Question: When a UE re-registers with an active TLS session, and the P-CSCF receives a REGISTER message with a matching IMPI (IMS Private Identity) associated with the TLS Session ID, what action does the P-CSCF take regarding the TLS integrity protection indicator?
Option 1: The P-CSCF includes a TLS integrity protection indicator with the logical value "authentication pending".
Option 2: The P-CSCF forwards the REGISTER message with a TLS integrity protection indicator indicating the logical value "authentication complete".
Option 3: The P-CSCF does not include any TLS integrity protection indicator and challenges the user with a SIP 401 Auth_Challenge.
Option 4: The P-CSCF terminates the TLS session and requests the UE to establish a new one.
Explanation: When the IMPI in the REGISTER message matches the IMPI associated with the TLS Session ID, the P-CSCF verifies this successfully authenticated session. By forwarding the REGISTER message with a TLS integrity protection indicator set to "authentication complete", the P-CSCF efficiently leverages the existing secure context, streamlining the authentication process for the S-CSCF, which may then apply additional authentication measures based on its local security policy.