OPTICAL NETWORK UNIT, OPTICAL LINE TERMINAL, CONTROLLER, COMMUNICATION DEVICE, OPTICAL TRANSMISSION SYSTEM AND POWER SAVING CONTROL METHOD

PROBLEM TO BE SOLVED: To provide an ONU that can quickly cancel a power saving state when downlink traffic occurs in the case where an optical receiving side is in the power saving state.SOLUTION: ONUs 1-1 to 1-n constituting a PON system together with an OLT 2 each comprise: an optical receiver 17 for performing reception processing of an optical signal received from the OLT 2; an optical transmitter 18 for performing transmission processing of an optical signal to be transmitted to the OLT 2; a PON control unit 13 for controlling transition to a power saving state of the optical receiver 17 and optical transmitter 18; and an L2SW 12 for detecting reception of alternative data which is data transmitted by the OLT 2 via an alternative network which is a communication network different from the PON system. The PON control unit 13 cancels the power saving state of the optical receiver 17 when it detects reception of the alternative data if the optical receiver 17 is in the power saving state.