Congestion Avoidance and Control

It makes sense to put this paper first, since it is good at framing the problems TCP was experiencing. The authors introduce a number of new algorithms for improving throughput and fairness; they are all classics now, including the RTT variance estimation and slow start. One of the design points the emphasize that has contributed to TCP's robustness is focusing on a wide spectrum of bandwidth-delay product regimes from slow packet-radio links to fast local wired networks. They develop a very simple variance estimator, implementable in just a few lines of c. The also outline the "slow start", which really starts exponentially fast. I actually find their diagram on page 4 pretty confusing; I think it's because they seem to be assuming that every packet will be acked; I don't think that's really the way TCP works though.

What's really interesting about this paper is its generality: any stream protocol will have to discover the available bandwidth and respond to latency changes due to causes beyond the endpoints' control. This leads to the maxim that "those who don't understand TCP are doomed to reinvent it," and based on my experience in sensor nets, we've imperfectly reinvented it at least several times. Although this is a bit of a digression, it's really interesting how TCP can take advantage of huge differences in buffering capacity (and thus window size) when devices with drastically different capabilities communicate.

The paper addresses a whole range of concerns, from the robustness of its estimators, to how easily they can be implemented with only integer arithmetic; I rather suspect that the SIGCOMM version didn't include some of the sample implementation. None the less, part of the beauty of this work is that they show you don't need complicated solutions to complicated problems, and to convince the community that although there were sophisticated ideas behind their fixes, there was no sophisticated implementation.