This Unsigned32 value (1 to 2,590,845, default 1) sets the number of block errors a given one-second interval must exceed for that second to count toward Signal Degrade (SD) detection on an OTU2 (10.7 Gb/s optical transport unit) line trunk. An administrator raises or lowers this threshold to match the expected background error rate of the link, since a link with naturally higher noise would need a higher threshold to avoid nuisance degrade alarms. For example, an administrator troubleshooting a marginal optical path on OTU2 might raise this threshold above the default of 1 so only intervals with clearly abnormal error counts count against the degrade-interval counter.