| 摘要 |
PURPOSE:To quicken the recovery of a communication system by providing a means detecting that the reception signal of one transmission system is normal and the reception signal of other transmission line system is not normal and using a changeover means to set the branch of the signal. CONSTITUTION:A loopback control section 40 inputs the detection signal of frame synchronizing detection circuits 4, 14 and controls switches 5, 15, 21 so as to branch a signal received from a normal system to the transmission side of the abnormal system when the state that only one transmission line system is normal continues for a prescribed time. That is, the loopback control section 40 discriminates that the state that a synchronizing detection signal is received from, e.g., the circuit 4 and no synchronizing detection signal is obtained from the circuit 14 continues for a prescribed time, the section 40 constitutes the loopback from the system 0 to the system 1 by setting the switches 5, 15 to the position R and the switch 21 to the position L.
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