The MGW for a legacy PSTN interconnect may also be used in an all-IP network. This will also provide operators with an early experience for voice transport over the IP. Circuit Switched Data Server (CDS) Mobile circuit switched data requires a suitable interworking function (IWF) to be provided by the core network. In the 3GPP release 4 architecture this functionality is located in the media gateway (MGW), but in the pre-release 4 architecture it is located in the MSC. Some vendors do not provide integrated interworking functions for circuit switched data calls in the MGW but rather in the dedicated network node for nontransparent data calls. The IWF functionality is therefore provided in an external circuit switched data server (CDS). 4.3.4 3GPP Release 5 and 6 Networks The 3GPP release 5 network aims to introduce a UMTS network where the transport network