| 摘要 |
PROBLEM TO BE SOLVED: To realize high reliability of a communication network by making it possible to use a service through another communication path if abnormality occurs in communication on one communication path of duplicated communication paths.SOLUTION: A communication path is made duplex. The wavelength of signal light on one communication path of communication paths (7, 8) is converted into a different wavelength than that on the other path (54), the difference of optical path length of each communication path is measured by test pulse light (52), and based on its measurement result, optical path length is controlled such that the optical path lengths accord with each other (55, 53). Then, the optical power level difference of each communication path is measured by test pulse light (51b), and the optical power level of the second communication line 8 is attenuated and adjusted so that the optical power level difference will be in a permissible range. Thus, by always adjusting the optical path length within a range in which a link is not cut-off between communication devices 1, 2, even if abnormality occurs in communication on one communication path, the service will be available on the other communication path. |
