Question: What happens to the NAS signalling connection when a UE provides unavailability information in the attach procedure or tracking area updating procedure?
Option 1: The MME maintains the NAS signalling connection until the UE registers for normal service without providing unavailability information.
Option 2: The MME releases the NAS signalling connection after the completion of the attach procedure or the tracking area updating procedure in which the UE provided unavailability information.
Option 3: The MME suspends the NAS signalling connection until the UE provides updated unavailability information.
Option 4: The MME terminates the NAS signalling connection and initiates a new attach procedure.
Explanation: According to the text, when a UE provides unavailability information in the attach procedure or tracking area updating procedure, the MME releases the NAS signalling connection after the completion of the procedure. This is done to conserve resources during the unavailability period.