Some observations on the dynamics of a congestion control algorithm

Abstract

We use simulation to make some observations about the behavior of the congestion control algorithm currently embedded in the 4.3-Tahoe BSD TCP implementation. We investigate a simple case of a few TCP connections, originating and terminating at the same pair of hosts, using a single bottleneck link. Our simulations reveal two unexpected phenomena. First, packets from the individual connections, rather than being mixed together, completely separate into individual clusters. Second, every connection loses a single packet during each congestion epoch. As a way of exploring the cause of these phenomena, we discuss how the behavior is altered by modifications to the congestion control algorithm and to the switch queue control algorithm.