To provide a subscriber-side optical transmission line terminator unit (ONU) in a passive optical network (PON) system with a IP telephone service, capable of performing low power consumption operation.
A station-side optical transmission line terminator (OLT) and the ONU monitor communications on a PON system so as to shift the ONU in non-communication state to sleep state. The OLT holds a MAC address of a SIP call termination terminal connected to the ONU so as to monitor an incoming call of the SIP call termination terminal. When the SIP call termination terminal receives the incoming call, the OLT determines whether or not optical transmission/reception of the ONU existing on a communication channel is restored within response time limit, and if the ONU is not restored timely, the OLT responses to the incoming call alternatively.
KAZAWA TORU
OTANI ATSUSHI
Yuji Toda