A method used for a user equipment, UE, for distributing uplink data flow between different access networks in a fifth generation, 5G, communication system, the method comprising: maintaining an Access Traffic Steering, Switching, and Steering, ATSSS, rules table; receiving a request to establish an uplink data flow to a data network, DN,; determining from the ATSSS rule table whether the DN is in the ATSSS rule table in response to receiving the request to establish the uplink data flow to the DN; selecting a first packet data unit, PDU, session from the ATSSS rule table for the uplink data flow to the DN in response to having been determined that the DN is in the ATSSS rule table; and creating a second PDU session for the uplink data flow to the DN and recording the second PDU session in the ATSSS rule table in response to having been determined that the DN is not in the ATSSS rule table, whereby the first PDU session is a multiple access PDU, MA-PDU, session which distributes the uplink data flow into a first access network and a second network by selecting a steer mode among a plurality of steering modes; the method further being characterized by comprising: receiving a request to switch the uplink data flow to the data network, DN, from a first type of access network to a second type of access network; determining from the ATSSS rule table whether the second type of access network is already linked with the DN according to the ATSSS rule table in response to receiving the request to switch the uplink data flow to the second type of access network; selecting a third packet data unit, PDU, session which belongs to the second type of access network from the ATSSS rule table for the uplink data flow to the DN in response to having been determined that second type of access network is already linked with the DN according to the ATSSS rule table; and creating a fourth PDU session for the uplink data flow to the DN and recording the forth PDU session in the ATSSS rule table in response to having been determined that second type of access network is not linked with the DN according to the ATSSS rule table. maintaining an Access Traffic Steering, Switching, and Steering, ATSSS, rules table; receiving a request to establish an uplink data flow to a data network, DN,; determining from the ATSSS rule table whether the DN is in the ATSSS rule table in response to receiving the request to establish the uplink data flow to the DN; selecting a first packet data unit, PDU, session from the ATSSS rule table for the uplink data flow to the DN in response to having been determined that the DN is in the ATSSS rule table; and creating a second PDU session for the uplink data flow to the DN and recording the second PDU session in the ATSSS rule table in response to having been determined that the DN is not in the ATSSS rule table, whereby the first PDU session is a multiple access PDU, MA-PDU, session which distributes the uplink data flow into a first access network and a second network by selecting a steer mode among a plurality of steering modes; the method further being characterized by comprising: receiving a request to switch the uplink data flow to the data network, DN, from a first type of access network to a second type of access network; determining from the ATSSS rule table whether the second type of access network is already linked with the DN according to the ATSSS rule table in response to receiving the request to switch the uplink data flow to the second type of access network; selecting a third packet data unit, PDU, session which belongs to the second type of access network from the ATSSS rule table for the uplink data flow to the DN in response to having been determined that second type of access network is already linked with the DN according to the ATSSS rule table; and creating a fourth PDU session for the uplink data flow to the DN and recording the forth PDU session in the ATSSS rule table in response to having been determined that second type of access network is not linked with the DN according to the ATSSS rule table. receiving a request to switch the uplink data flow to the data network, DN, from a first type of access network to a second type of access network; determining from the ATSSS rule table whether the second type of access network is already linked with the DN according to the ATSSS rule table in response to receiving the request to switch the uplink data flow to the second type of access network; selecting a third packet data unit, PDU, session which belongs to the second type of access network from the ATSSS rule table for the uplink data flow to the DN in response to having been determined that second type of access network is already linked with the DN according to the ATSSS rule table; and creating a fourth PDU session for the uplink data flow to the DN and recording the forth PDU session in the ATSSS rule table in response to having been determined that second type of access network is not linked with the DN according to the ATSSS rule table.