Disclosed is a method performed by a UE device that routes traffic to a 5G Core Network. The method includes receiving a first ATSSS rule including first traffic descriptor information and first steering mode information that identifies a first 3GPP access network operated by a first MNO, and a second ATSSS rule including second traffic descriptor information and second steering mode information that identifies a second 3GPP access network operated by the first MNO or a second MNO; transmitting a first type of traffic corresponding to the first traffic descriptor information included in the first ATSSS rule to the first 3GPP access network operated by the first MNO; and transmitting the first type of traffic or a second type of traffic corresponding to the second traffic descriptor information included in the second ATSSS rule to the second 3GPP access network operated by the first MNO or the second MNO.