Pete Heist’s Thoughts on ECN

Although I feel the usual pull of team Grey, I think I’ll call myself a Purple for this, possibly overly simplistic reason:

In theory, the ECN bits only give congestion control algorithms more information than they would otherwise have, and in a perfect world, dropping packets would be a measure of last resort.

Purple should lose if it can be shown that nothing can (practically) be done to come up with an agreed upon treatment of ECN bits that results in “better” congestion control with less packet loss, most of the time. Or if there are commonly observed, demonstrably harmful pathologies that are not reasonably possible to overcome.

Presently, I’m more interested in what happens to traffic for regular people and small to medium sized ISPs, say 5-200ms RTTs and 1-100Mbit bitrates, than what happens in the data centers of trillion dollar companies.

Lastly, my interest in ECN is to understand better what tools and metrics can be used on real-world traffic to evaluate its impacts. If I can contribute anything to this project, I hope it will be to bring some unsettled contradictions to slightly earlier resolutions…