| 摘要 |
PURPOSE:To effectively utilize a line by providing a transmission line switching circuit and a loopback circuit applying tentatively loopback at the reception of optical transmission stop signal to an optical transmission line changeover device. CONSTITUTION:Assuming that an open wire fault of an optical fiber takes place at a point E of an active line A2 connecting optical intermediate repeaters 91, 92, then an optical transmission stop signal is sent to an optical transmission line changeover device 71 via the optical intermediate repeater 91 and an optical terminal station repeater 81 if an optical transmission line B2 to an opposite station side is not faulty. This signal is detected by an optical transmission line changeover device 71, then loopback is applied tentatively by a loopback circuit 73 and the result is inputted to an optical input port of the optical intermediate repeater 92. Thus, it is discriminated that no open wire fault takes place in the optical transmission line B2 to the opposite station, that is, the optical intermediate repeater 91. On the other hand, the optical transmission stop signal is inputted from the optical input in the optical intermediate repeater 91 of the opposed station, it is detected by a detection circuit and a control circuit stops the optical output of an electrooptic signal conversion circuit. |
