On Packet Dropping Schemes of Active Queue Management Mechanism for Realizing Robustness against Network Status Changes

Recently, several router-based congestion control mechanisms have been proposed to support an end-to-end congestion control mechanism of TCP (Transmission Control Protocol). In this paper, we focus on a RED (Random Early Detection) router, which is one of promising router-based congestion control mechanisms. The RED router randomly drops the arriving packet by alignment probability to an average queue length (the number of packets at the buffer). However, no examination has been performed whether the line type function of the packet dropping probability is good or not. In this paper, we make it clear what function, which determines the packet dropping probability, is suitable from the viewpoint of the steady state performance and the transient behavior of the RED router using the mathematical analysis. Throughout some numerical examples, it is shown clearly how the performance of the RED router changes when the function, which determines the packet dropping probability, is a line type, a concave type and a convex type. Consequently, if the function, which determines the packet dropping probability, is made into a concave type, compared with the case where the function is a line type, it is shown that the transient behavior of the RED router and the robustness against the network status changes can be improved although the average queue length of the RED router in the steady state becomes large.