End station digital transmission link relieving system

An end station for a system for relieving a plurality of bidirectional digital data transmission working lines connected to two of the end stations of a digital transmission system including a plurality of bidirectional digital spare lines connected between said end stations, said end station comprising:

• means for detecting transmission faults on each of said working lines,
• means connected to said transmission fault detecting means for exchanging with another end station first and second order signals, the first order signals being exchanged on a selected free spare line in response to the detection of a transmission fault on a working line, and the second order signals being exchanged on said working line in response to the detecting means detecting a stop of said transmission fault on the working line,
• first switching means controlled by said order signal exchanging means for (a) connecting the order signal emitting means of said exchanging means to said spare line in response to said transmission fault being detected on said working line, (b) connecting (i) the emitting end of said working line to said spare line and (ii) said order signal emitting means to said working line in response to said first order signals, and (c) disconnecting said working line from said order signal emitting means in response to said second order signals, and
• second switching means controlled by said order signal exchanging means for (a) connecting the order signal receiving means of said exchanging means to said spare line in response to said transmission fault being detected on said working line, (b) connecting the receiving end of said working line to said spare line and holding a connection between said order signal receiving means and said spare line in response to said first order signals, (c) disconnecting said order signal receiving means from said spare line and for connecting said order signal receiving means to said working line in response to the transmission fault no longer being detected, and (d) disconnecting said working line from said order signal emitting means in response to said second order signals.

In combination, a digital transmission system including plural bidirectional digital data transmission working lines, plural bidirectional digital data transmission spare lines, and end stations connected to said working and spare lines, the working lines being relieved by the spare lines;

• each of the end stations comprising:
• means for detecting transmission faults on each of said working lines,
• means for selecting a free spare line in response to the detection of transmission faults on a working line,
• means for emitting digital order signals to the other end station,
• means for receiving digital order signals from said other end station,
• first and second switching means for connecting said order signal emitting and receiving means to a selected free spare line such that said order signal emitting and receiving means of said end stations exchange first order signals therebetween in response to the detection of a transmission fault on said working line, and for connecting the emitting and receiving ends of said faulty working line to said selected free spare line in response to said first order signals from said other end station,
• third switching means for connecting said order signal emitting means to said faulty working line such that said order signal emitting means transmits second order signals on said faulty working line in response to said first order signals from said other end station,
• fourth switching means for connecting said order signal receiving means to said working line in response to the transmission fault no longer being detected by the detecting means and said working line being repaired;
• said transmission fault detecting means controlling said first, second, third and fourth switching means in response to said second order signals received in said order signal receiving means such that emitting and receiving ends of said repaired working line are connected to said working line and are disconnected from said selected spare line;
• said order signal receiving means holding a connection to said selected spare line from a time at the start of exchange of said first order signals and up to just before the transmission fault on said working line is no longer being detected by the detecting means such that said order signal receiving means can receive order signals from said other end station on said selected spare line in response to a transmission fault which relates to another working line and which is detected in said other end station.