This Counter64 tallies ATM cells received at ingress and passed onto the circuit with the Cell Loss Priority bit set to 1, marking them as lower priority and the first to be dropped if the network becomes congested -- the ATM-cell-level equivalent of the DE bit used in Frame Relay. A high count here relative to circuitInCLP0Cells indicates this circuit is carrying a substantial amount of best-effort or excess traffic that the network is prepared to discard first under load. For example, bulk data transfer traffic sharing an ATM circuit with voice traffic would typically be marked CLP1 so it's sacrificed before the voice cells during any congestion event.