| 摘要 |
PURPOSE:To attain the changeover of present use/spare where the deterioration in a transmission circuit is discriminated correctly by controlling the changeover of the transmission circuit by an error rate of a reproduced output. CONSTITUTION:An optical signal separated by an optical separating circuit 9 of the transmission circuit is converted into an electric signal by a photodetector 10, discriminated by a discriminator 11-2 and inputted to one input of a comparator 12. An output of a discriminator 3 is inputted to another input of the comparator 12. If the transmission circuit is not operated normally, since an input digital signal is not reproduced correctly, an output representing dissidence appears at the comparator 12. A counter 12 resets this output for each prescribed period and counts it, and when the result of count exceeds a prescribed number of times, this output is transmitted to a switching circuit 5 to changeover the transmission circuit from the present use line into the spare line. |
