Question: In the context of Wireless and Wireline Convergence for the 5G System (5GS), what triggers a UE-initiated deregistration procedure for a Fixed Network - Radio Access Gateway (FN-RG) from the perspective of the Wireline-5GAN Access Function (W-AGF)?
Option 1: Receipt of a NAS deregistration request message directly from the User Equipment (UE)
Option 2: Loss of connectivity between the W-AGF and the FN-RG
Option 3: Expiration of a predefined timer set for periodic deregistration checks
Option 4: Change in the Quality of Service (QoS) requirements for an ongoing session
Explanation: The correct answer, Option 2, highlights a specific condition under which the W-AGF initiates a UE-initiated deregistration procedure on behalf of the FN-RG. This is based on the understanding that the W-AGF acts as an intermediary and can trigger this procedure when it detects a loss of connectivity to the FN-RG, ensuring seamless management of converged access in the 5GS. The other options are incorrect because they either describe direct UE interactions, unspecified timer-based actions, or unrelated QoS adjustments.