This read-only Unsigned32 holds the high-order 32 bits of the 64-bit threshold value that was crossed to trigger this event, per its description, paired with cienaCesOamEventLogThresholdLo. As with the window's high-order field, this will be zero in essentially all realistic deployments since configured thresholds, like '10 errored frames', fit comfortably in 32 bits, and the field exists only to satisfy the standard's 64-bit representation. An engineer auditing threshold-crossing events would generally find ThresholdHi uninteresting and focus on ThresholdLo, only checking this field if an unusually large threshold value were ever configured.