This sets the queue-depth threshold at which the NRTS processor begins discarding cells specifically on multicast circuits. Because multicast traffic can fan out to many destinations from a single source, tuning this threshold controls how aggressively the card protects itself from a single misbehaving or oversubscribed multicast source overwhelming shared buffer resources before it starts shedding that source's cells. For example, lowering cardNrtsMcastDiscardThresh protects the card's shared buffers from being monopolized by one high-volume multicast feed, at the cost of dropping that feed's cells sooner under load.