This counter tracks the number of received bytes dropped for this specific egress CoS queue (cienaCesPmQueueGroupQueueIndex), as stated in the MIB description. A count that climbs here specifically (rather than on cienaCesPmBasicRxTotalStats) means the loss is happening at the per-queue scheduling/shaping stage -- this queue's assigned bandwidth or buffer depth is too small for the class of service mapped to it -- not at the physical ingress, so the fix is to re-tune that queue's CIR/weight or buffer allocation rather than to look at the port's overall rate. For example, 3,173 bytes dropped from this one queue index in a single 24-hour bin, while sibling queue indexes on the same port show near-zero drops, would point straight at that one CoS class being under-provisioned rather than a link-wide capacity problem.