| 摘要 |
A transmission path back-up system according to the invention has a multiplexer for dividing a set of time slots on a digital private line into a first set of time slots to accommodate the group of signals to be backed up and a second set of time slots to accommodate the group of signals not to be backed up. A selector sends out these multiplexed signals on the digital private line as transmission path when the digital private line is in a normal state, or selectively extracts the group of signals to be backed up and sends them out to an exchange line when the digital private line is in trouble. The back-up system makes it possible to realize an economical and yet reliable network which can extract and send out to the back-up ISDN line only the set of time slots for the group of signals to be backed up when the private line is in trouble.
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