Question: Upon receiving an IDENTITY REQUEST message with Identity type set to 'SUCI' from the network, how does a UE behave if timer T3519 is already running?
Option 1: The UE generates a fresh SUCI, sends it in an IDENTITY RESPONSE message, updates the stored SUCI value, and resets timer T3519.
Option 2: The UE sends an IDENTITY RESPONSE message with the newly calculated SUCI and stops timer T3519.
Option 3: The UE sends an IDENTITY RESPONSE message with the stored SUCI without modifying the timer's state.
Option 4: The UE ignores the request until timer T3519 expires.
Explanation: According to the specified behavior, if timer T3519 is running when the UE receives an IDENTITY REQUEST message with Identity type set to 'SUCI', the UE responds by sending an IDENTITY RESPONSE message containing the stored SUCI. This action does not involve generating a new SUCI or stopping the timer at this point, aligning with efficient reuse of previously calculated and stored credentials until the registration process is fully acknowledged.