Section: 4.11.5.2 Registration procedure
Content: The following impacts are applicable to clause 4.2.2.2 (Registration procedure): - Step 1: If the Registration type is set to "Initial Registration", the UE is not registered in EPS and the UE provides the 5G-GUTI mapped from EPS GUTI as the old GUTI, then the UE includes complete EPS Attach Request in the Registration request message. - Step 4: If the Registration type is "Initial Registration" as in step 1 of the Registration Procedure captured in clause 4.2.2.2.2, the target AMF may perform Identification Request towards MME along with complete EPS Attach Request message for MME to verify it as in step 3 as specified in clause 5.3.2.1 of TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13]. NOTE 1: The steps above apply to interworking with N26. - Step 14a: - If the AMF does not have event subscription information from the UDM, the AMF indicates it in Nudm_UECM_Registration. The UDM then provides event subscriptions (possibly retrieved from UDR) if any. - If mobility between GERAN/UTRAN and 5GS is required (as specified in clause 5.17.2.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]), at Initial Registration, the AMF serving 3GPP access shall also register with the Nudm_UECM_Registration even if the AMF has a valid context. - Step 14d: If mobility between GERAN/UTRAN and 5GS is required (as specified in clause 5.17.2.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]), when the UDM stores the associated 3GPP Access Type together with the serving AMF as indicated in step 14a, it will also cause cancellation of any other previously registered serving node (e.g. MME if AMF does not indicate not to cancel or SGSN) via HSS/HLR. NOTE 2: Upon mobility from GERAN/UTRAN to 5GS as specified in clause 5.17.2.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the previously registered SGSN needs to be cancelled from HSS/HLR, otherwise the incoming session can fail. - Step 15: As described in clause 6.3.7.1 , clause TS 23.501[ System architecture for the 5G System (5GS) ]  [2], if the AMF receives PCF Selection Assistance info and PCF ID(s) from the UDM, the AMF checks the PCF Selection Assistance info provided by UDM. If a list of DNN,S-NSSAI combinations are provided in the PCF Selection Info the AMF checks local configuration to determine which DNN,S-NSSAI to use then selects the PCF ID included in the corresponding UE Context in the SMF data. If no PCF ID is received, e.g. EPS interworking is not supported, or no PDN connection and related PCC association exists , the AMF select the PCF by considering other criteria, defined in clause 6.3.7.1 TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. - At the end of registration procedure, the AMF may initiate synchronization of event subscriptions with the UDM if the AMF does not indicate unavailability of event subscription in step 14a. NOTE 3: The details how synchronization can be done is left to stage 3. For PDU Session via 3GPP access the following impacts are applicable to clause 4.2.2.2 (Registration procedure) when the UE has established PDU Session(s): In clause 4.3.2.2.1 Non-roaming and Roaming with Local Breakout: - Step 17: Additional trigger for step 17 Nsmf_PDUSession_UpdateSMContext are: - If status of interworking with EPS for a PDU session changes, e.g. due to change of 5GMM capability (e.g. "S1 mode supported"), the UE subscription data change (e.g. Core Network Type Restriction to EPC), the AMF invokes Nsmf_PDUSession_UpdateSMContext (EPS Interworking Indication with N26 or without N26) to SMF. The SMF determines whether the PDU session supports interworking with EPS need be changed. If it needs to be changed, the SMF invokes Nudm_UECM_Update service operation to add or remove the PGW-C FQDN for S5/S8 interface from the UE context in SMF data stored at the UDM. For interworking with the N26 interface, if status of interworking with EPS for a PDU session is changed at SMF+PGW-C, the SMF+PGW-C invokes EBI allocation or revocation as described in clause 4.11.1.4.1 and clause 4.11.1.4.2 respectively. For PDU Session via non-3GPP access, the AMF determines if EPS interworking is supported and sends the indication to the SMF in the same way as for PDU Session via 3GPP access. The SMF makes the final decision on the EPS interworking in the same way as for PDU Session via 3GPP access with the following modification: If the SMF does not receive the interworking indication, the SMF makes its decision based on subscription.