A transmission node in a wireless communication network includes a buffer, a transmitting section, a data processing section, a re-transmit queue, and a control section. To avoid duplication of SDUs for re-transmission, PDUs transformed from SDUs by the data processing section are maintained in the buffer by the control section after being transmitted to a mobile node in the network by the transmitting section. Addresses of the SDUs and associated sequence numbers are stored in the re-transmit queue. When handover of the mobile node from the transmission node to another transmission node occurs, PDUs of which the addresses are stored in the re-transmit queue are reverse transformed to SDUs with the associated sequence numbers so that the SDUs can be handed over to another transmission node.