Patent ID: 7711268

Claim:
A passive optical network system comprising: a station-side communication device; a plurality of subscriber-side communication devices; an optical splitter and a plurality of optical fibers connecting the plurality of subscriber-side communication devices to the station-side communication device, wherein the station-side communication device determines timing of transmitting a signal to the station-side communication device from the subscriber-side communication devices for communications between the station-side communication device and the subscriber-side communication devices, the station-side communication device comprising: a threshold control part detecting a voltage level of a received signal converted into an electrical signal from an optical signal transmitted from one of the plurality of subscriber-side communication devices; a signal detection part detecting breaks in the received signal; a transmission granting part determining the timing at which transmission of optical signal from each of the subscriber-side communication devices is granted; and a reset timing generation part generating a reset signal for resetting the voltage level detected by the threshold control part when it is notified from the signal detection part that there has been detected a break in the received signal, wherein: a distance measurement request signal for measuring distances between said respective plural subscriber-side communication devices and the station-side communication device is transmitted to the plurality of subscriber-side communication devices, and response signals from the plurality of subscriber-side communication devices in response to the distance measurement request signal are received to calculate transmission delay times of optical signals from the subscriber-side communication devices; and while the transmission granting part is notifying the subscriber-side communication devices that distance measurement is carried out, when the signal detection part detects a break in a received response signal from one of the subscriber-side communication devices, the reset timing generation part sends a reset signal to the threshold control part, and then the threshold control part executes reception of a response signal from another subscriber-side communication device.