Re: [Starlink] Network quality for rocket scientists

["Bjørn Ivar Teigen" <bjorn@domos.no>]

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Sebastian,

On Mon, 14 Feb 2022 at 17:15, Sebastian Moeller <moeller0@gmx.de> wrote:

> Hi Bjørn,
>
>
> I guess I should have started with the obvious. Nice short article!
>
Thank you!

>
> > "See the problem? Buffers produce jitter!"
> >
> > I would rephrase that as "over-sized and under-managed" buffers increase
> jitter unduly. Interestingly, bound jitter can be converted into static
> latency by using, wait for it, (delay) buffers and a scheduler.
> >
> > You are absolutely right. I was hoping someone would spot that! There is
> one problem with that approach though. To actually remove the jitter the
> scheduler can no longer be work-conserving (needs delay as you also point
> out), and that increases TCP ramp-up times (among other things). Can be a
> hard sell. I think the benefits outweigh the costs though, so I would do it
> your way.
>
>         But that is what end-points already do, on-line games do this to
> equalize internet access quality between players (allowing them to make
> matches over larger populations), as do DASH type video streaming
> applications, where the isochronous play-out takes the role of the
> scheduler and the race-to-fill-the-play-out-buffers serves to keep the
> buffers filled so the scheduler never runs "dry".


Good points. The application clients and servers can choose to use their
resources in a way that is not work-conserving and thus achieve sharing of
resources without introducing jitter. I would argue it's a different story
with the queues "in the network", in routers, switches, access points, etc.
There seems to be an unwritten law that those schedulers must be work
conserving, presumably to minimize round-trip times, and this makes it
harder to achieve well-behaved sharing. So in network devices configured to
forward packets as quickly as possible, I think it's mostly true to say
that buffers produce jitter.

        Given Pete's data at https://github.com/heistp/l4s-tests I am
> cautious to hold my breath... or to put it differently, I am certain they
> will not deliver on their promises, the bigger question is whether the
> incremental improvement they offer (over the default FIFO) is decent enough
> to retroactively justify the disruption they will have caused...


Ohh, that work has been updated a lot since the IETF showdown! Thanks for
reminding me, I'll have a look at it again.

- Bjørn Ivar


> Regards
>         Sebastian
>
>
> > >
> > >
> > > On Mon, Feb 14, 2022 at 7:07 AM Bjørn Ivar Teigen <bjorn@domos.no>
> wrote:
> > >>
> > >> Hi everyone,
> > >>
> > >> I was inspired by the latest Starship presentation to write a piece
> on network quality in the language of rocket science. The blog can be found
> here:
> https://www.domos.no/news-updates/network-quality-for-rocket-scientists
> > >>
> > >> Cheers,
> > >> Bjørn Ivar Teigen
> > >>
> > >> --
> > >> Bjørn Ivar Teigen
> > >> Head of Research
> > >> +47 47335952 | bjorn@domos.no | www.domos.no
> > >> WiFi Slicing by Domos
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> > >
> > >
> > >
> > > --
> > > I tried to build a better future, a few times:
> > > https://wayforward.archive.org/?site=https%3A%2F%2Fwww.icei.org
> > >
> > > Dave Täht CEO, TekLibre, LLC
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> >
> >
> >
> > --
> > Bjørn Ivar Teigen
> > Head of Research
> > +47 47335952 | bjorn@domos.no | www.domos.no
> > WiFi Slicing by Domos
>
>

-- 
Bjørn Ivar Teigen
Head of Research
+47 47335952 | bjorn@domos.no <name@domos.no> | www.domos.no
WiFi Slicing by Domos

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