Question: In an IP Multimedia Subsystem (IMS), when and why might a Proxy-CSCF (P-CSCF) subscribe to a Policy Control Function (PCF) for notification of an EPS Fallback event?
Option 1: Always, to monitor network congestion in the 5G System (5GS).
Option 2: During registration, to authenticate User Equipment (UE) location.
Option 3: Based on local configuration, during originating or terminating sessions, to potentially include fallback information in outgoing SIP messages.
Option 4: Never, as EPS Fallback is handled solely by the PCF without notification.
Explanation: The correct answer reflects a scenario where a P-CSCF, based on local configuration and during session handling (originating or terminating), may subscribe for EPS Fallback event notifications from the PCF. This is to possibly inform other IMS nodes through outgoing SIP messages, ensuring seamless communication and adaptability within the network.