Question: In the context of periodic local authentication in a 3GPP SAE network, what triggers the eNB to send a Counter Check message to the UE?
Option 1: The expiration of a predetermined time interval since the last successful authentication.
Option 2: The reaching of a critical checking value in the PDCP COUNT associated with any radio bearer, as defined by the visited network.
Option 3: A change in the UE's location, indicating a handover to a new cell.
Option 4: Receipt of a Counter Check Response message from the UE without PDCP COUNT values.
Explanation: The correct answer is Option 2 because, according to the procedure for periodic local authentication, the eNB monitors the PDCP COUNT values for each radio bearer and triggers the Counter Check message when any of these values reaches a critical checking value predefined by the visited network. This ensures data integrity and detects potential discrepancies or security breaches in real-time.