Content for  TS 23.548  Word version:  19.0.0

Due to the UE mobility the SMF triggers L-PSA insertion, change or removal for the PDU Session. The insertion, change or removal of L-PSA triggers EAS rediscovery. The L-PSA insertion, change or removal for the PDU Session may be triggered due to update of a common DNAI.

The AF triggers EAS relocation e.g. due to EAS load balance or maintenance, etc. and informs the SMF the related information indicating the EAS relocation, as described in clause 4.3.6 AF influence on traffic routing procedure in TS 23.502. AF may request to add/remove a UE to/from a set of UEs via AF influence on traffic routing procedure in TS 23.502. The PCF updates PCC rule to SMF (i.e. adding/removal of EAS Correlation indication/indication of traffic correlation and Traffic Correlation ID to/from the PCC rule). With the update of the PCC rule, the SMF detects that the UE is belonging to a set of UE(s) for a common EAS/DNAI, or the UE is not belonging to a set of UEs for common EAS/DNAI any longer and the common EAS/DNAI is not optimized for the UE, it may trigger EAS rediscovery. If UE is belonging to a set of UE(s) for a common EAS/DNAI as instructed by the PCC rule, the SMF interacts with NEF for common EAS/DNAI selection as described in clauses 6.2.3.2.5 and 6.2.3.2.6.

This step may be performed as part of step 1a/1b. The SMF performs the network requested PDU Session Modification procedure from the step 3b-11b as defined in clause 4.3.3.2 of TS 23.502. If the UE has indicated that it supports to refresh EAS information stored locally corresponding to the impact field per the EAS rediscovery indication from network, the SMF may send the impact field with the EAS rediscovery indication. SMF determines the impacted EAS(s) which need be rediscovered as the following:

• If an L-PSA is inserted/relocated/removed, the SMF determines the impact field, which is associated with the L-DN to be inserted, relocated or removed and identified by FQDN(s) or IP address range(s) of the old EAS, based on the association between FQDN(s)/IP address range(s) and DNAI provided by AF or SMF local configuration on the L-DN.
• For AF triggered EAS rediscovery, the AF may indicate the EAS rediscovery for the impacted applications, which are identified by Application Identifier(s), to the SMF via the AF influence on traffic routing procedure.

The SMF sends PDU Session Modification Command (EAS rediscovery indication, [impact field]) to UE. The EAS rediscovery indication indicates to refresh the cached EAS information. The impact field is used to identify which EAS(s) information need to be refreshed. The impact field includes the L-DN information corresponding to the impacted EAS(s), which are identified by FQDN(s) or IP address range(s) of the old EAS(s). If the impact field is not included, it means all EAS(s) information associated with this PDU Session need to be refreshed. The SMF may choose new DNS settings for the PDU Session and if so, it provides them to the UE as new DNS server (see Option C in clause 6.2.3.2.3). Otherwise the UE uses the existing DNS server for EAS rediscovery. For the following connection with the EAS(s) for which the EAS rediscovery needs to be executed per the received EAS rediscovery indication and impact field, the UE has been instructed not to use the old EAS information stored locally. Instead it should trigger EAS discovery procedure to get new EAS information as defined in clause 6.2.3.2. For the Split-UE, it is not possible to provide the NAS level EAS rediscovery indication and the impact field to the TE. Annex C documents mitigations for this scenario. When I-SMF based Local Offloading Management applies:

• For EAS rediscovery triggered by UE mobility, the insertion/change/removal of L-PSA, which is related to the local traffic to EAS, is triggered by I-SMF. The I-SMF sends EAS rediscovery indication and optionally impact field to the SMF by invoking Nsmf_PDUSession_Update Request service operation. The SMF sends PDU Session Modification Command to UE as described above.