[e2e] TCP ex Machina

Keith Winstein keithw at mit.edu
Thu Sep 19 20:10:57 PDT 2013

Hello Detlef,

I appreciate your thoughts.

You wrote, "I'm not completely convinced that this approach actually yields
a congestion control algorithm which can be generalized and works with an
arbitrary scenario."

Of course, neither are we. As I wrote, this is academic research, in
simulation, and we hope it will represent the beginning of a longer

To be clear, no current CC scheme works with arbitrary scenarios.
Human-designed loss-triggered schemes do poorly if the network has big
buffers or exposes stochastic loss. Delay-triggered schemes have had other
difficulties that you noted. The best in-network schemes to date don't work
well with the varying link speeds seen in wireless links.

All of these schemes make assumptions about the network. We think it would
be better if the assumptions and goals were explicit. And if you're going
to do that, you may as well try to make the scheme be a function of those

In our paper, we showed that computers can generate congestion-control
schemes that outperform human-designed schemes over particular ranges of
simulated example networks. We publish these sets of scenarios and the
simulation setup for turnkey replication. (http://web.mit.edu/remy)

What would be cool would be if you used the Remy tool and demonstrated
concrete use cases where a computer-generated scheme could not be developed
to give acceptable performance over the whole set. That would be pretty
interesting! And then we can talk about, well, why does that happen, and
whether there is another congestion signal or search strategy we should add
that fixes the problem, or whether this represents a more fundamental

We've shown it works -- in certain ranges of scenarios. If you can show it
doesn't work in other cases, that's very interesting and would motivate
further discussion. We are trying to break it too!

Best regards,

On Thu, Sep 19, 2013 at 4:04 PM, Detlef Bosau <mail at detlef-bosau.de> wrote:

> Unfortunately, the discussion I wanted to initialte did not really start
> perhaps due to the difficulties with some posts?
> Nevertheless, I would appreciate any comment on my remarks.
> Thanks,
> Detlef

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