Patent ID: 6944399

Claim:
A method for controlling substitute signal transmission in a wavelength division multiplexed (WDM) device having a plurality of sub-bands, each sub-band including at least two signal channels which carry respective data signals, and a plurality of substitute signal transmitters, each substitute signal transmitter generating a substitute signal and corresponding to a respective one of the plurality of sub-bands, comprising: identifying signal channels having a predetermined characteristic within each of the plurality of sub-bands; turning on a substitute signal transmitter if the sub-band corresponding to the substitute transmitter includes a predetermined number of signal channels having said predetermined characteristic; combining the data signals and the substitute signals into a WDM signal; transmitting the WDM signal over an optical transmission fiber; detecting a fault in a substitute signal transmitter based on detected wavelengths and power levels of the substitute signals; and turning on a backup transmitter corresponding to the substitute signal transmitter in which the fault is detected.