The impact of the average packet arrival rate on the drop/mark probability of the Fast Congestion Notification (FN) mechanism

The performance of TCP-based applications depends on the selection of queue management mechanism in network routers and how well its control decisions are made. Fast Congestion Notification (FN) mechanism enables the two control decisions, packet admissions and congestion control directing, to be made together. This permits sending congestion avoidance notification as early as required, even if the queue is almost empty, and preventing congestion notification even if the queue is almost full but the arrival rate is manageable. This leads to good buffer utilization and proper congestion detection. This paper describes the linear packet dropping/marking probability of the Fast Congestion Notification (FN) and examines its properties as a function of the average arrival rate for fixed values of allowed/desired change in queue level. The paper also studies how changes in the queue affect the dropping/marking probability function shape. The paper shows that the larger the drain (growth) in the queue, the smaller (larger) is the largest average arrival rate that can be endured before activating the packet drop/mark mechanism, and the larger (smaller) the maximum achievable drop probability.