Section: 4.22.2.4 MA PDU Session establishment with non-3GPP access connected to EPC and 3GPP access connected to 5GC 4.22.2.4.1 General
Content: This clause applies to the case where, for a PDU Session, multi-access connectivity via both EPC (over non-3GPP access) and 5GC (over 3GPP access) is supported and allowed in the UE and network. In this case, multi-access connectivity using ATSSS via both non-3GPP access to EPC and 3GPP access to 5GC may be provided as described in this clause. For this scenario, the general principles for ATSSS as described in clause 5.32 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] apply, with the additions provided in this clause 4.22.2.3. A Multi-Access PDU Session may be extended with user-plane resources via an associated PDN Connection on non-3GPP access in EPC. This enables a scenario where a MA PDU Session can simultaneously be associated with user-plane resources on non-3GPP access network connected to EPC and 3GPP access connected to 5GC. Such a PDN Connection in EPS would thus be associated with multi-access capability in the UE and PGW-C+SMF. NOTE: To the MME and SGW this is a regular PDN Connection and the support for ATSSS is transparent to MME and SGW. The UE may operate in either single-registration mode or dual-registration mode in 3GPP access. Irrespective of whether the UE operates in single-registration mode or dual-registration mode in 3GPP access, it is assumed that the UE supports simultaneous registrations for 3GPP access in 5GC and non-3GPP access in EPC. The ATSSS rules are provided from the PGW-C+SMF to the UE via SM NAS signalling over 5GC, as described in clause 5.32.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. ATSSS rules may be provided via the EPC. After the establishment of a MA PDU Session and setting up user-plane resources in non-3GPP access in EPC and 3GPP access in 5GC, the UE distributes the uplink traffic across the two access networks as described in clause 5.32.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. Similarly, the PDU Session Anchor UPF performs distribution of downlink traffic across the two access networks as described in clause 5.32.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. The PMF protocol may be used via any user plane connection, i.e. via non-3GPP access in EPC or 3GPP access in 5GC. The PCF functionality to support ATSSS, as described in clause 5.32.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] and TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [20] applies also in the case of interworking with EPC.