Patent ID: 8275133

Claim:
A mobile communication system comprising: a mobile station configured to conduct diversity reception; a plurality of radio base stations; and a base station controller communicating with the mobile station via the plurality of radio base stations under control of a switching center, wherein the system comprises a layer-2-cipherer configured to encipher and decipher layer -2 or higher layer information in an OSI reference model or an equivalent model, the base station controller is configured to transmit the enciphered information to and receive deciphered information from the mobile station via the plurality of radio base stations during a diversity handover, the base station controller transmits a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment and receives a start encipherment response returned from the mobile station in reply to the start encipherment indication, and the layer-2-cipherer, responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response from the mobile station, becomes set to encipher information to be sent to the mobile station but becomes set to decipher information from the mobile station only after receiving the start encipherment response from the mobile station.