nbsCoherentStatsMinOSNR is read-only and holds the minimum optical signal-to-noise ratio (OSNR) observed on this coherent optical interface since statistics collection last started or was cleared (nbsCoherentStatsState), i.e. how strong the optical signal is relative to the accumulated noise floor across the fiber path; not-supported is encoded as 0xFFFFFFFF. Unit measurement: 0.1 dB. A sysadmin treats it as a longer-run baseline for this specific optic/fiber path, useful for spotting a slow drift in link quality that a single quarterHour or twentyfourHour sample in nbsCohpmCurrentTable might not reveal.