Yashar Ganjali, PhD Candidate
High Performance Networking Group, Stanford University
http://www.stanford.edu/~yganjali

hosted by John Wroclawski

Wednesday, October 26, 2005
1:30PM PDT
11th Floor Conference Room (1137)

Routers with Small Buffers
Joint work with: Guido Appenzeller, Mihaela Enachescu, Ashish Goel, Tim Roughgarden, Nick McKeown

Internet routers require buffers to hold packets during times of congestion. The buffers need to be fast, and so ideally they should be small enough to use fast memory technologies such as SRAM or all-optical buffering. Unfortunately, a widely used rule-of-thumb says we need a bandwidth-delay product of buffering at each router so as not to lose link utilization. This can be prohibitively large. In a recent paper, Appenzeller et al. challenged this rule-of-thumb and showed that for a backbone network, the buffer size can be divided by \sqrt(N) without sacrificing throughput, where N is the number of flows sharing the bottleneck. In this work, we explore how buffers in the backbone can be significantly reduced even more, to as little as a few dozen packets, if we are willing to sacrifice a small amount of link capacity. We argue that if TCP sources are not overly bursty, then fewer than twenty packet buffers are sufficient for high throughput. Specifically, we argue that O(\log W) buffers are sufficient, where W is the maximum window size of each flow. We support our claim with analysis and a variety of simulations. The change we need to make to TCP is minimal---each sender just needs to pace packet injections from its window. Moreover, there is some evidence that such small buffers are sufficient even if we don't modify the TCP sources so long as the access network is much slower than the backbone, which is true today and likely to remain true in the future.

We conclude that buffers can be made small enough for all-optical routers with small integrated optical buffers.

Bio:

Yashar Ganjali is with High Performance Networking Group at Stanford University, where he is working toward his PhD degree. He has got a BSc in Computer Engineering from Sharif University of Technology, Tehran, Iran in 1999, and a MSc in Computer Science from University of Waterloo, Waterloo, Canada in 2001. He is currently involved with the buffer sizing project; the goal is finding out the impact of reducing the buffer size in core routers from millions of packets to just tens of packets, and thus exploring the possibility of building all-optical networks. His other research interests include analysis and design of high performance switches, scheduling algorithms, congestion control, routing protocols, and network optimization.