Patent ID: 7489869

Claim:
A station-side communication device connected to a plurality of subscriber-side communication devices via an optical combining device; sending, to each of said plurality of subscriber-side communication devices, a distance measurement request signal for measuring the distances to each of said plurality of subscriber-side communication devices; computing transmission delay times of optical signals from each of said plurality of subscriber-side communication devices based on the reply received to said distance measurement request signals from each of said plurality of subscriber-side communication devices said station-side communication device comprising: a threshold control part for identifying the voltage level of said distance measurement signals converted from optical signals into electrical signals; a signal detection part for detecting breaks in said distance measurement signals; a transmission granting part for determining the timing at which transmission of optical signals is granted, with respect to each of said plurality subscriber-side communication devices; and a reset timing generation part for resetting the voltage level of said distance measurement signal in said threshold control part if a break is detected in said distance measurement signals.