| 摘要 |
PURPOSE:To monitor the state of a line in an in-service state, by adjusting a time difference between error detection codes generated respectively on a transmission and a reception sides by a varying means, when the coincidence of them is detected. CONSTITUTION:The transmission signal of terminal 2 is transmitted to a terminal 3 by a digital line 1 via a communication network. An error detection circuit 5 in a customer line termination device 4 on the transmission side performs code error detection at every prescribed bit length, and transmits the error detection code to the reception side. An error detection circuit 7 in the customer line termination device 5 performs code error detection for a received transmission signal at every bit length. Then, the error detection code is generated. By adjusting the time difference between the error detection signal generated respectively on the transmission and the reception sides by the varying means, coinciding their timings, then comparing them, the output of a compared result is sent out to a terminal 8.
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