Passive optical network system, optical line terminal, and optical network unit

A passive optical network system comprising:

• an optical line terminal;
• and
• a plurality of optical network units connected to the optical line terminal, wherein at least one of the optical network units comprises:
• a detecting unit configured to detect a decrease in a supply power to the optical network unit and inform the optical line terminal of the decrease in the supply power when the detecting unit detects the decrease,
• a transmission control unit configured to make a change in a transmission rate between the optical network unit and the optical line terminal on the basis of an instruction from the optical line terminal,
• wherein the optical line terminal comprises:
• a storing unit configured to store a transmission rate control information for specifying an upper limit of the communication bandwidth of each of the optical network units in a normal status, a power failure status, and a power saving status;
• and
• a time-division-multiplexing control unit configured to instruct each of the optical network units about an upstream transmission timing and an upstream transmission rate of transmitting the data toward the optical line terminal, and wherein, when the decrease in the supply power is informed by the optical network unit, the time-division-multiplexing control unit determines transmission clock rates providing communication bandwidths required in the normal status, the power failure status, and the power saving status and a transmission order of the data from each of the optical network units with reference to the transmission rate control information, and transmits a notice message to each of the optical network units to instruct an upstream transmission timing after the change in the transmission rate and an upstream transmission clock rate after the change in the transmission rate.