Question: In a 3GPP Evolved Packet System (EPS), which of the following statements about integrity protection for signaling messages is correct?
Option 1: All NAS and RRC signaling messages are always integrity-protected, with no exceptions.
Option 2: Most NAS and RRC signaling messages are integrity-protected, except for explicitly listed exceptions.
Option 3: Integrity protection for NAS and RRC signaling messages is only mandatory during authenticated emergency calls.
Option 4: There is no integrity protection for NAS or RRC signaling messages when the UE is in Limited Service Mode.
Explanation: This option correctly reflects the nuanced approach to integrity protection. Most, but not all, NAS and RRC signaling messages are protected, with specific exceptions. This ensures a balance between security and operational flexibility. Option 1 is incorrect due to existing exceptions. Option 3 misrepresents conditions under which integrity protection can be omitted (unauthenticated emergency calls). Option 4 overgeneralizes, as integrity protection omission is specific to unauthenticated emergency scenarios, not all Limited Service Mode operations.