Patent ID: 8171354

Claim:
A communication system in which a transmitter and a receiver are connected through an optical transmission line, wherein the transmitter and the receiver communicate with each other through a plurality of communication channels, wherein the transmitter comprises: a first memory for storing first data and second data; a first modulator for modulating an optical signal according to the first and second data; a first communication section for transmitting a modulated optical signal to the receiver through a first communication channel; a first transceiver for data communication with the receiver through a second communication channel; and a first controller controlling operation timing of the first modulator, the receiver comprises: a second memory for storing third data; a second communication section for receiving an optical signal from the transmitter through the first communication channel; and a second modulator for modulating a received optical signal according to the third data; a photo detector for detecting fourth data based on the received optical signal and an optical output signal of the second modulator; a third memory for storing the fourth data; a second transceiver for data communication with the transmitter through the second communication channel; and a second controller controlling operation timing of the second modulator and the photo detector, wherein at least one of the transmitter and the receiver further comprises a third controller which performs: measurement for at least one monitored item based on the first to fourth data; comparing a measured value for each monitored item with at least one fault-detection threshold for the monitored item, to determine occurrence of a corresponding fault when the measured value exceeds the fault-detection threshold; and when it is determined that the corresponding fault occurs, performing recovery of the communication system from the corresponding fault.