Content for TS 23.632 Word version: 18.5.0
5.4.5 UE Reachability p. 27
Figure 5.4.5-1 shows the scenario where the HSS receives a Subscription to notification request for UE-reachability from the IMS-AS for a subscriber who has a 5GC subscription.
Step 1.
Figure 5.4.5-2 shows the scenario where the UDM detects UE reachability for SMS over IP and notifies the HSS that has previously subscribed.
The HSS receives a Subscribe request for UE reachability for IP from the IMS-AS.
Step 2.
The HSS reads subscription data from the EPS-UDR.
Step 3.
The HSS sets the UE Reachability flags for EPC and if the UE is registered in EPC contacts the registered MME and SGSN to get notified when the UE becomes reachable.
Step 4.
If the HSS detects in step 2 that the user has a 5GC subscription, the HSS uses the Nudm_EventExposure_Subscribe service operation (one time immediate report requested) to get notified when the UDM detects UE reachability for SMS over IP. Otherwise, continue with step 10.
Step 5.
The UDM sets the URRP-AMF flag in the 5GS-UDR and reads data from the 5GS-UDR to get the AMF for 3GPP Access Registration Information and the AMF for non-3GPP Access Registration Information if any.
Step 6-7.
[Conditional] If an AMF is registered in UDM for the target UE and the UDM has not already subscribed in AMF due to a previous subscription from a different NF, the UDM subscribes to UE reachability notifications at the registered AMFs by means of the Namf_EventExposure_Subscribe service operation (see TS 23.502).
Step 8.
The UDM updates the 5GS-UDR with the EE-Subscription for the HSS.
Step 9.
The UDM acknowledges the EE Subscription to the HSS.
Step 10.
The HSS acknowledges the Sh subscription to the IMS-AS.
Step 11.
The HSS updates the EPS-UDR with the Sh subscription for the IMS-AS.
Step 1.
The UDM receives a Notification or Registration from the AMF.
Step 2.
The UDM reads subscription data from the 5GS-UDR.
Step 3.
The UDM acknowledges step 1 towards the AMF. If an old AMF is registered in the UDM, the UDM sends a Nudm_UECM_DeregistrationNotification service operation to the old AMF.
Step 4.
The UDM notifies the HSS (and any other NF that has subscribed) about the reachability of the UE.
Step 5.
The HSS reads data from the EPS-UDR to see whether an IMS-AS has subscribed do reachability notification.
Step 6.
The HSS acknowledges step 4.
Step 7.
The UDM updates the 5GS-UDR to delete the EE-Subscription(s).
Step 8.
The HSS notifies the IMS-AS about UE reachability for IP.
Step 9.
The IMS-AS acknowledges step 8.
Step 10.
The HSS updates the EPS-UDR to delete the IMS-AS's subscription.
