PURPOSE: To quickly and exactly detect a communication abnormality in an optical communication system.
CONSTITUTION: A host communication controller 1 and slave communication controllers 2-1, 2-2,..., 2-n are connected by an optical fiber communication path 3. Communication information is transmitted in a bucket brigate system like the host 1 → the slave machine 2-1 → the slave machine 2-2 → the slave machine 2-3, for instance, and when communication information (solid line arrow) is outputted from each communication device, an echo back signal (dot line arrow) is also outputted. Therefore, because the echo back signal is not outputted from the slave machine 2-2 and the slave machines 2-1 and 2-3 which are adjacent to the slave machine 2-2 do not receive the echo back signal when an abnormality occurs in the slave machine 2-2, for instance, it is judged that the abnormality occurs in the slave machine 2-2.
SAIGO TOSHIAKI
YAMASHITA KATSUYA
OTSUKI FUMIO
NIPPON TELEGRAPH & TELEPHONE