Question: In an MME-VLR interface (per 3GPP specs), if an MME sends an SGsAP-IMSI-DETACH-INDICATION for a combined IMSI and EPS detach due to a UE's switch off, and the timer Ts9 expires without receiving an SGsAP-IMSI-DETACH-ACK, what action does the MME take regarding the detachment indication message?
Option 1: The MME sends a single final SGsAP-IMSI-DETACH-INDICATION message before considering the detach confirmed.
Option 2: The MME repeats the SGsAP-IMSI-DETACH-INDICATION message up to a maximum of Ns9 times, then awaits further instructions.
Option 3: The MME immediately sends a confirmation of the detach to the UE, assuming successful detachment.
Option 4: The MME initiates a new timer (Ts10) for additional waiting period before taking further action.
Explanation: According to the specified abnormal case handling for switch-off scenarios, if the MME doesn't receive an SGsAP-IMSI-DETACH-ACK after sending a detach indication for a UE that has switched off, it will repeat the detachment indication message up to Ns9 times. This approach ensures reliability in managing the network's state despite potential communication failures or timeouts (Ts9). Option 2 correctly reflects this retry mechanism before potentially taking further actions not specified in the provided context.