A method of registering an optical network unit (ONU) in an optical line terminal (OLT). The OLT determines a lane to be used by the ONU based on a transmission rate supported by the ONU, combines or distributes data of a dataflow based on a rate of the lane by comparing the rate of the lane to a rate of the dataflow of a media access control (MAC) client interface, and, when the OLT and the ONU are connected through multiple lanes, transmits and receives data between the OLT and the ONU through channel bonding for more effective use of a network.