Method of packet reordering and packet retransmission

A method of transmitting reordered packets at a target base station in case of a mobile station performing handover, the method comprising:

• receiving a series of first packets sequentially from a serving base station, wherein a first packet of the series of first packets includes an information field indicating whether the first packet is last transmitted;
• receiving a series of second packets sequentially from an upper layer entity;
• reordering an order of the received packets;
• transmitting the reordered packets to the mobile station;
• receiving a reception status message regarding the transmitted reordered packets from the mobile station, the reception status message including a bitmap field and a starting sequence number field, the bitmap field indicating whether an error of the transmitted reordered packets is detected in order from a last transmitted packet to a first transmitted packet, the starting sequence number field indicating a sequence number of a next packet to be transmitted by the target base station;
• and
• retransmitting at least one error-detected packet to the mobile station according to the reception status message.