| 摘要 |
In a first apparatus, transmission signals are inverted in a sending side and are restored in a receiving side in one direction of two-way communication, and transmission signals are not inverted in another direction, to thereby distinguish a signal reflected at a fault point of an optical fiber from normal receiving signals from the station of the other party. In a loopback test, an inverter provided in the receiving side of the former direction is bypassed and an inverter is inserted in the receiving side of the latter direction. In a second apparatus, overhead information for identifying stations is added in a sending side. In a receiving side, the overhead is extracted. The extracted overhead is compared with an identifier of the station of the other party in a normal operation and is compared with an identifier of the station itself in a loopback test. |
