Section: 4.22.2.2.1 Home-routed Roaming - UE registered to the same PLMN
Content: When the UE is registered to the same VPLMN over 3GPP access and non-3GPP access, the MA PDU Session is established as specified in Figure 4.3.2.2.2-1 ("UE-requested PDU Session Establishment for home-routed roaming scenarios") with the differences and clarifications: - The PDU Session Establishment Request message may be sent over the 3GPP access or over the non-3GPP access. - In step 1, the UE provides Request Type as "MA PDU Request" in UL NAS Transport message and its ATSSS Capabilities, as defined in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] in PDU Session Establishment Request message. The UE indicates to AMF whether it supports non-3GPP access path switching. - In step 2, if the AMF supports MA PDU sessions, then the AMF selects a V-SMF and an H-SMF, which supports MA PDU sessions. The V-SMF serves the UE over both accesses. If the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF selects a V-SMF and H-SMF supporting non-3GPP access path switching, if such a V-SMF and H-SMF are available. - In step 3, the AMF informs the SMF that the request is for a MA PDU Session by including an "MA PDU Request" indication and in addition, the AMF indicates to V-SMF that the UE is registered over both accesses. If the AMF supports non-3GPP access path switching while maintaining two N2 connections for non-3GPP access, the selected SMFs supports non-3GPP path switching and UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF indicates whether the UE supports non-3GPP path switching to the V-SMF. - In step 5, two DL N9 tunnel CN info and two UL N3 tunnel CN info are allocated by the V-SMF or by the V-UPF. - In step 6, the V-SMF informs the H-SMF that the request is for a MA PDU Session by including an "MA PDU Request" indication and indicates to H-SMF that the UE is registered over both accesses. The V-SMF indicates to H-SMF the relationship between the DL N9 tunnel CN info and the access type. If the single CN Tunnel is established by the H-SMF, the DL N9 tunnel info binding to the access over which the NAS message is received is to be used. - In step 7, the H-SMF retrieves, via Session Management subscription data, the information whether the MA PDU session is allowed or not. - In step 9, if dynamic PCC is to be used for the MA PDU Session, the H-SMF sends an "MA PDU Request" indication to H-PCF in the SM Policy Control Create message and the ATSSS Capabilities of the MA PDU session. The H-SMF provides the currently used list of Access Type(s) and RAT Type(s) for the MA-PDU session to the H-PCF. The H-PCF decides whether the MA PDU session is allowed or not based on operator policy and subscription data. The H-PCF provides the PCC rules containing MA PDU session control information and the H-SMF derives the ATSSS rules for the UE and the N4 rules for the H-UPF. - In step 12, two UL N9 tunnel CN info are allocated by the H-SMF or by the H-UPF. After this step, the two N9 tunnels between the H-UPF and V-UPF are established. - In step 13, the H-SMF sends "MA PDU session Accepted" indication to V-SMF in the Nsmf_PDUSession_Create Response message. The H-SMF indicates to V-SMF the relationship between the UL N9 tunnel CN info and the access type. - In step 14, the V-SMF sends the "MA PDU session Accepted" indication in the Namf_Communication_N1N2MessageTransfer message to the AMF and indicates the AMF to send the N2 SM Information included in this message over the access that the UE sent the PDU Session Establishment Request. The AMF marks this PDU session as MA PDU session based on the received "MA PDU session Accepted" indication. The V-SMF indicates support of non-3GPP path switching in the PDU Session Establishment Accept message. If the V-SMF received two UL N9 tunnel CN info from the H-SMF, the V-SMF also initiates the establishment of user-plane resources over the other access. The V-SMF sends an N1N2 Message Transfer to AMF including N2 SM Information and the other access type to indicate to AMF that the N2 SM Information should be sent over the other access. The N1N2 Message Transfer does not include an N1 SM Container for the UE which was sent to UE over the access that the UE sent the PDU Session Establishment Request. - In step 16, the UE receives a PDU Session Establishment Accept message, which indicates to UE that the requested MA PDU session was successfully established. This message includes the ATSSS rules for the MA PDU session, which were derived by H-SMF and may include Measurement Assistance Information. - After step 20, if the V-SMF was informed in step 3 that the UE is registered over both accesses, then the V-SMF initiates the establishment of user-plane resources over the other access too. The V-SMF sends an N1N2 Message Transfer to the AMF including N2 SM Information and indicates to the AMF over which access the N2 SM Information should be sent. The N1N2 Message Transfer does not include an N1 SM Container for the UE because this was sent to the UE in step 14. After this step, two N9 tunnels between the H-UPF and the V-UPF as well as two N3 tunnels between the V-UPF and RAN/AN are established, or, if the H-UPF is connected to two different V-UPFs, the H-UPF has one N9 tunnel with each V-UPF.