This sets the count threshold of egress lookup failure events that, within the corresponding alert period, triggers a threshold-crossing alert on this port. Because a lookup failure means a cell arriving at this port for egress had no valid forwarding entry, a rising count against this threshold on this specific port is a strong indicator of a stale VC table entry or a race between circuit teardown and still-arriving traffic, rather than a physical-layer or QoS congestion issue. A spike in egress lookup failures on this port crossing this threshold right after a batch of PVCs were reprovisioned would point to a timing gap in updating this port's forwarding table during that change.