| 摘要 |
The invention finds particular application in an optical communication system including a transmitting terminal, a receiving terminal and an intermediate relay station. The system may be set to operate in a normal mode or in a standby mode. A transmission terminal determines whether a signal is present at its external input using Loss of Signal (LOS) detection unit 14. If there is no signal and the system is in a standby mode then the transmitter will output a "test" signal. The relay station and the receiving terminal will therefore not realise that there has been loss of signal, and will consequently be prevented from issuing alarm signals. If however the system is in a normal mode the transmitter will output the signal received at its external input, so that if there is signal loss the relay station and the receiving terminal will produce alarm signals. Maintenance personnel may initiate the standby mode, but the system preferably reverts to normal mode once the external input has been observed to be in a connected state for a period of time in excess of a predetermined threshold. |
