| 摘要 |
PURPOSE:To demarcate a fault position by investigating history information without resetting a loop-back mode even after the recovery from the fault while an annular dual communication system consisting of a main trunk line and a subordinate trunk line is faulty and loop-back operation is carried out. CONSTITUTION:For example, the main trunk line 1 has a fault between nodes 3A and 3B and is placed in loop-back operation through loop-back circuits 4B and 5A. In this case, a loop-back fixation flag 19 is set to '1', a photodetection history flag 14 is initialized to '0', and the loop-back operation is inhibited from being reset. When light is outputted from an E/O converter 8 to the subordinate trunk line 2, it reaches an O/E converter 9A to detect the normalcy of the light level, and a photodetection flag 14 is set to '1'. Here, the loop-back fixation flag 19 is reset and then an information request frame is sent out; and the photodetection history flag 14 is checked, thereby knowing that the subordinate trunk line 2 is normal and the main trunk line 1 is defective when the flag 14 indicates '1'. Consequently, the fault is demarcated over a data communication. |
