Question: What action may an HLR take if a VLR indicates it does not support a service (e.g., Closed User Group) considered essential by the HLR operator?
Option 1: Ignore the unsupported service and proceed with the subscriber data transfer.
Option 2: Send an error response to the VLR and terminate the procedure.
Option 3: Attempt to find an alternative network path that supports the service.
Option 4: Set the Roaming Restriction Due To Unsupported Feature flag to roaming restricted and send this in a subsequent request.
Explanation: If the VLR does not support a service deemed essential by the HLR operator, the HLR sets the Roaming Restriction Due To Unsupported Feature flag to roaming restricted. This ensures the subscriber's access reflects the visited network's limitations, maintaining service integrity and informing the subscriber of potential restrictions.