Question: During an ongoing IMS registration procedure, if a UE receives a message protected with an incorrect Security Association (SA), how should the UE handle this message?
Option 1: The UE shall process the message but log a security alert.
Option 2: The UE shall discard the message and continue with the registration using the old SAs.
Option 3: The UE shall respond with an error message protected by the new outbound SA.
Option 4: The UE shall pause the registration procedure until a valid message is received.
Explanation: According to the security protocols for IMS registrations, if a UE receives a message protected with an incorrect SA, it must ensure the integrity of the authentication process. Discarding the message prevents potential security breaches and allows the UE to continue the registration securely using the established old SAs until new ones are successfully created.