This counts received cells on this port that were discarded due to errors detected at the ATM layer itself, since the last reset, distinct from the physical-layer HCS/BIP errors. An ATM-layer error on this specific port typically means the cell's header passed physical-layer checks but violated something at the ATM protocol level, such as an invalid VPI/VCI combination or a reserved header pattern, so this counter is where you would look when physical-layer stats are clean but cells are still being lost. A port with zero HCS/BIP errors but a climbing pportAtmLayerErroredReceivedCells count would point toward an ATM-layer protocol violation from the sending equipment, not a physical transmission fault.