A method of transmitting downlink data after re-establishment of a universal terrestrial radio access network (UTRAN) acknowledged mode (AM) radio link control (RLC) entity includes receiving a plurality of RLC service data units (SDUs) from a packet data convergence protocol (PDCP) layer of the UTRAN; dividing the received RLC SDUs into RLC protocol data units (PDUs) and transmitting the RLC PDUs to a user equipment (UE); receiving acknowledgments from the UE for received RLC PDUs; receiving a re-establishment request at a transmitting side of the AM RLC entity from upper layers of the UTRAN; discarding all RLC SDUs that have been fully transmitted to the UE before the re-establishment request is received; and discarding all RLC SDUs that have not been fully transmitted to the UE when the re-establishment request is received.