Congestion Control and Periodic Behavior Anna

used by TCP and other transport protocols — causes the transmission rate of a long-lived flow to oscillate. This paper is about the tendency of multiplexed flows on a bottleneck link to oscillate causing " aggregate periodic behavior ". As a consequence, bottleneck links can become underutilized, wasting capacity. One simple way to prevent this is to use larger buffers in the bottleneck router. We explore how large these buffers need to be to absorb oscillations. Another proposed solution is to use a randomized active queue management algorithm, such as RED. A goal of RED is to reduce " global synchronization " of TCP flows, and hence avoid oscillations. Our results suggest that RED does not reduce aggregate periodic behavior when compared to Drop Tail. Perhaps surprisingly, our results and a simple analytical model suggest that the tendency for aggregate traffic to oscillate is robust against many forms of disturbances added to the timing of feedback and reaction, even if each constituent flow shows little or no sign of periodicity. Different flows can be in different states and yet conspire to make their sum have periodic behavior.