The recommended order for the troubleshooting steps is B, as follows:

Retrieve the channel power trace.This step is useful to identify the affected channel and its power level, as well as to check if there are any fluctuations or anomalies in the power trace that could indicate a channel absent issue1.

Retrieve the cross-connection (XC) details and see what Wave Keys should be present.This step is necessary to verify which Wave Keys are expected to be present on the node, card, and port based on the XC configuration2.Wave Keys are unique identifiers for wavelength tracking that are encoded by Optical Transponders (OTs) into each service wavelength direction3.

Go to the suspected troubled node / card / port and look at Wave Keys (in / out). This step is helpful to compare the observed Wave Keys with the expected Wave Keys, and to locate the source of the problem.If a Wave Key is missing or mismatched, it means that there is a channel absent issue on that node, card, or port4.

Check observed Wave Keys against expected Wave Keys. This step is the final solution to resolve the issue and restore the normal operation of the node. The observed Wave Keys should match the expected Wave Keys based on the XC configuration.If not, the XC configuration should be corrected or the faulty node, card, or port should be replaced5.Reference:Nokia Optical Diagnostics and Troubleshooting Course | Nokia,Optical User Guide - Nokia,Alcatel-Lucent 1830 PSS-8 and PSS-16 Photonic Service Switch