Section: 5.6.7.2 Enhancement of UP path management based on the coordination with AFs
Content: In order to avoid or minimize service interruption during PSA relocation for a PDU session of SSC mode 3, or a PDU session with UL CL or branch point, according to the indication of "AF acknowledgment to be expected" on AF subscription to corresponding SMF events (DNAI change) (that may be provided in PCC rules received from the PCF as defined in clause 5.6.7.1 except in HR-SBO case or that may be provided directly by V-NEF to V-SMF as defined in TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [130] clause 6.7.2 in case of HR-SBO) or according to local configuration (e.g. DN-related policies) the SMF may wait for a response from the AF after sending a notification (an early notification or a late notification) to the AF. In the case of late notification, based on the indication of "AF acknowledgment to be expected" on AF subscription, the SMF may send the notification before activating the UP path towards a new DNAI (possibly through a new PSA). NOTE 1: Before the UP path toward the new DNAI is activated, application traffic data (if any exists) is still routed toward the old DNAI. The notification sent from the SMF to the AF indicates UP path management events (DNAI change) as described in clause 5.6.7.1. The AF can confirm the DNAI change indicated in the notification with the SMF by sending a positive response to the notification to the SMF or reject the DNAI change by sending a negative response. NOTE 2: The AF can determine whether application relocation is needed according to the notification of DNAI change. If not, the AF can send a positive response to the SMF immediately; otherwise, the AF sends the positive response after application relocation is completed or a negative response if the AF determines that the application relocation cannot be completed on time (e.g. due to temporary congestion). The AF decision and behaviours on application relocation are not defined. However, the new DNAI may be associated with a new AF. In such cases, the SMF and the old AF cancel earlier subscribed UP path management event notifications, and the new AF subscribes to receive UP path management event notifications from the SMF. The AF can include N6 traffic routing information related to the target DNAI in a positive response sent to the SMF. The SMF configures the N6 traffic routing information from the AF response to the PSA on the UP path. The AF can include the EAS relocation Indication to indicate the application(s) to be relocated. In the case of early notification, based on the indication of "AF acknowledgment to be expected" on AF subscription, the SMF does not configure the UP path towards the new DNAI until it receives a positive AF response as specified in clause 4.3.6.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. In the case of late notification, based on the indication of "AF acknowledgment to be expected" on AF subscription, the SMF does not activate the UP path towards the new DNAI until it receives a positive AF response as specified in clause 4.3.5 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. NOTE 3: After the UP path toward the new DNAI is activated, data is routed toward the new DNAI. If the SMF receives a negative response at any time, the SMF keeps using the original DNAI and may cancel related PSA relocation or addition. The SMF may perform DNAI reselection afterwards if needed. The SMF can assume according to local policy a negative response if a response is expected and but not received from the AF within a certain time window. When Early/Late Notification happens, the SMF notifies AF about the target DNAI and may indicate capability of supporting EAS IP replacement in 5GC.When EAS relocation is performed, the AF sends an/a early/late notification response to the SMF after the EAS relocation is completed, which may include the Information for EAS IP Replacement in 5GC. The SMF may instruct the local PSA with the EAS IP address replacement using "Outer Header Creation" as defined in clause 5.8.5.6 and "Outer Header Removal" as defined in clause 5.8.5.3. If local PSA relocation is required, the SMF may request the target local PSA to buffer uplink traffic as described in clause 6.3.5 of TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [130]. AF relocation may be triggered by SMF e.g. in relationship with DNAI change due to UE mobility. In the case of AF relocation involving different DNAI(s), it is possible that the source EHE is unaware of other/target EHE specific deployment details. In such cases, when SMF selects a target DNAI (e.g. based on current UE location), the SMF may determine based on the EDI that the target DNAI is not supported by the source AF. The SMF determines the target AF ID based on the target DNAI and the EDI. Accordingly, as part of Early/Late Notification, the SMF provides the target AF ID to the source AF as described in clause 4.3.6.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3].