Patent ID: 8811336

Claim:
A method of performing a handover procedure at a source base station in a mobile communication system, the method comprising: transmitting, by the source base station, a first message to a target base station after a handover determination to the target base station is made; receiving, at the source base station, a second message, from the target base station, in response to the first message; and transmitting, by the source base station, a handover command message to a user equipment (UE) after the second message is received, wherein the first message includes data transmission and reception state information including a time duration while the UE has not transmitted data to the source base station or has not received data from the source base station before the handover, wherein the data transmission and reception state information further includes a discontinuous reception (DRX) parameter setup value used lastly by the UE and a plurality of DRX setup values set in the UE, wherein the first message is directly transmitted through an interface between the source base station and the target base station, and wherein the second message includes a UE identity and resource configuration information.