Section: 4.2.5.2 UE Reachability Notification Request procedure
Content: The UE Reachability Notification Request procedure is illustrated in figure 4.2.5.2-1. Figure 4.2.5.2-1: UE Reachability Notification Request Procedure 1a. [Conditional] When a service-related entity requests the UDM to provide an indication regarding UE reachability, the UDM checks whether that service-related entity is authorized to perform this request on this subscriber. The service-related entity may subscribe in UDM to receive notifications about UE Reachability or UE Reachability for SMS delivery events as defined in clause 4.15.3. NOTE 1: This request for UE Reachability Notification is received in UDM using different interfaces/services depending on the service-related entity. For example, an SBI capable service-related entity can use the Nudm_EventExposure_Subscribe service while an SMS-GMSC using non-SBI interfaces triggers this procedure as described in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7]. The UDM may retrieve from the UDR the list of NF IDs for Network Functions authorized by the HPLMN to request notifications on this UE's reachability. If the entity is not authorized, the UDM may reject the request (e.g. if the requesting entity is recognized as being a valid entity, but not authorized for that subscriber) or discard it silently (e.g. if the requesting entity is not recognized). Appropriate O&M reports are generated. 1b. [Conditional] The UDM stores the identity of the service-related entity. In the case that the service-related entity is an SMS-GMSC using non-SBI interfaces, the UDM stores the SC address within the MWD list. Otherwise, if the service-related entity is an SBI capable service-related entity, the UDM stores the address of the SBI capable service-related entity in the form of a subscription to the Nudm_EventExposure service. If the UE Reachability Notification Request is for SMS over NAS and no SMSF is registered for the target UE, steps 2 to 4 are skipped. Otherwise the UDM sets the URRP-AMF flag parameter and continues with step 2. 1c. [Conditional] An NF (e.g. SMF) may subscribe event of UE reachability status change by using the Namf_EventExposure_Subscribe service operation. Steps 2 to 4 are skipped. The AMF invokes the Namf_EventExposure_Notify service operation to report the current reachability state of a UE to the NF if requested by the consumer NF. 2. [Conditional] If the value of URRP-AMF flag parameter changes from "not set" to "set" and an AMF is registered in the UDM for the target UE, the UDM initiates Namf_EventExposure_Subscribe service operation for UE reachability for UE reachable for DL traffic (SUPI, UE Reachability) towards the AMF. The UDM may indicate if direct notification to NF shall be used by the AMF. When direct notification to NF is indicated to the AMF, the URRP-AMF is not set in the UDM in step 1a for NF initiated requests. If the service-related entity requested UDM to receive notifications about UE Reachability for SMS delivery, the UDM shall not indicate direct notification to NF. NOTE 2: The UDM can trigger UE Reachability Notification Request procedure with two different AMFs for a UE which is connected to 5G Core Network over 3GPP access and non-3GPP access simultaneously. Also, for interworking with EPC, the UDM/HSS can trigger UE Reachability Notification Request procedure with MME as described in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13]. 3. The AMF checks that the requesting entity is authorized to perform this request on this subscriber. If the AMF has an MM Context for that user, the AMF stores the NF ID in the URRP-AMF information, associated with URRP-AMF information flag to indicate the need to report to the UDM or directly to the NF with a UE Activity Notification (see clause 4.2.5.3). 4. [Conditional] For UE reachability for UE reachable for DL traffic, if the UE state in AMF is in CM-CONNECTED state and the Access Type is 3GPP access, the AMF initiates N2 Notification procedure (see clause 4.8.3) with reporting type set to Single RRC_CONNECTED state notification.