Abstract: Code data of input type and output type low-speed interface units installed in one and other optical data transmission apparatus, placed opposite to and operatively connected to each other, are compared automatically in the one and the other optical data transmission apparatus respectively with code data of input type and output interface units in the other optical data transmission apparatus, sent from the other to the one optical data transmission apparatus and with code data of input type and output interface units in the one optical data transmission apparatus, sent from the one to the other optical data transmission apparatus.

Abstract: A transmission line switching system for switching a transmission line in operation to another transmission line when a fault occurs in the transmission line during operation comprising: a transmission line in operation constituted by a plurality of terminal repeaters, a plurality of circuit switching apparatuses, and a plurality of transmission cables, all connected in series; and another transmission line provided between a head terminal repeater and an end terminal repeater; wherein when a transmission cable is completely disconnected, information input from the head terminal repeater is returned from a terminal repeater located just before a disconnection in the transmission cable to the head terminal repeater, transferred from the head terminal repeater to the end terminal repeater through the another transmission line, returned from the end terminal repeater to a terminal repeater located just after the disconnection in the transmission cable, and returned to the end terminal repeater.

Abstract: A communication system includes a plurality of stations, a first working line coupling adjacent stations among the plurality of stations, a second working line passing predetermined stations among the plurality of stations without dropping therein, and a protection line provided in common for the first working line and the second working line, a supervisory signal always passing through the protection line. Each of the stations includes an internal circuit for receiving an input transmission signal from the first working line and sending an output transmission signal to the first working line.