METHOD OF SWITCHING APPARATUS, COMMUNICATION CONTROL UNIT, AND COMMUNICATION SYSTEM

PROBLEM TO BE SOLVED: To make a switching between apparatuses for current use and for emergency use, with the operation being continued without missing of signals or interruption of communication services, even if such a protocol is used where resend function and busy state are not specified. SOLUTION: From the start to the finish of switching, maintenance equipment 6 periodically sends broadcast signals to a communication control unit 1 for current use and a communication controlling unit 2 for emergency use. When the communication control unit 1 for current and the communication control unit 2 for emergency receive a first broadcast signal, a memory where the information about the executed signal processing is stored is copied from the communication controlling unit 1 to the communication controlling unit 2, while both of the communication controlling units accumulate inputted signals in queues inside the control units. When copying of the memory is finished, the communication control unit 1 asks the communication control unit 2 about the signal processing state, each time the broadcast signal is received. When the signal processing states of the two communication controlling units are synchronized, the communication control unit 1 is switched to the communication control unit 2.