Re: [Bloat] geoff huston's take on BBR

["Bless, Roland (TM)" <roland.bless@kit.edu>]

Hi,

Am 12.06.2018 um 07:09 schrieb Matthias Tafelmeier:
> On 06/12/2018 02:42 AM, Toke Høiland-Jørgensen wrote:
>>> https://ripe76.ripe.net/presentations/10-2018-05-15-bbr.pdf
>> "More research needed". Naturally ;)
>>
>> (But yeah, good points overall)
> 
> Interesting. Potentially, all affectuated. After having applied the BBR
> 2.0, we might are back to Cubic? :D

I don't understand what you're saying. I think Geoff tested BBR v1.0.
Explanations for the experienced behavior can be found in our paper
http://doc.tm.kit.edu/2017-kit-icnp-bbr-authors-copy.pdf, esp. section
3. Geoff's findings in the wild nicely confirm our results that were
performed in more controlled lab settings. Important is though, that
you always test with multiple concurrent BBR flows...

> Moreover, if it tends to be unstable on larger scale - what is Google
> doing then? Thought they've got a more or less homogeneous BBR driven
> TCP flow ecosystem - at least internally!? Was all propaganda? When
> speculating, might working for them since of centrally handled flow
> steering approaches - "imposing inter-flow fairness".

There are certain situations where BBR might work well:
1) you only have a single flow at the bottleneck, might be the case in
their B4 scenario
2) The senders a application limited (e.g., YouTube)
3) The bottleneck buffer is much larger than a BDP
   (then BDP will limit the queue size between 1 and 1.5 BDP)
However, BBR has no explicit fairness mechanism, so sometimes
one will see quite unfair shares for longer periods,
even if there are only BBR flows present at then bottleneck.

Regards
 Roland