This counts ATM cells that were dropped specifically due to congestion, buffer or queue exhaustion, on this card, as opposed to header or VPI/VCI errors. Because this isolates congestion-caused drops from error-caused drops, a rising count here during peak traffic hours rather than randomly is the specific signature of the card's egress capacity being oversubscribed relative to demand, which is a capacity-planning trigger rather than a hardware-fault one. For example, cardOutDiscardCells spiking predictably every day during the same peak business hours points to genuine bandwidth oversubscription on that card rather than an intermittent hardware issue.