Section: 4.22.2.3.2 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 3GPP access in EPS using PDN Connection Establishment procedure. The UE provides via PCO to PGW-C+SMF the following information: - 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 the ATSSS-LL functionality, the MPTCP functionality, the MPQUIC functionality, or any combination of them). - The MME may select a PGW-C+SMF as described in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13] and clause 4.11.0a.4. NOTE 1: 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 in the PCO to the UE: - 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/or the MPQUIC functionality and the PGW-C+SMF accepts to activate the MPTCP functionality and/or the MPQUIC functionality, then the network provides MPTCP proxy information and/or 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]). After the PDN Connection establishment: - If the UE registers to 5GC and wants to add non-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]. NOTE 2: Adding the PDU Session connectivity and user plane resources over non-3GPP access in 5GS allows the PGW-C+SMF to provide ATSSS rules to the UE. When the UE wants to request a new MA PDU Session in 5GC/non-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 5GS/non-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 3GPP access over EPC, then the UE shall send a PDN Connection Establishment Request over this access containing a "handover" indication and include a "MA PDU Request" indication in the PCO as well as the PDU Session ID of the existing MA PDU Session on non-3GPP access over 5GC. - When the UE deregisters from the EPC access (but remains registered on the 5GC access), the MME will notify the PGW-C+SMF that the PDN Connection is released, as described in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13]. The SMF can then notify the UPF that the access type has become unavailable. In order to support EPS interworking when Ethernet type PDN Connection is not supported in EPS, the UE may use non-IP type PDN Connection when the UE establishes a PDN Connection in EPS as an added 3GPP access leg of an Ethernet type MA PDU Session. In this case, the UE and SMF shall locally associate the PDN Connection as an Ethernet type PDU Session as described in TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When Ethernet type PDN Connection is not supported in EPS, the UE does not request to establish a PDN Connection with "MA PDU Request" indication before the UE registers to 5GS and establishes MA PDU Session over non-3GPP access. A UE that has an established MA-PDU session over non-3GPP access in 5GC and 3GPP access in EPS, may be able to use EN-DC for the 3GPP access leg. Depending on the RAT types supported by the UE, the PDN connection may also be handed over to 3GPP access in 5GC. 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]. The PDU Session and User Plane resources active over non-3GPP access are not affected by such inter 3GPP access RAT change.