| 摘要 |
A digital exchange which can prevent its failure even when an abnormality takes place in one of digital trunks extracting clock signals from digital lines, so long as at least one of the digital trunks is normal, and also a method of controlling the digital exchange. A common transmission line is used for the clock signals extracted at the digital trunks, a synchronizing-signal generating circuit is provided for generating a synchronizing signal having a predetermined period with use of the clock signal received from one of the digital trunks through the common transmission line, and the clock extracting circuit in each of the digital trunks is provided with a circuit for sending the extracted clock signal from the digital line onto the transmission line in synchronism with the synchronizing signal. Further, a shift in frequency synchronization between the synchronizing clock provided to the time divisional switch and a frame synchronizing signal issued from the time divisional switch is detected and when the shift reaches to a predetermined level, its own synchronizing clock is sent to the time divisional switch.
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