This counts received ATM cells on this port that were discarded specifically because the ATM-IWU (interworking unit) hardware was congested, since the last reset. Because the description ties this explicitly to IWU congestion rather than line errors, a rising count here on this specific port points to the card's internal processing or buffering being overwhelmed by inbound cell rate, not a physical signal problem. A port whose pportCongestedReceivedCells climbs during peak hours while its HCS and BIP counters stay flat would indicate the IWU hardware itself, not the line, is the bottleneck for that port at those times.