Question: Under what condition does the PCEF (Policy and Charging Enforcement Function) initiate an IP-CAN Session Termination Request for an IP-CAN session serving an IMS Emergency session after a PCRF-Initiated modification?
Option 1: Immediately after receiving a PCRF-Initiated IP-CAN Session Modification Request that adds new PCC rules.
Option 2: When the last PCC rule for the IP-CAN session is removed, regardless of the session type.
Option 3: Upon expiration of a configurable inactivity timer, if all PCC rules (except those for default bearer QCI and IMS signalling QCI) are removed for an IMS emergency session.
Option 4: Directly after a PCRF-Initiated IP-CAN Session Modification Request removes all PCC rules with any QCI for an IMS non-emergency session.
Explanation: This is the correct answer because when all PCC rules with a QCI other than the default bearer QCI and the QCI used for IMS signalling are removed for an IP-CAN session serving an IMS emergency session, the PCEF starts a configurable inactivity timer. Only after this timer expires does the PCEF initiate an IP-CAN Session Termination Request for that session, potentially allowing for PSAP Callback sessions.