COMMUNICATION SYSTEM, STATION SIDE COMMUNICATION DEVICE, USER SIDE COMMUNICATION DEVICE, COMMUNICATION METHOD, AND CONTROL DEVICE

An OLT 1 includes an OLT control unit 2 that generates a control signal for controlling a power saving operation of an ONU 10-1 by specifying a different idle period with respect to a first power saving operation in which an optical receiver 142 is operated while an optical transmitter 141 of the ONU 10-1 is controlled to a power saving state and a second power saving operation for controlling the optical transmitter 141 and the optical receiver 142 to the power saving state, and a station-side transmitter that transmits the control signal generated by the OLT control unit 2 to the ONU. The ONU 10-1 includes an ONU control unit 11 that receives the control signal via the optical receiver 142 to selectively perform the first power saving operation and the second power saving operation based on the idle period specified by the control signal.