This is the highest value recorded during the current performance-monitoring interval of the polarization-dependent loss (PDL) measured on this channel during the current performance-monitoring interval, expressed in dB, reflecting how much the signal's loss varies depending on its polarization state as it passes through the optical path. The highest PDL seen in the interval matters most, since excessive PDL directly erodes OSNR margin and can push a channel toward failure even when total received power looks otherwise normal. For example, if polarizationDependentLossMax on a channel climbs steadily over several months even though OSNR looks stable, an admin would suspect an aging optical component like a wavelength selective switch rather than a fiber issue.