unication with the CSCF for service validation and for multiparty/multimedia sessions. 9.3.8 MSC and Gateway MSC Server The MSC server includes mainly the call control and mobility control parts of a GSM/ UMTS MSC. It has responsibility for the control of MO and MT 04.08CC CS domain calls. It terminates the user-network signalling (04.08 + CC + MM) and translates it into the relevant network-network signalling. The MSC server also contains a VLR to hold the mobile subscriber's service data and CAMEL related data, controls the parts of the call state that pertain to connection control for media channels in a MGW [7]. The GMSC server comprises primarily the call control and mobility control parts of a GSM/UMTS GMSC. A MSC server and a MGW make up the full functionality of a MSC, while the Gateway MSC and a GMSC server and a MGW make up the full func- tionality of a GMSC. REFERENCE POINTS 9.4.1 Cx Reference Point (HSS-CSCF) The Cx reference point supports information transfer between CSCF and HSS, where the main procedures requiring information transfer between CSCF and HSS include: procedures related to serving CSCF assignment; procedures related to routing information retrieval from HSS to CSCF; 1 Extensions to H.248 may be required. The UMTS Network and Radio Access Technology procedures related to UE-HSS information tunnelling via CSCF. Details on these procedures can be found in Ref. [7]. 9.4.2 Gf Reference Point (SGSN-EIR) The SGSN server supports the standard Gf interface towards the EIR server. MAP sig- nalling is used over this interface in order to support identity (IMEI) check procedures. For more details refer to TS 23.060. 9.4.3 Gi (GGSN-Multimedia IP Network) The GGSN supports the Gi interface. It is used for transportation of all end user IP data between the UMTS core network and external IP networks. The interface is imple- mented according to TS 23.060, the Internet Protocol according to RFC791 and RFC792 (ICMP). Finally, the IPSec according to the following RFCs: 2401, 2402, 2403, 2404, 2405, 2406,