Question: When a UE's SM7 message (carrying response) is received by the P-CSCF, which Security Association (SA) should be used to protect this message if SM1 was previously protected?
Option 1: Old Inbound SA
Option 2: New Inbound SA
Option 3: Registration SA
Option 4: Either Old or New Outbound SA
Explanation: According to security association management in the P-CSCF, when SM1 is protected and the UE responds with SM7 (carrying the response), this message shall be protected using the **New Inbound SA**. This ensures that once the authentication process progresses, new SAs are utilized for protecting subsequent messages, enhancing security by updating encryption keys or parameters.