WDM optical network and switching node with pilot tone communications

A fiber optic wavelength division multiplexed ring comprising:

• a plurality of switching nodes,
• means for generating a plurality of wavelengths organized into bands on said ring, and transmitting a like plurality of traffic channels associated with said wavelengths;
• and
• means for transmitting maintenance channel data on at least one of said wavelengths as a pilot tone;
• wherein said maintenance channel has a modulation depth, such that the system can determine the performance of the respective traffic channel by monitoring the bit error rate (BER) or waterfall curve performance of the maintenance channel data and without looking at the maintenance data.

A fiber optic wavelength division multiplexed ring comprising:

• a plurality of switching nodes,
• means for generating a plurality of wavelengths organized into bands on said ring, and transmitting a like plurality of traffic channels associated with said wavelengths;
• and
• means for transmitting maintenance channel data on at least one of said wavelengths as a pilot tone;
• wherein said maintenance channel has a known modulation depth with respect to said respective traffic channel, such that the system can determine the performance of the respective traffic channel by monitoring the bit error rate (BER) or waterfall curve performance of the maintenance channel data and without looking at the maintenance data.