Method for performing a handoff in a mobile communication system

A method for performing a handoff of a mobile terminal (MT) moving between cells of base transceiver stations (BTSs) in a mobile communication system including a plurality of BTSs, and a base station controller (BSC), the method comprising the steps of:

• if a target BTS is selected as a handoff candidate for the MT as the MT moves from a cell of a source BTS in service toward the target BTS, transmitting from the BSC a first message for requesting the target BTS to buffer packets, and transmitting packets to be transmitted to the MT to both the source BTS and the target BTS;
• upon receiving the first message in the target BTS, buffering packets received from the BSC;
• if the target BTS is determined as a serving BTS for the MT, transmitting from the BSC a second message for retrieving a last sequence number of a last packet transmitted to the MT, to the source BTS;
• transmitting from the source BTS a third message including the last sequence number to the BSC, in response to the second message;
• transmitting from the BSC a fourth message including the last sequence number acquired from the third message, to the target BTS;
• and
• transmitting packets with sequence numbers higher than the last sequence number to the MT.