Question: During a Location Registration request, if an MS identifies itself by a TMSI and the LAI is in the current VLR, but the TMSI was allocated before the VLR restarted, how does the VLR proceed?
Option 1: The VLR handles the request as described for valid TMSIs allocated after the restart.
Option 2: The VLR requests the IMSI from the MS to verify the subscriber's identity.
Option 3: The VLR automatically aborts the location registration procedure without requesting additional information.
Option 4: The VLR initiates a 'Search for Subscriber' procedure using the TMSI.
Explanation: When a TMSI was allocated before the VLR restarted, it is considered invalid due to the restart. To ensure accurate identification and proceed with the location registration, the VLR must request the IMSI from the MS to verify the subscriber's identity against valid IMSI records in the restarted VLR.