Communication in dual protocol environments

It is a communication apparatus provided with the 1st communications system (4) that transmits and/or receives a signal according to the 1st program, and the 2nd communications system (3) that transmits and/or receives a signal according to the 2nd protocol. As for the 2nd protocol, in it, a receiver (3) can direct that it is in a response impossible state in a transmitter (2), and the transmitter has a function in which data transmission to the receiver can be forbidden, when the receiver is in a response impossible state. The communication apparatus answers further a signal activity detector (9) which detects an activity of a signal of the 1st protocol, and the signal activity detector, and it has a control unit (7) made to direct that a self-system is in a response impossible state with the 2nd communications system.