Labeling of signals in transparent optical networks

Management, switching and protection of signals in a core network depends on transmission of management data associated with specific channels, e.g. for identification of channel origin, destination and content. SDH and DWDM networks provide dedicated data channels for this purpose. While reliable and standardized for SDH/SONET networks, such solutions are expensive and not compatible with an "all-optical network" approach. Some general remarks are made about optical signal labels and some known applications for them are listed. Labeling techniques proposed for transparent networks are reviewed, with special attention given to: pilot tones; low-frequency and high-frequency subcarrier modulated data channels; insertion of label data into fixed locations within the frame of the host signal. Although there are several options for labeling and attaching extra information to signals in transparent optical networks, standards are lacking and demand for high performance all-optical networks has not arrived yet.