Question: In an IP Multimedia Subsystem (IMS), which entity is permitted to invoke the Conference (CONF) service for a Collaborative Session, and what happens to existing Access Legs when this occurs?
Option 1: Any User Equipment (UE) in the Collaborative Session can invoke the CONF service, and existing Access Legs are always terminated.
Option 2: Only the Controller UE can invoke the CONF service, and when it does, existing Access Legs between the Service Centralization and Continuity Application Server (SCC AS) and Controllee UEs can be reused (updated to bind to the new Collaborative Session).
Option 3: The SCC AS itself invokes the CONF service for all Collaborative Sessions, without requiring a request from any UE, and new Access Legs are always established.
Option 4: Invoking the CONF service is not specified for Collaborative Sessions in IMS, leading to session termination upon such a request.
Explanation: This correct answer reflects the specific protocol behavior defined for IMS Service Continuity. The Controller UE's exclusive role in invoking the CONF service ensures centralized management of the Collaborative Session. Allowing existing Access Legs to be reused (updated) minimizes resource overhead and maintains session continuity, highlighting efficient telecom network operation principles.