A method of handling multi-access (MA)
Protocol data unit (PDU) session establishment procedure for an MA PDU session already established with a 3GPP PDN leg is proposed. In one novel aspect, for a 5GS MA PDU session already established on 3GPP access via an EPS PDN connection, upon
receipt of a PDU SESSION ESTABLISHMENT ACCEPT message over non-3GPP access, the UE performs a local release of the MA PDU session if any value of at least one of the critical MA PDU session parameters, including the PDU session type, selected SSC mode, 5
GSM cause, PDU address, S-NSSAI, and DNN IEs in the PDU SESSION ESTABLISHMENT ACCEPT message is different-from / un-
sync / not-matched / not-compatible-with the corresponding stored value of the MA PDU session mapped from the (default EPS bearer of the) PDN connection. The UE also performs a
REGISTRATION procedure over non-3GPP access and a TAU procedure over 3GPP access.