Question: During an IMS (IP Multimedia Subsystem) session, when are subsequent signaling communications integrity protected, according to the security association set-up procedure?
Option 1: Immediately after the initial SIP (Session Initiation Protocol) request is sent
Option 2: Based on keys derived during the user authentication process performed at registration
Option 3: Only after a separate integrity protection protocol is initiated by the User Equipment (UE)
Option 4: Concurrently with the start of media transfer (e.g., voice, video)
Explanation: The correct answer is Option 2 because, as outlined in the security association set-up procedure for IMS, user authentication occurs during the registration phase. This process derives keys that are subsequently used to integrity protect any signaling communications within that session, ensuring the authenticity and integrity of the signals exchanged.