Section: 5.34.7.1 UE's Mobility Event Management
Content: When an I-SMF is involved in a PDU Session, the SMF and I-SMF independently subscribe to "UE mobility event notification" service provided by AMF. The AMF treats the SMF's and I-SMF's subscription separately and notifies the event directly to the SMF or I-SMF. If the SMF does not know the serving AMF address, the SMF gets the serving AMF address from the UDM as described in clause 5.2.3.2.4, TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and subscribes directly with the serving AMF. In the case of AMF change (e.g. Inter NG-RAN node N2 based handover), the target AMF receives mobility event subscription information from the source AMF and updates the mobility event subscription information with the SMF and I-SMF independently (i.e. target AMF allocates the Subscription Correlation ID for each event and notifies the respective SMFs and I-SMF as described in clause 5.3.4.4). In the case of I-SMF change or I-SMF insertion (e.g. at Inter NG-RAN node N2 based handover), the subscription of mobility event (from AMF) is not transferred from the old I-SMF or SMF to the new I-SMF, the new I-SMF triggers a new subscription event if the new I-SMF wants to receive the corresponding mobility event. In the case of I-SMF removal, the subscription of mobility event at the AMF is not transferred from the old I-SMF to the SMF, the SMF triggers a new subscription event if the SMF wants to receive the corresponding mobility event. The subscription from the old SMF entity (old I-SMF, SMF) is removed via an explicitly request from this old SMF entity.