Method of packet reordering and packet retransmission

The present invention relates to relates to a wireless communication system, a method for packet reordering reliable data transfer during handover and the packet transmission method. To reorder the PDCP packets for reliable data transfer in the case of performing a handover in a broadband wireless access system, a method for transmitting a packet from the serving BS, the method comprising a said step of receiving one or more packets from the host weigh in the last packet of the packet comprises, and one or more of the steps of sequentially transmitted to the target base station over the packet it is characterized in that it comprises an information field indicating the last packet or not. When the UE performs an I-RAT handover, in advance, by reordering PDU from the base station of the target packet according to embodiments of the present invention transfer to the terminal, it is possible to fast data transmission without the need for re-ordering of packets at the terminal.