 function always located at the entrance to the home network, we can compare this (I-CSCF) to the GMSC in a GSM network. The I-CSCF interrogates the HSS to get information to en- able calls going to the serving CSCF. The interrogating CSCF provides the Incoming Call Gateway (ICGW) and AH functionality. The proxy CSCF, which we may compare to the visited MSC in a GSM network, man- ages address translation/mapping and handles call control for certain types of calls like emergency calls, legally intercepted calls, etc. Towards IP Based Networks MT communications can use both serving CSCF and interrogating CSCF functionality, while MO communications do not require the interrogating CSCF functionality. Both serving CSCF and interrogating CSCF components may come in a single CSCF when needed. We can summarize the CSCF functions from Ref. [7] as follows: ICGW (Incoming Call Gateway) acts as a first entry point and performs routing of incoming calls; incoming call service triggering (e.g. call screening/call forwarding unconditional) may need to reside for optimisation purposes; query address handling (implies administrative dependency with other entities); communicates with HSS. CCF (Call Control Function) call set-up/termination and state/event management; interact with the Multimedia Resource Functions (MRF) in order to support multi- party and other services; reports call events for billing, auditing, intercept or other purpose; receives and process application level registration; query address handling (implies administrative dependency); can provide service trigger mechanisms (service capabilities features) towards ap- plication and services network (VHE/OSA); can invoke location based services relevant to the serving network; can check whether the requested outgoing communication is allowed given the cur- rent subscription. SPD (Serving Profile Database) interacts with HSS in the home domain to receive profile information for the ROO all-IP network user and may store them depending on the SLA with the home do- mai