5.32.7.3 Interworking without N26 Interface

Interworking without N26 interface is based on clause 5.17.2.3, with the following differences and clarifications:

• After UE moves from 5GS to EPS, UE may send a PDN Connectivity Request with "handover" indication to transfer the MA PDU Session to EPS. Then, if the UE or the network does not support MA PDU Session with 3GPP access connected to EPC, the SMF+PGW-C triggers to release MA PDU in 5GS. If UE does not transfer the MA PDU Session to EPS, UE keeps the MA PDU Session in 5GS and UE may report to UPF that 3GPP access is unavailable, all MA PDU Session traffic is transported over N3GPP access. Later, if UE returns to 5GS, UE may report the 3GPP access availability to UPF. If the UE and the network support MA PDU Session with 3GPP access connected to EPC, the UE includes a "handover" indication and a "MA PDU Request" indication as well as the PDU Session ID in the PCO and the SMF+PGW-C keeps the user-plane resources over non-3GPP access in 5GC as described in clause 4.22.6.2.5 of TS 23.502 [3].
• After UE moves from EPS to 5GS, UE may trigger PDU Session Establishment procedure to transfer the PDN Connection to 5GS. During the PDU Session Establishment procedure, if the PDN Connection was not used as the 3GPP access leg of the MA PDU Session, the UE may request to establish a MA PDU Session by including "MA PDU Request" or, if no policy in the UE (e.g. no URSP rule) and no local restrictions mandate a single access for the PDU Session, the UE may include the "MA PDU Network-Upgrade Allowed" indication.