[Cerowrt-devel] [Bloat] DOCSIS 3+ recommendation?

Steinar H. Gunderson sgunderson at bigfoot.com
Fri Mar 20 20:13:07 EDT 2015

On Fri, Mar 20, 2015 at 05:03:16PM -0700, David Lang wrote:
> 1. If you mark packets as congested if they have ECN and drop them
> if they don't, programmers will mark everything ECN (and not slow
> transmission) because doing so gives them an advantage over
> applications that don't mark their packets with ECN

I'm not sure if this is actually true. Somehow TCP stacks appear to be tricky
enough to mess with that the people who are capable of gaming congestion
control algorithms are also wise enough not to do so. Granted, we are seeing
some mild IW escalation, but you could very well make a TCP that's
dramatically unfair to everything else and deploy that on your CDN, and
somehow we're not seeing that.

(OK, concession #2, “download accelerators” are doing really bad things with
multiple connections to gain TCP unfairness, but that's on the client side
only, not the server side.)

Based on this, I'm not convinced that people would bulk-mark their packets as
ECN-capable just to get ahead in the queues. It _is_ hard to know when to
drop and when to ECN-mark, though; maybe you could imagine the benefits of
ECN (for the flow itself) to be big enough that you don't actually need to
lower the drop probability (just make the ECN probability a bit higher),
but this is pure unfounded speculation on my behalf.

/* Steinar */
Homepage: http://www.sesse.net/

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