Optical multiplex communication system, optical transmission apparatus, and control method of optical multiplex communication

An optical multiplex communication system comprising a transmission part and a receiving part;

• wherein optical signals having different wavelengths and respectively assigned to a plurality of channels are multiplexed so as to make multiplexed signals, and then amplified with an optical amplifier and transmitted to an optical transmission path, by the transmission part;
• the multiplexed optical signals are received through the optical transmission path and then amplified with another optical amplifier and de-multiplexed for respective channels so that a receiving process is implemented by the receiving part;
• the receiving part includes a transmission quality detecting part that measures and transmits transmission quality information for the channels based on a request from the transmission part;
• the transmission part includes a variable optical attenuation part controlling the optical signal level for the channels, an optical level setting part controlling the variable optical attenuation part based on a setting value, a setting control part adding the setting value to the optical level setting part based on a request for setting, and a setting protection part transmitting the request for setting to the setting control part;
• and
• the setting protection part sets a protection step number with respect to a state transition transmitting the request for setting so as to make the transmission quality information be in a target range of the transmission quality.