A terminal includes a higher level bandwidth manager and a lower level bandwidth manager. The higher level bandwidth manager generates a guaranteed access request message including size information of a bandwidth corresponding to user data, transmits the guaranteed access request message, and transmits a user data transmission message including the user data. The lower level bandwidth manager uses the guaranteed access request message transmitted from the higher level bandwidth manager, generates a bandwidth request message using a guaranteed access, transmits the bandwidth request message to a base station, obtains the user data from the user data transmission message when receiving a bandwidth allocation signal from the base station, and transmits the user data to the base station.