| 摘要 |
A signal transmission system uses an optical signal for carrying traffic information, and is also brightness modulated by a relatively low frequency signal. It is impractical to monitor directly the traffic information on the optical carrier for the presence of errors, and the error rate in the low frequency modulation is monitored, as its error rate is found to be indicative of traffic error. The system uses a number of traffic-carrying optical carriers, and also a supervisory or overhead optical carrier, all of which are provided with low frequency modulations whose error rates can be monitored to provide an indication of system performance. <IMAGE> |
