This clause captures enhancements to procedures in TS 23.402
to support interworking with 5GS. The architecture for interworking is shown in clause 4.3.4 of TS 23.501
. with the ePDG connected to SMF+PGW-C and UPF+PGW-U using GTP based S2b.
Clause 220.127.116.11 of TS 23.402
applies with the following modification:
Tracking/Location Area Identity FQDN: When the 5GC NAS capable UE uses the Tracking Area of the NG-RAN when the UE is registered with the 5GC when constructing the Tracking Area Identity FQDN.
The procedure in clause 7.2.4 of TS 23.402
applies with the following modifications:
In Step A.1 IKEv2 tunnel establishment procedure, the 5GC NAS capable UE shall indicate its support of 5GC NAS in IKEv2. The UE allocates a PDU Session ID and also includes this in IKEv2 to the ePDG.
In Step A.1, UE's mobility restriction parameters related to 5GS or indication of support for interworking with 5GS for this APN or both as defined for MME in clause 4.11.0a.3 apply to the ePDG and are obtained by the ePDG as part of the reply from the HSS via the 3GPP AAA Server. These parameters and the 5G NAS support indicator from the UE, may be used by the ePDG to determine if a combined SMF+PGW-C or a standalone PGW should be selected.
In Step B.1, if the UE supports 5G NAS and the PDN connection is not restricted to interworking with 5GS by user subscription, the ePDG shall send the 5GS Interworking Indication and the PDU Session ID to the SMF+PGW-C.
In Step B.1, if the SMF+PGW-C supports more than one S-NSSAI and the APN is valid for more than one S-NSSAI, the SMF+PGW-C selects S-NSSAI as specified in clause 4.11.0a.5.
In Step D.1 (Create Session Response), the SMF+PGW-C assigns a S-NSSAI to be associated with the PDN connection as specified in clause 18.104.22.168 of TS 23.501. The SMF+PGW-C sends the S-NSSAI to the ePDG together with a PLMN ID that the S-NSSAI relates to.
In Steps B.1 and D.1, if the UE does not support 5GC NAS but has 5GS subscription, and a SMF+PGW-C is selected and interaction with UDM, PCF and UPF is required, the SMF+PGW-C assigns PDU Session ID as specified in clause 4.11.0a.5. The SMF+PGW-C shall not provide any 5GS related parameters to the UE.
In the IKEv2 Authentication Response message, the ePDG sends S-NSSAI and the PLMN ID that the S-NSSAI relates to, to the UE. The UE associates the received S-NSSAI and the PLMN ID that the S-NSSAI relates to, with the PDN Connection.
After step D.1, the SMF+PGW-C provides the PCF ID selected for the PDN connection in the UDM using the Nudm_UECM_Registration service operation.
The procedure in clause 7.2.5 of TS 23.402
applies with the following modification:
Step 3 (Create Session Request): ePDG determines if interworking with 5GC is supported based on UE's 5G NAS capability and local configuration. In SMF+PGW-C, only one S-NSSAI is configured for the emergency APN. An emergency SMF+PGW-C identity should be configured as part of the Emergency Configuration Data specified in clause 13.5 of TS 23.402.
Step 6 (Create Session Response), compared to step D.1 of clause 22.214.171.124.3, SMF+PGW-C does not include S-NSSAI in PCO for emergency PDN connection.
When interworking with 5GS is supported and a SMF+PGW-C is selected by the ePDG, policy interactions between PDN GW and PCRF specified in TS 23.402
are replaced by equivalent interactions between SMF+PGW-C and PCF as captured in clause 4.11.0a.2
If SMF+PGW-C is selected and interaction with PCF is required for a UE that does not support 5GC NAS, the SMF+PGW-C determines the PDU Session ID and S-NSSAI in the same way as for PDN connection via MME as specified in clause 4.11.0a.5
The procedure in clause 7.6.3 of TS 23.402
references the Initial Attach procedure with GTP on S2b. Impacts to the initial attach procedure with GTP on S2b are captured in clause 126.96.36.199.3
above. If the additional PDN connection is for emergency service, impact as captured in clause 188.8.131.52.3a
This clause applies to scnearios when ePDG is connected to SMF+PGW-C and S6b in not used. It is applicable for procedures specified in TS 23.402
including mobility between EPC/ePDG and EPC/EUTRAN and also for mobility between EPC/ePDG and 5GS.
When S6b, as specified in TS 23.402
, is not deployed between SMF+PGW-C and AAA and the UE creates and deletes a PDN connection via ePDG connected to SMF+PGW-C, the registration and de-registration of PDN GW is performed on the N10 interface instead of the S6b interface.
If SMF+PGW-C is selected for a UE that does not support 5GC NAS, the SMF+PGW-C determines the PDU Session ID and S-NSSAI in the same way as for PDN connection via EPC/EUTRAN as specified in clause 4.11.0a.5
For roaming scenario with local-breakout (TS 23.501
, Figure 184.108.40.206-1
), the use of N10 interface instead of S6b interface may be based on support of this feature from HSS+UDM to SMF+PGW-C on N10 interface.
The specific impacts to procedures in clauses 7
and 8 of TS 23.402
are as follows:
7.2.4 Initial Attach with GTP on S2b
7.2.5 Initial Attach for emergency session (GTP on S2b)
Instead of Step C.1 in Figure 7.2.4-1 of TS 23.402, step 16c (Nudm_UECM_Registration with an optional indication that access is from ePDG) from Figure 220.127.116.11.1-1 are performed between the SMF+PGW-C and HSS+UDM. Based on this indication, the HSS+UDM does not send notification of PGW-C assignment on SWx to AAA.
7.4.3 UE/ePDG-initiated Detach Procedure and UE-Requested PDN Disconnection with GTP on S2b
Instead of step 5 in Figure 7.2.5-1 of TS 23.402, step 16c (Nudm_UECM_Registration with an optional indication that access is from ePDG) from Figure 18.104.22.168.1-1 are performed between the SMF+PGW-C and HSS+UDM. Based on this indication, the HSS+UDM does not send notification of PGW-C assignment on SWx to AAA.
The indication of access from ePDG is forwarded on the interface between UDM and HSS.
Non-Roaming, Home Routed Roaming and Local Breakout Case
7.4.4 HSS/AAA-initiated Detach Procedure with GTP on S2b
22.214.171.124 Non-Roaming, Home Routed Roaming and Local Breakout Case
7.9.2 PDN GW initiated Resource Allocation Deactivation with GTP on S2b
126.96.36.199 General Procedure for GTP based S5/S8 for E-UTRAN Access
188.8.131.52 3GPP Access to Untrusted Non-3GPP IP Access Handover with GTP on S2b
In Step B.2 of clause 184.108.40.206 of TS 23.402, if the registration of the SMF+PGW-C in the HSS+UDM is not already done, step 16c (Nudm_UECM_Registration with an optional indication that access is from ePDG) from Figure 220.127.116.11.1-1 is performed between the SMF+PGW-C and HSS+UDM.
The impacts to procedure in clause 18.104.22.168
(Handover from EPC/ePDG to 5GS) are as follows:
For step 0, the impacts to clause 7.2.4 of TS 23.402 are captured above.
In step 2, if the Request Type indicates "Existing Emergency PDU Session", the AMF shall use the Emergency Information containing SMF+PGW-C FQDN for the S2b interface and the S NSSAI locally configured in Emergency Configuration Data.
In step 3, the impacts to clause 7.9.2 of TS 23.402 are captured above. Nudm_UECM_Deregistration is not performed by SMF+PGW-C, as resources in the SMF+PGW-C are not released.
The impacts to procedures in clause 22.214.171.124
(Handover from 5GS to EPC/ePDG) are as follows:
For step 2, impacts to clause 126.96.36.199 (3GPP Access to Untrusted Non-3GPP IP Access Handover with GTP on S2b) of TS 23.402 are captured above and Step 16c of Figure 188.8.131.52.1-1 is not performed as SMF+PGW-C already registered in the HSS+UDM when the UE is in 5GS.