This read-write integer (0-100 percent) sets the tail-drop threshold, the queue-fill level, at which Drop Precedence 0 packets in this tentative service class start being tail-dropped. Since DP0 typically marks the most-protected traffic, this threshold tells the admin how full the queue must get before even that traffic is discarded outright. For example, setting this to 90 means DP0-marked packets are only tail-dropped once the queue reaches 90% occupancy, protecting them until nearly the last moment.