A method of supporting data transmission of a network node in a wireless communication system includes: receiving downlink data from a Data Network (DN); encapsulating the downlink data with an IP address of an User Equipment (UE) based on whether the DN is an Internet Protocol (IP) based network or a non-IP based network; not encapsulating, if the DN is the IP based network, the received downlink data with the IP address of the UE and encapsulating, if the DN is the non-IP based network, the received downlink data with the IP address of the UE; and transmitting the downlink data encapsulated with the IP address or the downlink data that are not encapsulated with the IP address to an Access Network (AN).