A method of establishing an extended IP flow in a wireless communication system can include establishing, at a user equipment (UE), an initial IP flow with a packet data network gateway (PDN-GW) included in an evolved packet core (EPC) through a first type access network and further establishing, at the UE, the extended IP flow with the PDN-GW through a second type access network different from the first type access network, while maintaining the initial IP flow with the PDN-GW through the first type access network, wherein a binding update is transmitted to the PDN-GW, wherein a binding acknowledgement is transmitted by the PDN-GW in response to the binding update if a single IP address is allocated to identify both the initial IP flow and the extended IP flow, and wherein the single IP address is included in the binding acknowledgement.