Question: Which of the following CSCFs is primarily responsible for forcing the release of resources used for an IM Session, specifically for a roaming User Equipment (UE: User Equipment)?
Option 1: S-CSCF serving the originating UE
Option 2: P-CSCF serving the originating or terminating UE
Option 3: I-CSCF handling mid-session changes
Option 4: Application Server (AS) managing service logic
Explanation: In the context of IMS sessions, especially for roaming UEs, the P-CSCF (Proxy-Call Session Control Function) plays a crucial role in resource management. It ensures that resources allocated for the session are properly released when no longer needed. This is critical for efficient network operation and billing (e.g., generating CDR records in roaming cases). While S-CSCFs handle service logic invocation and also generate CDRs at session termination, the P-CSCF's role in forcing resource release, particularly highlighted for roaming scenarios, makes it the correct choice. I-CSCFs may assist with mid-session changes but are not primarily responsible for resource release, and Application Servers manage service logic rather than network resources.