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

[Dave Taht <dave.taht@gmail.com>]

On Tue, Jun 12, 2018 at 12:36 AM, Bless, Roland (TM)
<roland.bless@kit.edu> wrote:
> 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...

we always do that, 'round here, with flent. Glad more folk are doing it. :)

>> 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)

I think the application limited scenario is the primary one. once
typical links are fully capable of video streaming
4k video a lot of the demand for better congestion control will drop.

> 3) The bottleneck buffer is much larger than a BDP
>    (then BDP will limit the queue size between 1 and 1.5 BDP)

Sadly we still see 2sec queues on cmtses, in particular.

> 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.

except with fq at the bottleneck.

>
> Regards
>  Roland
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Dave Täht
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