Section: 4.22.8.2 UE or network requested MA PDU Session Modification (non-roaming and roaming with local breakout)
Content: The signalling flow for a MA PDU Session Modification when the UE is not roaming, or when the UE is roaming and the PDU Session Anchor (PSA) is located in the VPLMN, is based on the signalling flow in Figure 4.3.3.2-1 with the following differences and clarifications: - In step 1b, the SMF may decide to update ATSSS rules and/or N4 rules based on updated PCC rules. - In step 1d, if the UPF determines that it cannot send GBR traffic over the current ongoing access e.g. based on the N4 rules and access availability and unavailability report from the UE, the UPF shall send Access Availability report to the SMF. When the SMF receives the Access Availability report, the SMF may decide to move the GBR QoS Flow to the other access as described in clause 5.32.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the SMF decides to move the GBR QoS Flow, the SMF triggers this procedure and afterwards moves the GBR QoS Flow to the target access. - In step 3, if the SMF decides to move the GBR QoS Flow to the other access, the SMF sends N2 SM information to the target AN. The PDU Session Modification Command message is sent to the UE to update ATSSS rule of the UE so that the UE sends uplink GBR traffic over the target access. The SMF releases AN resources of the GBR QoS Flow in the source access. - In step 3, when the SMF establishes user plane resources for a QoS flows, the SMF provides QoS profile to the AN as follows: - for Non-GBR QoS Flow, steps 3 to 8 are performed over each access for which the user plane resources are activated. - for GBR QoS Flow allowed in a single access, steps 3 to 8 are performed in the allowed access. - for GBR QoS Flow allowed in both accesses, steps 3 to 8 are performed in the access according to the decision by the SMF (as described in clause 5.32.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). - In step 3, if the SMF wants to update ATSSS rules, the SMF includes updated ATSSS rules in the N1 SM container (PDU Session Modification Command). When the SMF provides N1 SM container and/or N2 SM information, the SMF includes access type in the Namf_Communication_N1N2MessageTransfer to provide routing information to the AMF. - In step 8, if the SMF decides to moves GBR QoS Flow to the other access, the SMF may send updated N4 rules to the UPF.