Question: What action does the P-CSCF take when it cannot accept the proposal set sent by the UE in the Security-Set-up command?
Option 1: The P-CSCF requests an alternative security proposal from the UE.
Option 2: The P-CSCF responds with an error response indicating failure to the UE.
Option 3: The P-CSCF proceeds with a default security configuration for the session.
Option 4: The P-CSCF terminates the session without notifying the UE.
Explanation: When the P-CSCF cannot accept the proposed security settings from the UE during the initial Security-Set-up, it communicates this failure to the UE via an error response. This maintains network security integrity, prompting the UE to renegotiate or understand the rejection reason, preventing unauthorized access attempts due to misconfigured security.