REDUNDANT SYSTEM, STAND-BY SYSTEM TEST SYSTEM AND ITS METHOD

摘要

PROBLEM TO BE SOLVED: To provide a technology for detecting the abnormality of a light transmitting part and a light receiving part without allowing an optical signal transmitted from a stand-by system to collide with an optical signal transmitted/ received to/from a current system on an optical transmission line. SOLUTION: Each of the current system and the stand-by system has an optical switch for selecting whether an optical signal is to be transmitted to the optical transmission line or a returning line for returning the optical signal to its own station and an optical switch for selecting either one of the optical signal from the optical transmission line and the optical signal from the returning line.