data transmission system in mobile communication system

PURPOSE: A system for transmitting data in a mobile communication system is provided to enable a packet data convergence protocol to use a header compression method by an ROHC(Robust Header Compression) unit as well as to receive a bidirectional communication service from a radio link control layer, thereby supporting transmission of real-time packet data. CONSTITUTION: One radio link control entity located in a radio link control layer is connected with an ROHC entity located in a packet data convergence protocol layer, consisting of a transmitting unit and a receiving unit for transmission and receiving. Two unilateral radio link control entities perform transmission and receiving radio connection control functions, respectively, and supply a bidirectional data transmission service in connection with the ROHC entity.