6.1.5 Coordination for interworking with ePDG connected to EPC

24.5013GPPNon-Access-Stratum (NAS) protocol for 5G System (5GS)Release 17Stage 3TS

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 [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 [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 [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 [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 [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 [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 [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 the target access.