Passive optical network system

A communication device connected to optical network units through optical fibers, comprising:

• a function of measuring communication distances to the optical network units and holding measurement results;
• and a function of adjusting a light intensity of a downstream communication signal to the optical network units on the basis of the measurement results, and notifying the optical network units of a transmission schedule of the downstream communication signal in a given period prior to transmission of the downstream communication signal, and
• a function of transmitting a signal having arrival timing information in a given period, about the light intensity of the downstream communication signal addressed to the respective optical network units, to the respective optical network units in advance, prior to processing of transmitting the downstream communication signal to the respective optical network units, and
• a function of setting a given value as a transmission period of the transmission schedule for each of the optical network units or an optical network unit group.

An optical network unit connected to an optical line terminal through an optical fiber, comprising:

• a reception timing determination unit that acquires, upon receiving an optical signal transmitted from the optical line terminal, from the received signal, timing information on which an optical signal addressed to the subject optical network unit, or an optical signal having a light intensity that can be received by the subject optical network unit arrives at the subject optical network unit, with reference to the received signal;
• a block mechanism that blocks the optical signal when the optical signal transmitted from the optical line terminal exceeds a light intensity receivable by the optical network unit;
• a discard function that discards the optical signal when the optical signal transmitted from the optical line terminal falls below a light intensity receivable by the optical network unit;
• and
• a function of acquiring the optical signal of the light intensity that can be received by the subject optical network unit, or an arrival timing of the optical signal addressed to the subject optical network unit in a given period, prior to reception of the optical signal.