COMMUNICATION SYSTEM, MASTER STATION DEVICE, AND COMMUNICATION CIRCUIT CHANGEOVER METHOD

PROBLEM TO BE SOLVED: To reduce frame losses at redundancy switching time and make uninterruptible switching possible, thereby providing a communication system which is free of service disconnection and is, therefore, higher in reliability than ever.SOLUTION: A communication system according to the present invention forms a communication path between slave station devices and a host network via a master station device by using one of a first communication circuit and a second communication circuit selectively. This communication system includes a discovery processing unit which executes a discovery process for detecting plural slave station devices connected to the master station device; a circuit switching unit which switches a communication circuit to form the communication path from the first communication circuit to the second communication circuit or vice versa; and a timing control unit which controls the timing with which the discovery processing unit executes a discovery process and the timing with which the circuit switching unit switches a communication circuit which forms the communication path from one to another by correlating those timings to each other.