[Starlink] [Rpm] [LibreQoS] [EXTERNAL] Re: Researchers Seeking Probe Volunteers in USA

[Sebastian Moeller]

Hi Jeremy,

> On Mar 13, 2023, at 16:08, Jeremy Austin <jeremy at aterlo.com> wrote:
> 
> 
> 
> On Mon, Mar 13, 2023 at 3:02 AM Sebastian Moeller via Starlink <starlink at lists.bufferbloat.net> wrote:
> Hi Dan,
> 
> 
> > On Jan 9, 2023, at 20:56, dan via Rpm <rpm at lists.bufferbloat.net> wrote:
> >
> >  You don't need to generate the traffic on a link to measure how
> > much traffic a link can handle.
> 
>         [SM] OK, I will bite, how do you measure achievable throughput without actually generating it? Packet-pair techniques are notoriously imprecise and have funny failure modes.
> 
> I am also looking forward to the full answer to this question. While one can infer when a link is saturated by mapping network topology onto latency sampling, it can have on the order of 30% error, given that there are multiple causes of increased latency beyond proximal congestion.

	So in the "autorates" a family of automatic tracking/setting methods for a cake shaper that (in friendly competition to each other) we use active measurements of RTT/OWD increases and there we try to vary our set of reflectors and then take a vote over a set of reflectors to decide "is it cake^W congestion", that helps to weed out a few alternative reasons for congestion detection (like distal congestion to individual reflectors). But that dies not answer the tricky question how to estimate capacity without actually creating a sufficient load (and doubly so on variable rate links).


> A question I commonly ask network engineers or academics is "How can I accurately distinguish a constraint in suppl from a reduction in demand?"

	Good question. The autorates can not, but then they do not need to as they basically work by upping the shaper limit in correlation with the offered load until it detects sufficiently increased delay and reduces the shaper rates. A reduction n demand will lead to a reduction in load and bufferbloat... so the shaper is adapted based on the demand, aka "give the user as much thoughput as can be done within the users configured delay threshold, but not more"...

If we had a reliable method to "measure how much traffic a link can handle." without having to track load and delay that would save us a ton of work ;)

Regards
	Sebastian


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