CSCF to h S-CSCF or V I-CSCF Information control Initiation of information flow: receipt of information flow (A5). Processing upon receipt: the behaviour of the h-interrogating CSCF depends on whether the serving CSCF is determined to be in the home network of the visited network. When the serving CSCF corresponds to the home network, then the h- interrogating CSCF has the name of the serving CSCF, and information flow (H1) is initiated. When the serving CSCF corresponds to the visited network, the h- interrogating CSCF has the name of the v-interrogating CSCF, which was provided to the home network in information flow (A2), and information flow (V1) is initi- ated. A name-address resolution mechanism is utilized in order to determine the destination of information flow (H1) or (V1), with the serving CSCF name or V- interrogating CSCF name as the input. See details of information flows A, B and C still under consolidation in [7]. MULTIMEDIA SIGNALLING Although multimedia signalling also remains under consolidation within the technical specification bodies of the 3GPP, we can still describe the initial principles based on [7] and extrapolated for R4 and R5 as follows: A single call control between the UE and CSCF For multimedia type services delivered via the PS domain within R4 and R4 architectures, we aim to use a single call control protocol between the user equipment UE and the CSCF (over the Gm reference point). Protocols over the Gm reference point The single protocol applied between UE and CSCF (over the Gm reference point) within the R4 and R4 architectures Although it may have occurred at an earlier point in the message flows. The UMTS Network and Radio Access Technology will be based on SIP (as defined by RFC 2543, other relevant RFCs, and additional enhancements required to support 3GPP's needs). A single call control on the Mw, Mm, Mg We aim to use single call control pro- tocol on the call control interfaces between MGCF and CSCF, between CSCFs within one operator's network and between CSCFs in differ