| 摘要 |
PURPOSE:To attain the optical communication between communication stations by providing two bidirectional optical transmission means applying optical communication with a communication station adjacent to each communication station and using one of the two bidirectional optical transmission means if no optical communication is applied between adjacent communication stations. CONSTITUTION:If an optical fiber 3 between communication stations 20a and 20c is disconnected at a position C, since no acknowledgement signal (ACK) is sent to the communication station 20c, the station 20c recognizes the occurrence of a fault. In this case the communication station 20c sends an instruction signal to the communication stations 20b, 20a in the direction of arrow B so as to allow both the stations to send the ACK signal in a direction opposite to the direction B. In this case, since the ACK signal comes from both the stations, the communication station 20c recognizes the occurrence of a transmission line fault between the stations 20a and 20c. When the open fault is recognized in this way, the station 20c informs it to the stations 20a, 20b to disconnect the line between the stations 20a and 20c imaginarily and to change the network as a path shown in figure. |
