This sets the absolute maximum length of the UBR/ABR queue, beyond which the card discards all cells regardless of CLP marking, the ABR/UBR counterpart to cardClp01CbrThreshold. As the absolute ceiling for the lowest-priority queue class on the card, reaching this threshold represents genuine exhaustion of even the most congestion-tolerant traffic's buffer space, which, given ABR/UBR's rate-adaptive and best-effort nature, an admin would treat as a sign of sustained oversubscription on that queue rather than a brief burst. For example, sustained discards at cardClp01UAbrThreshold on the ABR/UBR queue, unlike an isolated brief hit, point to genuine bandwidth oversubscription for best-effort traffic on that card rather than normal burst absorption.