COMMUNICATION DEVICE, COMMUNICATION SYSTEM, AND COMMUNICATION METHOD

摘要

Provided are a communication device, a communication system, and a communication method which can automatically recover the function as a communication system by processes of respective communication devices if a failure has occurred in a communication between the communication devices connected in series. When a communication is performed by specifying the upstream and the downstream in the order of relay devices (3a, 3b, 3c, 3d), a KeepAlive message is transmitted to show that each executes an effective communication.  When the relay device (3a) detects a failure by that the KeepAlive message cannot be received from the relay device (3b), the relay device (3a) transmits a KeepAlive message containing the report that the failure has been detected.  Upon reception of the KeepAlive message containing the failure information, the relay device (3b) detects a failure at the upstream side, modifies the communication path, and transmits a master candidate report to the relay device (3c) at the downstream side so that the relay device (3b) itself becomes a master.