Question: Under what condition, except for NAS level mobility management congestion control, does the MME send an SGsAP-EPS-DETACH-INDICATION to a VLR with the indication 'EPS services not allowed'?
Option 1: When a UE initiates a detach request from EPS services and the SGs association state is not SGs-NULL.
Option 2: When the MME rejects a combined or periodic Tracking Area Update (TAU) procedure for a UE with an existing SGs association.
Option 3: When the VLR requests an EPS detach for a specific IMSI due to resource constraints.
Option 4: When the SGSN sends a Detach Notification with a Detach type indicating 'CS Detach' to the MME.
Explanation: If the combined or periodic Tracking Area Update (TAU) procedure is rejected by the MME (excluding NAS level mobility management congestion control cases), and the UE has an SGs association state different from SGs-NULL, the MME sends an SGsAP-EPS-DETACH-INDICATION to the VLR indicating 'EPS services not allowed', aligning with this scenario.