Patent ID: 7970405

Claim:
A method of transmitting data in a handover between a serving base station and a target base station in a wireless communication system, the method comprising: causing the serving base station to determine a handover of a mobile terminal and transmit a handover request message including information on the target base station to a gateway; receiving a first handover request message including information on a target base station from the serving base station; transmitting a second handover request message including multicast group information to the target base station based on the first handover request message; joining the target base station into an existing multicast group subsequent to receiving a message that includes the multicast group information that is updated by including the information on the target base station; causing the serving base station to receive a handover command message informing that handover preparation processes of the mobile terminal have been performed from the gateway and transmit a base station context data message to the target base station; receiving a handover response message from the target base station that has been joined into the multicast group transmitting data traffic to the serving base station and the target base station; and receiving a handover completion message from the target base station, the handover completion message informing that a handover of a mobile terminal is completed from the serving base station to the target base station included in the updated multicast group information; and transmitting the data traffic to the mobile terminal through the target base station.