Section: 6.1.5 Coordination for interworking with ePDG connected to EPC
Content: When the UE establishes a new PDN connection via an ePDG connected to EPC, to enable the transfer of the PDN connection to N1 mode in case of inter-system change, the UE allocates a PDU session identity and indicates its value in the PDU session ID field in the N1_MODE_CAPABILITY Notify payload of the IKE_AUTH request message (see 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16]). The network provides the UE with an S-NSSAI in the N1_MODE_INFORMATION Notify payload of the IKE_AUTH response message (see 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16]). Upon inter-system change to N1 mode , for PDN connection(s) established via an ePDG connected to EPC, if present, the UE may: a) keep some or all of these PDN connections still via ePDG connected to EPC, if supported; b) release some or all of these PDN connections explicitly by initiating the UE initiated tunnel disconnection procedure(s) as specified in 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16]; or c) attempt to transfer some or all of these PDN connections to N1 mode using the parameters of the PDN connection for which the UE has allocated a PDU session identity by initiating the PDU session establishment procedure(s) with the PDU SESSION ESTABLISHMENT REQUEST message created. In that case, for each and every PDN connection to be transferred: 1) if the PDN connection is for emergency bearer services, the request type shall be set to "existing emergency PDU session". Otherwise the request type shall be set to "existing PDU session"; 2) if the previously allocated home address information for a PDN connection consists of an IPv4 address only for an ePDG connected to EPC according to 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16], the PDU session type shall be set to "IPv4"; 3) if the previously allocated home address information for a PDN connection consists of an IPv6 prefix only for an ePDG connected to EPC according to 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16], the PDU session type shall be set to "IPv6"; 4) if the previously allocated home address information for a PDN connection consists of both an IPv4 address and an IPv6 prefix for an ePDG connected to EPC according to 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16], the PDU session type shall be set to "IPv4v6"; 5) the APN of the PDN connection shall be mapped to the DNN of the PDU session; 6) the PDU session ID shall be set to the PDU session identity in the N1_MODE_CAPABILITY Notify payload of the IKE_AUTH request message establishing IPsec tunnel of the PDN connection; and 7) if the PDN connection is not for emergency bearer services, the S-NSSAI of the PDU session shall be set to the S-NSSAI associated with the PDN connection as specified in 3GPP TS 24.302[ Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3 ]  [16]. The UE shall not request to perform handover of an existing PDN connection to N1 mode if the associated S-NSSAI is not included in the allowed NSSAI for 3GPP access. If an existing PDU session is transferred from 3GPP access to an ePDG connected to EPC connection and that existing PDU session is associated with one or more MBS sessions, the UE shall locally leave the associated multicast MBS sessions and the SMF shall consider the UE as removed from the associated multicast MBS sessions.