This counts cells queued for transmission on this port that were discarded because the ATM-IWU was congested, since the last reset. As the outbound counterpart to pportCongestedReceivedCells, a rising value here on this specific port means the egress side of the interworking unit cannot keep up with the cell rate being handed to it for transmission, which is a different bottleneck than pportOutDiscardsCell's simple buffer-overflow congestion. If this counter rises sharply right after adding a new high-bandwidth PVC through this port, the ATM-IWU's transmit processing capacity, not just its buffers, may be the limiting factor.