ocedure may be as follows: information flow A corresponds to the common initiation of the registration infor- mation flows; information flow B occurs in where the serving CSCF) is selected to be in the home network; information flow C occurs where the serving CSCF is selected to be in the visited network. Note: the prefix 'h' indicates that the functional element is located in the home network, the prefix 'V' indicates that the functional element is located in the visited network. When there is no prefix to the functional element the functional element could be in either the visited network or the home network [7]. 9.6.1.2.1 Registration Information Flow A : Start of Registration Proxy hI-CSCF S-CSCF Register Register Cx-Query Cx-Query-Rsp Figure 9.14 Initiating registration. The UMTS Network and Radio Access Technology A1 Register Ue to Proxy Information control: Ue address, subscriber identity, and home domain name. Initiation of information flow: Ue secures a signalling channel in the 'PS' domain, and decides to initiate the IPMM subsystem registration. Processing upon receipt: when the proxy receives the registration request, it exam- lines the home domain name to identify the entry point to the home network. The proxy will then insert its own name in the contact header, as well as insert the local network capabilities and the local network entry point into the register information flow. Then the information flow (A2) initiates. We utilize a name-address resolu- tion mechanism to determine the destination of information flow (A2), with the home domain name as the input. A2 Register Proxy to h-Interrogating CSCF Information control: proxy name, subscriber identity, home domain name, local network contact name (the name that the registration would be returned to in the case of visited serving CSCF), and local network capabilities. Initiation of information flow: receipt of information flow (A1). Processing upon receipt: when the interrogating CSCF receives the register infor- mation flow (1), it queries the HSS