This Counter32, in the bpCosStatsTable indexed by stack unit, port pipe, BP port, and COS queue number, reports the packet buffer currently used by a specific class-of-service queue on that backplane port. Admins drill into this per-queue table when a port-level buffer alert needs to be traced to a specific COS/priority queue, given Trident2 supports 10 unicast and 5 multicast queues per port. A queue whose usage is disproportionately high relative to its siblings points to that traffic class as the congestion source.