This is the master enable/disable switch for whether this port's ATM threshold-crossing-alert (TCA) monitoring, covering all the HEC, buffer overflow, framer FIFO, and lookup failure alerts described above, is active at all. Disabling this on a specific port turns off every one of that port's individually configured TCA alert periods and thresholds at once, so an admin troubleshooting why a port is not raising any TCAs despite obvious congestion should check this master switch before assuming the individual thresholds are simply set too high. A newly installed port with all its TCA thresholds carefully tuned would still raise no alerts at all if pportATMTcaEnable itself was left disabled on that port.