Re: [aqm] [Bloat] TCP BBR paper is now generally available

Neal Cardwell <> Fri, 02 December 2016 22:22 UTC

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From: Neal Cardwell <>
Date: Fri, 2 Dec 2016 17:22:23 -0500
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To: Jonathan Morton <>
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Cc: Aaron Wood <>, "" <>, bloat <>
Subject: Re: [aqm] [Bloat] TCP BBR paper is now generally available
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On Fri, Dec 2, 2016 at 3:32 PM, Jonathan Morton <>

> > On 2 Dec, 2016, at 21:15, Aaron Wood <> wrote:
> >
> > So, how is this likely to be playing with our qos_scripts and with cake?
> Cake’s deficit-mode shaper behaves fairly closely like an ideal
> constant-throughput link, which is what BBR is supposedly designed for.

Great. Yes, that's right: BBR's favorite case is a constant-throughput link
or shaper, since that's the easiest to model.

>   I haven’t read that far in the paper yet, but it shouldn’t trigger any
> “bucket detection” algorithms, because it doesn’t have a “bucket”.  It is
> capable of bursting, but only to the minimum extent required to reconcile
> required throughput with timer resolution and scheduling latency; I’ve
> tested it with millisecond timers.

That's also good to hear. If it doesn't have a "bucket" or allow
unsustainable bursts, then it should work well with BBR, and shouldn't
trigger the long-term/policer model.

Of course, if we find important use cases that don't work with BBR, we will
see what we can do to make BBR work well with them.