Abstract: An RNC server issues an encryption start instruction to a media gateway (MG) and a terminal. The MG and terminal, which have received the encryption start instruction, encrypt U-Plane information using a predetermined secret key, and adds a predetermined encryption start bit to the encrypted U-Plane information for transmission to a communication partner. The communication partner, upon detection of the encryption start information, decrypts the received U-Plane information using the predetermined secret key.

Abstract: An RNC server issues an encryption start instruction to a media gateway (MG) and a terminal. The MG and terminal, which have received the encryption start instruction, encrypt U-Plane information using a predetermined secret key, and adds a predetermined encryption start bit to the encrypted U-Plane information for transmission to a communication partner. The communication partner, upon detection of the encryption start information, decrypts the received U-Plane information using the predetermined secret key.

Abstract: In a system comprising a first base station (B1) assigned with a control channel frequency, a counterpart mobile station (P1) of the first base station, and a second base station (B2) adjacent to the first base station and assigned with the control channel frequency, the first base station comprises a control information transmitting portion (1, 5) for intermittently transmitting control information signals through the control channel frequency to the counterpart mobile station with a time duration left between two adjacent ones of the control information signals. A time duration determining portion (2, 14) randomly determines a following time duration between current and following control information signals so that the following time duration randomly varies from a previous time duration previously determined between the current and previous control information signals.