STATION SIDE OPTICAL NETWORK TERMINAL DEVICE, OPTICAL COMMUNICATION SYSTEM, ABNORMALITY DETECTION METHOD, AND DEVICE PROGRAM

PROBLEM TO BE SOLVED: To quickly and easily detect an abnormality in an Optical Network Terminal (ONU).SOLUTION: An Optical Line Terminal (OLT) comprises: scheduling means which assigns an exclusive transmitting timing to each ONU; control signal transmitting means which transmits to each ONU a control signal for making data transmitted along a transmitting timing assigned by the scheduling means; and monitoring means which monitors an optical signal received through a transmission path. In the scheduling means, scheduling is performed so that all the connected ONUs include a non-communication state where transmission of the optical signal is stopped. In the monitoring means, monitoring is performed including a reception state in the non-communication state.