This read-only CoriantTypesOpticalDB value reports the current Optical Signal-to-Noise Ratio measured on the coherent optical channel (och-os) on the line side of a pluggable transceiver, expressed in dB. An administrator treats this as one of the primary health metrics for a coherent optical channel, since a falling OSNR is often the earliest warning sign of an amplifier, span-loss, or filtering problem well before the channel actually loses service. For example, watching OSNR trend downward over time on och-os would prompt an administrator to inspect upstream optical amplifiers or check for added loss in the path before the channel degrades far enough to actually fail.