This read-only integer reports the last known Optical Signal-to-Noise Ratio (OSNR), in permil (tenths of a percent), for a specific detected DWDM channel. Admins monitor this to assess the signal quality of a wavelength, since a low OSNR predicts a rising bit error rate even if raw power looks acceptable. For example, a channel showing a declining OSNR trend, even with stable power readings, would warn the admin of accumulating noise or dispersion issues on that wavelength's path.