Section: 4.23.5.4 SMF triggered I-SMF selection or removal
Content: Figure 4.23.5.4-1: SMF triggered I-SMF selection or removal 1. The PCF sends to the SMF PCC rule(s) which may include DNAI(s) for the PDU sessions by invoking Npcf_SMPolicyControl_UpdateNotify service operation. Based on the received DNAI(s), the SMF may subscribe to UE mobility event notification from the AMF (e.g. UE moves into or out of Area of Interest corresponding to the received DNAI(s)). The SMF may determine the target DNAI(s) which are applicable to the current UE location and which can be based on common DNAI (if applicable) as described in TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [74]. Then the SMF may decide a target DNAI finally. NOTE: It is also possible that the SMF determines that there is no any target DNAI can be used based on PCC rule(s), e.g. when the updated PCC rules removes previously provided DNAI(s). 2. The SMF invokes a Nsmf_PDUSession_SMContextStatusNotify service operation (or Nsmf_PDUSession_StatusNotify) in the following cases: - if the SMF (or the associated old I-SMF) cannot serve the target DNAI, or - if an I-SMF is used for the PDU Session and the SMF decides that the DNAI currently served by I-SMF is no longer be used for the PDU Session anymore hence the existing I-SMF is not needed, or - if an I-SMF is used for the PDU Session and the SMF decides that the SMF itself can serve the target DNAI hence the existing I-SMF is not needed. The content of the message includes the target DNAI information. The target DNAI information which indicates that the I-SMF selection or removal is expected and may include a target DNAI. This is to trigger the AMF to (re)select a suitable I-SMF, or remove the existing I-SMF (if the AMF decides that the SMF can serve the Target DNAI, or the AMF receive a target DNAI information without including target DNAI) for the PDU Session. The target DNAI is used for selecting (I-)SMF, which controls UPF connecting to that DNAI. If there is an I-SMF serving the PDU session, the SMF invokes Nsmf_PDUSession_StatusNotify and then the I-SMF invokes Nsmf_PDUSession_SMContextStatusNotify message to send the target DNAI information for existing PDU session to AMF. 3. If the I-SMF selection or removal is expected, the AMF selects a new I-SMF which can serve the target DNAI or remove the existing I-SMF (if the AMF decides that the SMF can serve the Target DNAI, or if the AMF receiveS a target DNAI information without including target DNAI) for the existing PDU Session as described in clause 5.34.3 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 4. The AMF sends a Nsmf_PDUSession_CreateSMContext Request to the new I-SMF as described in step 3 of clause 4.23.4.3, or to the SMF as described in step 10 of clause 4.23.4.3, with the following enhancement: The AMF includes target DNAI received from SMF in the message. When the UE is in CONNECTED state the AMF also include indication of no NG-RAN change. 5. The procedure described in clauses 4.23.4.3 (case: I-SMF insertion or I-SMF change) starting from step 4 takes place with the following difference: In step 4a, the (target) new I-SMF sends the indication of no NG-RAN change to the old I-SMF or SMF as it is received from AMF. In step 4b, when the old I-SMF or SMF receives indication of no NG-RAN change it include the additional Downlink Tunnel Info of NG-RAN in the SM context of the PDU Session. In step 5, the I-SMF selects the I-UPF based on target DNAI. In step 6, the target I-SMF should reuse the downlink Tunnel Info of serving RAN node if received from old I-SMF/SMF as described in clause 4.23.4.3. In step 9, if the new I-SMF receives the Downlink Tunnel Info of NG-RAN, the N2 SM information includes PDU Session Resource Modification message. The procedure described in clause 4.23.4.3 (case: I-SMF removal) starting from step 11 takes place with the following difference: In step 11a, the SMF sends an indication of no NG-RAN change to the old I-SMF as it received from AMF. In step 11b, when the old I-SMF receives indication of no NG-RAN change it include the additional Downlink Tunnel Info of NG-RAN in the SM context of the PDU Session. In step 12, the SMF selects a new I-UPF based on target DNAI. In step 16, if the SMF receives the Downlink Tunnel Info of NG-RAN, the N2 SM information includes PDU Session Resource Modification message. If the UE is in IDLE state the step 17-21 are skipped. Steps 17a and 17b are still performed to release the old I-SMF. 6. [Conditional] In the case that I-SMF insertion or I-SMF change is performed in step 5, the PSA and UL CL/BP controlled by I-SMF is inserted as described from steps 2 to 11 in figure 4.23.9.1-1 with the following difference: In step 2, the I-SMF selects a new PDU Session Anchor (PSA2) based on the target DNAI received in step 4. For the case of I-SMF removal, the PSA and UL CL/BP controlled by SMF is inserted as described from steps 2 to 8 in Figure 4.3.5.4-1 with the following difference: In step 2, the SMF selects a new PDU Session Anchor (PSA2) based on the target DNAI if received in step 4.