Comprehensive and Detailed Explanation From Nokia Optical Networking Fundamentals:

In a CDC-F (Colorless, Directionless, Contentionless, Flex-grid) architecture, the placement of monitoring points is vital for end-to-end visibility of wavelengths. Nokia's Wavelength Tracker technology relies on these points to detect the unique 'keys' or signatures associated with each wavelength. In a CDC-F node, the primary monitoring points are located on the IRDMxx (Intelligent Reconfigurable Demultiplexer/Mux) line interfaces and the CWR (Colorless Wavelength Router) CLS (Colorless) interfaces.

The IRDM monitoring points allow the system to verify the power and presence of wavelengths as they enter or leave the fiber spans (degrees). The CWR CLS monitoring points are critical because they provide visibility at the 'Colorless' add/drop stage. By having monitoring at both locations, the WaveSuite Network Operations Center (WS-NOC) can pinpoint exactly where a signal loss or power degradation is occurring---whether it's in the external fiber plant or within the internal colorless switching fabric of the ROADM. This granular visibility is what allows Nokia's 'Power Management' to automate balancing across complex mesh topologies.