1. 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.', '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.

2. 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, the base station controller configured to transmit information to the mobile station via the plurality of radio base stations during a diversity handover, wherein the system comprises:
a layer-3-cipherer configured to encipher and decipher layer 3 or higher layer information in an OSI reference model or an equivalent model; and
a layer-2-mutual-notifier residing on layer 2 of an OSI reference model or an equivalent model to communicate between different devices about an onset of transmission of enciphered information, and further wherein
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-3-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.', '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, the base station controller configured to transmit information to the mobile station via the plurality of radio base stations during a diversity handover, wherein the system comprises:', 'a layer-3-cipherer configured to encipher and decipher layer 3 or higher layer information in an OSI reference model or an equivalent model; and', 'a layer-2-mutual-notifier residing on layer 2 of an OSI reference model or an equivalent model to communicate between different devices about an onset of transmission of enciphered information, and further wherein', '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-3-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.

3. 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, the base station controller configured to transmit information to the mobile station via the plurality of radio base stations during a diversity handover, the system further comprising:
a layer-3-cipherer configured to encipher and decipher layer 3 or higher layer information in an OSI reference model or an equivalent model;
a retransmission control information adder residing on layer 2 of the OSI reference model or the equivalent model to add retransmission control information to information which has been enciphered by the layer-3-enciphering-means; and
a transmitter configured to transmit the enciphered information with the retransmission control information to the mobile station via the plurality of radio base stations, wherein
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 indication returned from the mobile station in reply to the start encipherment indication, and
the layer-3-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.', '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, the base station controller configured to transmit information to the mobile station via the plurality of radio base stations during a diversity handover, the system further comprising:', 'a layer-3-cipherer configured to encipher and decipher layer 3 or higher layer information in an OSI reference model or an equivalent model;', 'a retransmission control information adder residing on layer 2 of the OSI reference model or the equivalent model to add retransmission control information to information which has been enciphered by the layer-3-enciphering-means; and', 'a transmitter configured to transmit the enciphered information with the retransmission control information to the mobile station via the plurality of radio base stations, wherein', '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 indication returned from the mobile station in reply to the start encipherment indication, and', 'the layer-3-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.', '4. A method for a mobile communication system, which comprises 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, the method comprising:
receiving at the base station controller information from the switching center;
transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;
receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;
responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, the information from the switching center;
transmitting, at the base station controller, the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and
only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', 'receiving at the base station controller information from the switching center;', 'transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;', 'receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;', 'responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, the information from the switching center;', 'transmitting, at the base station controller, the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and', 'only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', '5. A method for a mobile communication system, which comprises a mobile station configured to conduct diversity reception, a plurality of radio base stations, and a base station controller communicating via the plurality of radio base stations under control of a switching center, the method comprising:
enciphering and deciphering layer 2 or higher layer information in an OSI reference model or an equivalent model;
transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;
receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;
responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;
transmitting at the base station controller the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and
only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', 'enciphering and deciphering layer 2 or higher layer information in an OSI reference model or an equivalent model;', 'transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;', 'receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;', 'responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;', 'transmitting at the base station controller the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and', 'only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', '6. A method for a mobile communication system, which comprises a mobile station configured to conduct diversity reception, a plurality of radio base stations, and a base station controller communicating via the plurality of radio base stations under control of a switching center, the method comprising:
enciphering and deciphering layer 3 or higher layer information in an OSI reference model or equivalent model;
using a layer 2 notifier residing on layer 2 of an OSI reference model or an equivalent model to communicate between different devices about an onset of transmission of enciphered information;
transmitting, at the base station controller, a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;
receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;
responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;
transmitting, at the base station controller, the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and
only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', 'enciphering and deciphering layer 3 or higher layer information in an OSI reference model or equivalent model;', 'using a layer 2 notifier residing on layer 2 of an OSI reference model or an equivalent model to communicate between different devices about an onset of transmission of enciphered information;', 'transmitting, at the base station controller, a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;', 'receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;', 'responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;', 'transmitting, at the base station controller, the enciphered information to the mobile station via the plurality of radio base stations during a diversity handover; and', 'only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', '7. A method for a mobile communication system, which comprises a mobile station configured to conduct diversity reception, a plurality of radio base stations, and a base station controller communicating via the plurality of radio base stations under control of a switching center, the method comprising:
enciphering and deciphering layer 3 or higher layer information in an OSI reference model or an equivalent model;
adding retransmission control information to the enciphered information at layer 2 of an OSI reference model or an equivalent model;
transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;
receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;
responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;
transmitting, at the base station controller, the enciphered information with the retransmission control information to the mobile station via the plurality of radio base stations during a diversity handover; and
only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', 'enciphering and deciphering layer 3 or higher layer information in an OSI reference model or an equivalent model;', 'adding retransmission control information to the enciphered information at layer 2 of an OSI reference model or an equivalent model;', 'transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment;', 'receiving, at the base station controller, a start encipherment response returned from the mobile station in reply to the start encipherment indication;', 'responsive to transmitting the start encipherment indication to the mobile station and before receiving the start encipherment response, becoming set to encipher, at the base station controller, information from the switching center;', 'transmitting, at the base station controller, the enciphered information with the retransmission control information to the mobile station via the plurality of radio base stations during a diversity handover; and', 'only after receiving the start encipherment response from the mobile station, becoming set to decipher, at the base station controller, information received from the mobile station via the plurality of radio base stations during the diversity handover.', '8. A mobile communication system comprising:
a mobile station;
a plurality of radio base stations connectible to the mobile station for communication;
a base station controller configured to send information to the plurality of radio base stations; and
a switching center configured to send information to the base station controller,
wherein the switching center comprises a mutual notifier configured to communicate an onset timing of transmission of enciphered information to both the mobile station and the plurality of radio base stations,
wherein the base station controller comprises
a controller-receiver configured to receive unciphered information from the switching center,
an encipherer configured to encipher the unciphered information received by the controller-receiver, and
a controller-transmitter configured to transmit to the plurality of radio base stations the enciphered information generated by the encipherer,

wherein the plurality of radio base stations each comprise
a base-station-receiver configured to receive the enciphered information from the base station controller, and
a base-station-transmitter configured to transmit a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment and, after transmitting the start encipherment indication to the mobile station, transmit to the mobile station the enciphered information received by the base-station-receiver, and

wherein the mobile station comprises
a mobile-station-receiver configured to receive multiple sets of the enciphered information transmitted from the plurality of radio base stations,
a diversity combiner configured to diversity-combine the multiple sets of the enciphered information received by the mobile-station-receiver,
a mobile-station-transmitter configured to return a start encipherment response in reply to the start encipherment indication;
a decipherer configured to become set, after receiving the start encipherment indication and before returning the start encipherment response, to decipher the enciphered information diversity-combined by the diversity combiner, and
an encipherer configured to become set, only after returning the start encipherment response, to encipher information transmitted to the plurality of radio base stations.', 'a mobile station;', 'a plurality of radio base stations connectible to the mobile station for communication;', 'a base station controller configured to send information to the plurality of radio base stations; and', 'a switching center configured to send information to the base station controller,', 'wherein the switching center comprises a mutual notifier configured to communicate an onset timing of transmission of enciphered information to both the mobile station and the plurality of radio base stations,', 'wherein the base station controller comprises
a controller-receiver configured to receive unciphered information from the switching center,
an encipherer configured to encipher the unciphered information received by the controller-receiver, and
a controller-transmitter configured to transmit to the plurality of radio base stations the enciphered information generated by the encipherer,', 'a controller-receiver configured to receive unciphered information from the switching center,', 'an encipherer configured to encipher the unciphered information received by the controller-receiver, and', 'a controller-transmitter configured to transmit to the plurality of radio base stations the enciphered information generated by the encipherer,', 'wherein the plurality of radio base stations each comprise
a base-station-receiver configured to receive the enciphered information from the base station controller, and
a base-station-transmitter configured to transmit a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment and, after transmitting the start encipherment indication to the mobile station, transmit to the mobile station the enciphered information received by the base-station-receiver, and', 'a base-station-receiver configured to receive the enciphered information from the base station controller, and', 'a base-station-transmitter configured to transmit a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment and, after transmitting the start encipherment indication to the mobile station, transmit to the mobile station the enciphered information received by the base-station-receiver, and', 'wherein the mobile station comprises
a mobile-station-receiver configured to receive multiple sets of the enciphered information transmitted from the plurality of radio base stations,
a diversity combiner configured to diversity-combine the multiple sets of the enciphered information received by the mobile-station-receiver,
a mobile-station-transmitter configured to return a start encipherment response in reply to the start encipherment indication;
a decipherer configured to become set, after receiving the start encipherment indication and before returning the start encipherment response, to decipher the enciphered information diversity-combined by the diversity combiner, and
an encipherer configured to become set, only after returning the start encipherment response, to encipher information transmitted to the plurality of radio base stations.', 'a mobile-station-receiver configured to receive multiple sets of the enciphered information transmitted from the plurality of radio base stations,', 'a diversity combiner configured to diversity-combine the multiple sets of the enciphered information received by the mobile-station-receiver,', 'a mobile-station-transmitter configured to return a start encipherment response in reply to the start encipherment indication;', 'a decipherer configured to become set, after receiving the start encipherment indication and before returning the start encipherment response, to decipher the enciphered information diversity-combined by the diversity combiner, and', 'an encipherer configured to become set, only after returning the start encipherment response, to encipher information transmitted to the plurality of radio base stations.', '9. The mobile communication system according to claim 8, wherein
the base station controller further comprises a retransmission control information adder configured to add retransmission control information to the unciphered information, and
the encipherer of the base station controller enciphers the unciphered information added with the retransmission control information.', 'the base station controller further comprises a retransmission control information adder configured to add retransmission control information to the unciphered information, and', 'the encipherer of the base station controller enciphers the unciphered information added with the retransmission control information.', '10. A mobile communication method implemented in a mobile communication system comprising a mobile station, a plurality of radio base stations connectible to the mobile station for communication, a base station controller configured to send information to the plurality of radio base stations, and a switching center configured to send information to the base station controller, the method comprising:
communicating, by the switching center, an onset timing of transmission of enciphered information to both the mobile station and the plurality of radio base stations;
receiving, by the base station controller, unciphered information from the switching center;
enciphering the unciphered information by the base station controller;
transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment before transmitting the start encipherment indication to the mobile station;
transmitting, by the base station controller, the enciphered information to the plurality of radio base stations;
receiving, by the plurality of radio base stations, the enciphered information from the base station controller;
transmitting, by the plurality of radio base stations, the enciphered information to the mobile station;
receiving, by the mobile station, multiple sets of the enciphered information transmitted from the plurality of radio base stations;
diversity-combining the multiple sets of the enciphered information by the mobile station;
returning, at the mobile station, a start encipherment response in reply to the start encipherment indication;
becoming set to decipher, at the mobile station, the diversity-combined, enciphered information after receiving the start encipherment indication and before returning the start encipherment response; and
only after returning the start encipherment response, becoming set to encipher information transmitted to the plurality of radio base stations.', 'communicating, by the switching center, an onset timing of transmission of enciphered information to both the mobile station and the plurality of radio base stations;', 'receiving, by the base station controller, unciphered information from the switching center;', 'enciphering the unciphered information by the base station controller;', 'transmitting at the base station controller a start encipherment indication to the mobile station to notify the mobile station of a start of encipherment before transmitting the start encipherment indication to the mobile station;', 'transmitting, by the base station controller, the enciphered information to the plurality of radio base stations;', 'receiving, by the plurality of radio base stations, the enciphered information from the base station controller;', 'transmitting, by the plurality of radio base stations, the enciphered information to the mobile station;', 'receiving, by the mobile station, multiple sets of the enciphered information transmitted from the plurality of radio base stations;', 'diversity-combining the multiple sets of the enciphered information by the mobile station;', 'returning, at the mobile station, a start encipherment response in reply to the start encipherment indication;', 'becoming set to decipher, at the mobile station, the diversity-combined, enciphered information after receiving the start encipherment indication and before returning the start encipherment response; and', 'only after returning the start encipherment response, becoming set to encipher information transmitted to the plurality of radio base stations.']