Question: Upon Network Authentication Failure in a 3GPP IP-based service scenario, what action does the UE take regarding communication with the P-CSCF?
Option 1: The UE initiates a new Security Association (SA) setup before sending any messages to the P-CSCF.
Option 2: The UE sends a REGISTER message, which may utilize an existing SA, to inform the P-CSCF of the authentication failure.
Option 3: The UE terminates all existing SAs before attempting to re-authenticate with the network through the P-CSCF.
Option 4: The UE bypasses the P-CSCF and directly contacts the Serving CSCF (S-CSCF) for assistance.
Explanation: In the event of a network authentication failure, the User Equipment (UE) notifies the Proxy Call/Session Control Function (P-CSCF) about this failure via an existing Security Association (SA) if already established, ensuring the P-CSCF is aware and can take appropriate actions.