Section: 4.22.2.4.2 PDN Connections and Multi Access PDU Sessions
Content: When the UE wants to request a new PDN Connection in EPC and wants to use this PDN Connection as user-plane resource associated with a MA PDU Session: - The UE requests establishment of a new PDN Connection when the UE is registered via non-3GPP access in EPS using PDN Connection Establishment procedure. The UE provides the following ATSSS information to ePDG via IKE signalling: - An indication that the PDN Connection is requested to be associated with a MA PDU Session - The UE's ATSSS capabilities as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] (i.e. whether the UE is capable of supporting any combination of the ATSSS-LL functionality, the MPTCP functionality and the MPQUIC functionality). - The ePDG may select a PGW-C+SMF as described in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26]. The ePDG forwards the ATSSS information to the selected PGW-C+SMF via APCO in Create Session Request message. NOTE: The selection of PGW-C+SMF in the correct 5GC slice requires the same mapping between EPC and 5GC slices as required for single-access PDU sessions. In order to select an ATSSS capable PGW-C+SMF it is assumed that the operator deployment ensures that all PGW-C+SMF(s) configured to support the specific APN in this network slice are also capable to support ATSSS. There is however no assumption that all PGW-U+UPFs need to support ATSSS, since PGW-C+SMF can make a selection of PGW-U+UPF taking the multi-access properties into account. - The PGW-C+SMF determines based its capabilities whether the request can be accepted. The PCF decides whether the multi-access connectivity is allowed or not based on operator policy and subscription data, as described in clause 4.22.2. The PGW-C+SMF provides the following information via the APCO in the Create Session Response message to the ePDG: - An indication whether the request for using the PDN Connection for MA-PDU Session is accepted or not. - If the UE has indicated that it is capable of supporting the MPTCP functionality and the PGW-C+SMF accepts to activate the MPTCP functionality, then the network provides MPTCP proxy information to the UE, as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. - If the UE has indicated that it is capable of supporting the MPQUIC functionality and the PGW-C+SMF accepts to activate the MPQUIC functionality, then the network provides MPQUIC proxy information to the UE, as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. - UE Measurement Assistance Information (as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). - ATSSS rules - The ePDG forwards the received above information to the UE via IKE signalling. After the PDN Connection establishment: - If the UE registers to 5GC and wants to add 3GPP user-plane resources, then the UE shall send a PDU Session Establishment Request over this access containing a "MA PDU Request" indication as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When the UE wants to request a new MA PDU Session in 5GC/3GPP access, the description in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], applies. After the MA PDU Session establishment in 5GC/3GPP access, the description in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], applies with the following additions: - If the UE is registered to EPC and wants to add user-plane resources on non-3GPP access over EPC, then the UE shall send a PDN Connection Establishment Request over this access containing the IP address of the MA PDU Session in CFG_REQUEST Configuration Payload and include a "MA PDU Request" indication and UE's ATSSS capabilities and the PDU Session ID of the existing MA PDU Session on 3GPP access over 5GC. The ePDG forwards the ATSSS information via the APCO in the Create Session Request message to the PGW-C/SMF. - When the UE deregisters from the EPC/non-3GPP access (but remains registered on the 5GC/3GPP access), the ePDG will notify the PGW-C+SMF that the PDN Connection is released, as described in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26]. The SMF can then notify the UPF that the access type has become unavailable. A UE that has an established MA-PDU session over 3GPP access in 5GC and non-3GPP access in EPS, may be able to use Dual Connectivity for the 3GPP access leg. Depending on the RAT types supported by the UE, the PDU Session may also be handed over to 3GPP access in EPC. For a UE supporting both E-UTRAN/EPC access and NG-RAN/5GC access, the user plane resources for 3GPP access may be moved between E-UTRAN/EPC access and NG-RAN/5GC access as described in clause 5.17.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. For the MA PDU session over 3GPP access in 5GC and non-3GPP access in EPS, when a UE moves from NG-RAN/5GC to E-UTRAN/EPC, the SMF+PGW-C may release the user plane resources either over 3GPP access or non-3GPP access based on operator policy. In this case, while the UE remains in EPC in both 3GPP access and non-3GPP access, the UE shall not trigger PDN Connection establishment to add an additional EPC access leg to the MA PDU Session. If the SMF+PGW-C does not release the user plane resources over one of accesses, the UE sends traffic over both accesses based on ATSSS rules.