UE reachability status leverages the 3GPP network monitoring functionality exposed via T8/N33 reference point detailed in TS 23.502 and TS 29.522. How the MSGin5G Server determines whether and how (e.g., via request/response or subscription) to monitor the UE reachability using the 3GPP Network capabilities is implementation dependent.
The MSGin5G Server sends a one-time Monitoring Request to the 3GPP Network using SCEF/NEF capabilities.
The one-time Monitoring Request includes monitoring type set to UE_REACHABILITY, Maximum Number of Reports of 1 and does not include the Monitoring Duration IE.
If the Monitoring Request is successfully processed, a monitoring response providing the UE(s) reachability status is sent to the MSGin5G Server. The response may include idle mode information e.g., active time granted to the UE, eDRX cycle length, periodic RAU/TAU timer, etc., depending on the parameters indicated in the request.
The MSGin5G Server sends a Monitoring Event Subscribe request to the 3GPP Network using existing SCEF/NEF capabilities.
The Monitoring Event Subscribe is a Monitoring Request with monitoring type set to UE_REACHABILITY , and either the Maximum Number of Reports greater than 1 or the Monitoring Duration IE are included.
Based on the reachability status change of a monitored UE(s), the 3GPP Network sends a Monitoring Notification message for UE reachability to the MSGin5G Server as specified in TS 29.122.
The notification may include idle mode information e.g., active time granted to the UE, eDRX cycle length, periodic RAU/TAU timer, etc., depending on the subscription.
The MSGin5G Server uses the information provided in the UE reachability monitoring event report to update its information on the UE's availability, e.g., MSGin5G Client Availability information. The MSGin5G Server may provide additional services based on reachability information, e.g., forward a stored message, etc.