| 摘要 |
PURPOSE:To quicken a control processing and to improve the reliability by controlling a frame header control device and a loopback path selection circuit if the receptions of each of a center node and local nodes are in error so as to remove a faulty location and to form a path giving loopback to an information signal. CONSTITUTION:If loops A, B are opened as shown in caption C, synchronization step-out caused by the fault of the loop A is detected, a photoelectric conversion circuit 2A and loop control information connect a loopback path selection circuit 3B, a photoelectric conversion circuit 1B and a loopback path selection circuit 3A, and a loopback command signal is sent sequentially to each node from a node 14 closest to the faulty position of the loop A. The loopback command signal is returned to the center node 10 and when the frame synchronization is kept, the connection of loopback is released sequentially in each node. This is applied also similarly to the loop B, since the center node 10 for supervisory control connects the transmission line of the loops A, B, the photoelectric conversion circuits 1B, 2B are connected to form entirely one closed loop transmission line.
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