Making Router Buffers Much Smaller The following three papers are invited editorials on the topic of Buffer Sizing. Currently, router manufacturers typically use a rule of thumb to choose buffer sizes: this rule says to provide at least one round trip time's worth of buffering. These three papers reflect a feeling in some parts of the research community that this rule of thumb is out of date and needs to be revisited. Part I: Buffer Sizes for Core Routers (D. Wischik and N. McKeown) introduces the problem. It presents some simple models which suggest that, in routers with a high degree of statistical multiplexing, buffers can be much much smaller than the rule of thumb suggests. A key part of the analysis is synchronization. Broadly speaking, if TCP flows are synchronized then large buffers are needed; if TCP flows are unsynchronized then small buffers are sufficient. Part II: Control Theory for Buffer Sizing (G. Raina, D. Towsley, D. Wischik) outlines a control-theoretic analysis of synchronization. This analysis indicates that small buffers actually induce desynchronization. It also suggests how TCP and/or active queue management schemes might be redesigned to be less prone to synchronization. Part III: Routers with Very Small Buffers (M. Enachescu, Y. Ganjali, A. Goel, N. McKeown, T. Roughgarden) shows why very small buffers are sufficient, so long as we are willing to sacrifice a small amount of throughput. The analysis shows that if the packets belonging to a TCP flow are sufficiently spaced out, then 10 “20 packet buffers are enough, independent of the link speed. Packets are spaced naturally when flows enter through access links that are much slower than the backbone links. Alternatively, packets can be spaced out by making a small modification to TCP, described elsewhere as TCP Pacing. The models described in these three papers are supported by mathematical theory and by simulation, but so far there has not been any systematic experimental investigation. In parallel, we are starting to work with network operators to conduct experiments, and will report our results separately. And we hope that these papers will encourage more network operators to experiment with small buffers. We also hope to attract the attention of researchers who work on all-optical routers. With current optical technology it is simply infeasible to size buffers according to the rule of thumb ” but it is feasible to size them to hold 10 “20 packets. This work, then, opens the door to all-optical packet-switched core networks. Prof. N. McKeown Computer Science, Stanford University nickm@stanford.edu Dr. D. Wischik Computer Science, UCL D.Wischik@cs.ucl.ac.uk acm sigcomm ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ACM SIGCOMM Computer Communication Review Volume 35, Number 2, July 2005

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