Abstract: In a point-to-multipoint network of an optical line terminal (OLT) and multiple optical network units (ONUS) wherein each ONU is enabled to send a signal only within a time period enabled for the ONU, the OLT (or a system installed therein) identifies a defective one of the ONUs. For each of a given series of time periods, the OLT measures an optical reception level of an optical fiber signal in the time period. The OLT stores, in advance, in a table at least the reception level of a received signal from each ONU in association with the ONU. The reception level is measured in a normal state where signals from the ONUs are exclusively received. For each of the given series of time periods, the OLT decides whether a signal from one of the ONUs associated with the time period is exclusively received with no collision with any other signal.

Abstract: In a point-to-multipoint network of an optical line terminal (OLT) and multiple optical network units (ONUS) wherein each ONU is enabled to send a signal only within a time period enabled for the ONU, the OLT (or a system installed therein) identifies a defective one of the ONUs. For each of a given series of time periods, the OLT measures an optical reception level of an optical fiber signal in the time period. The OLT stores, in advance, in a table at least the reception level of a received signal from each ONU in association with the ONU. The reception level is measured in a normal state where signals from the ONUs are exclusively received. For each of the given series of time periods, the OLT decides whether a signal from one of the ONUs associated with the time period is exclusively received with no collision with any other signal.

Abstract: A relay unit capable of avoiding the occurrence of simultaneous switching whatever data is received and thereby preventing malfunction of the device due to impulse noise, and a memory product having stored therein a computer program are provided. The relay unit includes a latch unit that temporarily stores converted parallel data; a determining unit that compares received data with subsequent data to be received subsequently and thereby determines whether to invert bits of data; and an inverting unit that invert bits of converted serial data. When the determining unit determines that bit-inverted parallel data is received as subsequent data, the determining unit transmits to the latch unit a signal instructing to prohibit from storing temporarily the received subsequent data and transmits to the inverting unit a signal instructing to invert bits of data.