Patent ID: 8260298

Claim:
A method of preventing call drop in a mobile terminal when a serving radio network subsystem SRNS relocation to a target RNC from a source RNC is performed, the method comprising: receiving a control message in accordance with start of the SRNS relocation from the target RNC; performing a RLC configuration procedure; transmitting a complete message in accordance with the RLC configuration procedure to the target RNC; receiving a RLC RESET message from the target RNC when an exceptional case occurs after the complete message is transmitted; and retransmitting the complete message to the target RNC in accordance with the received RLC RESET message, wherein the exception case includes at least one of, a case that a message having an undesired serial number is delivered between the mobile terminal and the target RNC, a case that the target RNC does not receive a normal ACK from the mobile terminal in response to unidentified data transmitted from the source RNC before the SRNS relocation is started, a case that the target RNC receives a NACK, a case that the mobile terminal does not receive a normal ACK from the target RNC in response to unidentified data transmitted from the source RNC before the SRNS relocation is started, and a case that the mobile terminal receives a NACK.