Patent ID: 7512341

Claim:
A station-side communication device connected to a plurality of subscriber-side communication devices via an optical combining device; sending, to said plurality of subscriber-side communication devices, a distance measurement request signal for measuring the distances to respective ones of said subscriber-side communication devices; computing transmission delay times of optical signals from individual ones of said subscriber-side communication devices by receiving distance measurement signals which are replies from said plurality of subscriber-side communication devices with respect to said distance measurement request signal, and comprising: a threshold control part identifying the voltage level of said distance measurement signals converted from optical signals into electrical signals; a signal detection part detecting breaks in said distance measurement signals from said threshold control part; a transmission granting part determining the timing at which transmission of optical signals is granted, with respect to an individual subscriber-side communication device; a reset timing generation part that, while it is being notified from said transmission granting part that distance measurement is carried out to and from said subscriber-side communication devices, sends a plurality of reset signals, indicating that said voltage level is reset, to said threshold control part; and a serial number mask generation part designating at least a part of the serial number allocated dedicatedly in said subscriber-side communication device, said serial number mask generation part limiting, by notifying said plurality of subscriber-side communication devices of the serial numbers designated by said serial number mask generation part, said subscriber-side communication devices transmitting said distance measurement signals to said subscriber-side communication devices that include said designated serial numbers.