[Bloat] geoff huston's take on BBR

[Jim Gettys]

On Tue, Jun 12, 2018 at 2:55 AM Dave Taht <dave.taht at gmail.com> wrote:

> On Mon, Jun 11, 2018 at 10:58 PM, Kevin Darbyshire-Bryant
> <kevin at darbyshire-bryant.me.uk> wrote:
> >
> >> On 11 Jun 2018, at 22:27, Dave Taht <dave.taht at gmail.com> wrote:
> >>
> >> https://ripe76.ripe.net/presentations/10-2018-05-15-bbr.pdf
> >
> > Fascinating!
> >
> > "       • BBR changes all those assumptions, and could potentially push
> many networks into sustained instability
> >
> >         • –  We cannot use the conventional network control mechanisms
> to regulate BBR flows
> >
> > • Selective packet drop just won’t create back pressure on the flow”
> >
> > And I keep on seeing questions on whether BBR understands ECN - if not….
> well I think we see the results.
>
> I think geoff goofed in his testing of BBR, starting all flows at the
> same time, thus syncing up their probing periods. Real traffic is not
> correlated this way.
> (I made the same mistake on my initial bbr testing)
>

​Beware of self synchronization...  In other situations, there have been
situations in which aggregate behavior occurs due to this phenomena.

So both synchronized and unsynchronized startup of flows under test is
actually a good idea (and watching to see if anything in the aggregate
behavior over time results in such synchronization).
                                                  - Jim
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