| 摘要 |
PROBLEM TO BE SOLVED: To equalize the wavelength of an optical signal for monitor in a redundant constitution standby system to that of a main signal and to reduce the scale of an equipment. SOLUTION: On the standby state, station-side optical circuit terminating devices (OLT) 21 and 22 attenuate optical outputs of optical transmission circuits 201 and 202 by optical attenuation circuit 101 and 102 and output them. A standby system monitor circuit (MON) 9 of a subscriber line optical terminating device (ONU) 1 sets an optical level discrimination threshold to a value lower than the optical level discrimination threshold of an optical reception circuit (RCV) 8 to discriminate whether these is an optical reception signal or not. By the standby system monitor circuit 9, the normal state of the standby system (OLT) is confirmed if a discrimination output signal is detected as all '1'. If the optical output of the standby system is broken, a current system main signal is detected as a signal changed to '0' and '1' to recognize the abnormal state of the standby system. |
