Section: 4.22.10.2 UE or network requested MA PDU Session Release (non-roaming and roaming with local breakout)
Content: The signalling flow for a MA PDU Session Release 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 4.3.4.2-1 with the following differences and clarifications: - In step 1, if the AMF needs to release the MA PDU Session over a single access, the AMF invokes the Nsmf_PDUSession_UpdateSMContext service operation to request the release of the MA PDU Session over a single access. In this case, the AMF includes in which access the MA PDU Session should be released. NOTE: When the SMF received the release request from the AMF, the SMF decides whether the MA PDU Session is completely released or released over a single access based on its local policy. - In step 1, if the AMF needs to release the MA PDU Session (e.g. locally released when the UE is CM-IDLE), the AMF invokes the Nsmf_PDUSession_ReleaseSMContext service operation to request the release of the MA PDU Session. - In step 2a, if the SMF releases the MA PDU Session over a single access, the SMF sends an N4 Session Modification Request (N4 Session ID) message instead of N4 Session Release message to the UPF(s) of the MA PDU session. - In step 2b, the UPF acknowledges the N4 Session Modification Request by the transmission of an N4 Session Modification Response (N4 Session ID) message to the SMF. - In step 3, the SMF sends the PDU Session Release Command message to release the MA PDU session over a single access (either 3GPP access or non-3GPP access) or both accesses. - In step 3, if the SMF releases the MA PDU Session over a single access, the SMF shall not include "skip indicator" in the Namf_Communication_N1N2MessageTransfer service. - In step 3, if the SMF releases the MA PDU Session over both accesses and user plane resources are established in both accesses, the SMF includes both N1 SM container (PDU Session Release Command) and N2 SM Resource Release request together in the Nsmf_PDUSession_UpdateSMContext or Namf_Communication_N1N2MessageTransfer service so that the UE does not request to activate user plane resources. The SMF releases user plane resources of the other access by including N2 SM Resource Release only in Namf_Communication_N1N2MessageTransfer service. - In step 3, 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 11, the SMF triggers Nsmf_PDUSession_SMContextStatusNotify service only when the MA PDU Session is released in both accesses.