Patent ID: 8687960

Claim:
A communication method of an optical communication system in which a plurality of user-side optical-line terminals (ONUs) are connected to a station-side optical-line terminal (OLT) by using a common optical fiber, comprising the following steps (a) to (c): (a) allocating, by the OLT, a transmission bandwidth to an ONU, the ONU capable of an operation in a sleep mode in which an optical transmitter of the ONU is tentatively halted for a predetermined sleep period, and transmitting a transmission bandwidth notification to the ONU when the ONU is in the sleep mode and when the ONU is not in the sleep mode; (b) receiving, from the ONU to which the transmission bandwidth is allocated, a response signal when the ONU is not in the sleep mode, wherein the response signal is or is not received during the sleep mode; and (c) suppressing, by the OLT, an alarm in the sleep mode of the ONU, the alarm being caused by a communication failure with the ONU on a basis of the response signal not being received from the ONU.