This is a configurable per-minute threshold that tells the card how many BTUs carrying an invalid PVC identifier it must see before it fires an SNMP trap, with zero disabling the check. Because PVC IDs get invalidated when a permanent virtual circuit is deleted or misconfigured on one end but cells for it keep arriving, tuning this threshold controls how sensitive this specific card is to stale or misconfigured PVC traffic without flooding you with traps for a handful of stray cells. An admin decommissioning a PVC might set this to 50 so that only a sustained stream of orphaned cells, not a brief burst during teardown, triggers an alert.