) those elements are duplicated forfigure layout purpose only, they belong to the same Signalling and Data Transfer logical element in the reference model Interface Figure 9.5 Reference Architecture for Release 00 (R4 and R5) after Ref. [7]. The UMTS Network and Radio Access Technology FUNCTIONAL ELEMENTS The presentation of the ROO functional components in the following corresponds to a direct extract from Ref. [7] in order to keep the vocabulary and the context of the rec- ommendations consistent. However, we also describe its prospective implementation and some key applications as illustrated Figure 9.6. Applications SAT SCS WAP SCS Plane MPS SCS Open Standardized Interface (G)MSC Server SGSN Server Server Control Plane T-SGW GCP (H.248) GCP (H.248) R-SGW Multi-service IP Backbone Connectivity Plane Wireline GERAN ATM,IP UTRAN Cable Multi-Service Corporate Access Networks networks Networks Figure 9.6 The Release 00 integrated architecture. 9.3.1 Call State Control Function (CSCF) Logically, the CSCF can be divided into three sub-components: the serving CSCF (S- CSCF), the proxy CSCF (P-CSCF); and the interrogating CSCF (I-CSCF). We use the first to support mobile originated/terminated communications. It provides the Serving Profile Database (SPD) and Address Handling (AH) functionality. The serving CSCF supports the signalling interactions with the UE through the Gm inter- face. The HSS sends the subscriber data to the serving CSCF for storage. It also gets updated through the latter. The CSCF acts as the central point of the IP multimedia control system; as well as gen- eral call control (setup, supervision, and release). It triggers user controlled supplemen- tary services and call leg handling controlled by user call control supplementary ser- vices, e.g. three party call using Multimedia Resource Function (MRF). In addition, it handles user charging and security. We use the Interrogating CSCF (I-CSCF) for Mobile Terminated (MT) communica- tions and to determine routing for mobile terminated calls. With its