[Cerowrt-devel] [bbr-dev] taking apart BBR's behaviors in flent

Neal Cardwell ncardwell at google.com
Wed Sep 21 15:45:28 EDT 2016

On Wed, Sep 21, 2016 at 3:25 PM, Dave Taht <dave.taht at gmail.com> wrote:
> > So it seems my intuition was wrong, at least for these scenarios. It wasn't
> > CUBIC that would kill BBR, it's the other way around.
> My intuition was that "delay based TCPs can't work on the internet!" -
> and was wrong, also.

Keep in mind that BBR is not really "delay-based", at least in the
traditional sense. BBR is not based on backing off in response to a
single signal like loss or RTT increases. If BBR could be said to be
"based" on any one thing, it's "model-based": it has a model of the
network with two parameters: bottleneck bandwidth and round-trip
propagation time. So delay increases do not always lead to a slower
sending rate or lower volume of data in flight. For example, if the
round-trip propagation delay increases but the bandwidth stays
constant, BBR can actually increase the amount of data in flight in
order to achieve its fair share of the bandwidth available in the
longer pipe.

Thanks for all this testing!


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