Patent ID: 8705343

Claim:
A transmission station for double-ring networks including a plurality of transmission stations, each configured with a pair of communication ports for communications to be implemented bi-directionally, and mutually connected by said pairs of communication ports in a ring form through a transmission line to implement intercommunications between the transmission stations, comprising: means for periodically sending one or more transmission frames each containing specific information in a complete state of initialization; synchronization frame detecting means for detecting synchronization frames having specific information meeting set conditions from transmission frames through said pair of communication ports, respectively; no-synchronization frame detecting means for detecting no reception of said synchronization frames over a preset interval, from output signals of said synchronization frame detecting means, respectively; synchronization absence detecting means for detecting, under a condition that synchronization frames are received periodically through one of the communication ports, a state that synchronization frames are not received through the other of the communication ports over a preset interval; and reception anomaly detecting means for detecting anomalies in states of reception signals of transmission frames received through the communication ports, respectively, and wherein the transmission station serves as a terminal station fulfilling the following functions; the transmission station responds in accordance with information contained in a transmission frame received through one of the communication ports in which a no-synchronization detecting state is detected by the corresponding no-synchronization detecting means, and changes a state of the one of the communication ports to a blocked state that keeps the other of the communication ports from sending said transmission frame by relay from the one of the communication ports to the other of the communication ports; and the transmission station changes a state of one of the communication ports in which a reception anomaly detecting state is detected by the corresponding reception anomaly detecting means to a blocked state, thereby holding the communication ports of others of the plurality of transmission stations unblocked, during a period from a detection of failure occurrence to a recovery of network function recovery.