Optical repeater monitoring system

An optical repeater monitoring system for an optical digital transmission system, said optical repeater monitoring system comprising:

• transmission stations having terminal transmitter means for transmitting control commands and a burst carrier;
• a pair of opposite direction lines between said transmission stations, said pair of opposite direction lines being a first line and a second line;
• a plurality of repeaters inserted in said lines, each of said repeaters having at least a pair of regenerators, each of said regenerators having a pair of monitoring circuits, said monitoring circuits includes,
• a flip-flop means for dividing frequency of signals in said first line to derive said control commands and said burst carrier,
• a command control reception means for receiving and for detecting said control commands and said burst carriers in said first line from said flip-flop means,
• a counter means for detecting parity errors in said second line and for counting parity errors,
• a timing generation means for reading said counter means when said control command reception means detects said burst carrier in said first line, and
• a phase modulator means for performing phase modulation to a clock pulse derived from said second line according to a binary code in said counter means,
• wherein said control commands and said burst carrier being constituted by arranging parity bits of in-service data in said first line, said control commands including first, second and third control commands, said first control command for controlling said plurality of repeaters to start said error counting in said second line and to store the number of errors in said counter means, said second control command for controlling said plurality of repeaters to stop said error counting in said second line, said third control command for designating a particular regenerator to return errors to said transmission station, and said burst carrier for sending errors from said counter means to said transmission station, said errors being sent by phase modulation of clock pulses for in-service data in said second line.