This field records how much the counter for FCoE frames that arrived on the wire but were discarded before being handed up to the Fibre Channel stack changed during the specific collection interval this historical record captured — a frozen snapshot of that one interval's increase, not a live running total. For a network admin, a nonzero value here on an otherwise healthy Ethernet link points specifically at FCoE buffer exhaustion or a lossless-Ethernet/priority-flow-control misconfiguration, not a generic Ethernet problem. For example, 0 frames in the last interval on this specific FCoE path would already be worth a closer look, since this counter should normally sit at or near zero.