Question: In the 3GPP SAE security architecture, what happens to an RRC message with a failed integrity check after integrity protection has been activated?
Option 1: The message is buffered for potential retransmission.
Option 2: The concerned message shall be discarded, potentially triggering a recovery procedure on the UE side.
Option 3: The eNB and UE enter into an error resolution handshake to rectify the integrity key mismatch.
Option 4: The system automatically switches to a different integrity protection algorithm.
Explanation: According to the specified security architecture, if a failed RRC integrity check is detected after starting integrity protection, the message in question is discarded. This discard can occur on either the eNB or UE side. Upon detecting such a failure, the UE triggers a recovery procedure, highlighting the importance of managing potential deadlocks from context mismatches.