Question: Upon receiving an SGsAP-RESET-INDICATION message from the VLR, what action does the MME take regarding the "VLR-Reliable" MM context variable, and what is a potential subsequent action for a UE attached for non-EPS service sending a periodic tracking area update request?
Option 1: Sets "VLR-Reliable" to "true" and always performs a network-initiated detach with detach type "IMSI detach" after the periodic update.
Option 2: Sets "VLR-Reliable" to "false" but takes no immediate action for periodic tracking area updates from UEs attached for non-EPS services.
Option 3: Resets all UE connections and initiates a full system restart upon setting "VLR-Reliable" to "false", regardless of the update type received from the UE.
Option 4: Sets "VLR-Reliable" to "false" and, for a periodic tracking area update request from a non-EPS attached UE, may either perform a network-initiated detach with detach type "IMSI detach" or immediately perform a location update for non-EPS services, based on network configuration and operator policy.
Explanation: Upon receiving an SGsAP-RESET-INDICATION, the MME sets the "VLR-Reliable" MM context variable to "false", indicating all SGs associations with that VLR are no longer reliable. For a UE attached for non-EPS services sending a periodic tracking area update request, the MME’s subsequent action depends on network configuration and operator policy, allowing for either a network-initiated detach or an immediate location update for non-EPS services, as outlined in the correct option. This reflects the nuanced handling based on the "VLR-Reliable" status and the type of update received from the UE.