Question: When a 3GPP subscriber's online charging account expires, triggering disconnection from WLAN interworking service, what message does the 3GPP AAA Server send to the 3GPP AAA Proxy to initiate the process?
Option 1: Account_Update_Request message with expiration details
Option 2: Session_Termination_Notification message without a specific reason
Option 3: Authentication_Rejection message citing account issues
Option 4: Either Disconnect_Request or Diameter_Abort_Session_Request message carrying a Session-ID
Explanation: According to the immediate purging of a WLAN user process, when a trigger (such as an online charging account expiration) requires disconnection, the 3GPP AAA Server initiates the process by sending either a Disconnect_Request (if using RADIUS) or a Diameter_Abort_Session_Request (if using Diameter) to the 3GPP AAA Proxy. Both messages are designed to carry a Session-ID for identifying the session within the WLAN Access Network (WLAN AN), ensuring targeted disconnection.