[Make-wifi-fast] Estimating WiFi congestion using different-prio pings

Toke Høiland-Jørgensen toke at toke.dk
Sat Jan 13 06:49:07 EST 2018

Pete Heist <peteheist at gmail.com> writes:

>> On Jan 12, 2018, at 1:33 PM, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> Some people over at Skype have implemented a technique for a client to
>> estimate congestion at the WiFi AP by pinging the AP at VO and BE
>> priority and measuring the difference in response times. Pretty neat,
>> except that it would presumably break if the AP was FQ-CoDel-enabled...
>> Paper here, including a description of the bandwidth estimation stuff
>> they apply to Skype based on the information:
>> https://dl.acm.org/citation.cfm?doid=3143361.3143390
>> -Toke
> Interesting, I wonder if this could be used to evaluate congestion
> within an ISP’s backhaul (but the article is behind a paywall).
> FreeNet Liberec currently uses SmokePing with ICMP. They have dozens
> of APs, but here’s what results look like to the AP I use:
> http://www.drhleny.cz/bufferbloat/smokeping/vysina.png
> They’re not all as rosy: http://www.drhleny.cz/bufferbloat/smokeping/studankaA.png
> When I get back to it, I want to write a SmokePing plugin for irtt to
> try in the same environment. The results may be interesting, because
> I’ve proven for myself that Ubiquiti is prioritizing ICMP, so I
> suspect that what we’re seeing in the SmokePing results is a measure
> of connectivity and maybe contention as well, but not congestion or
> user-perceived latency. And even though the ping results to my AP
> don’t vary much, I feel like web surfing latency varies considerably,
> maybe dramatically, depending on the time of day. I’d like to prove
> that.
> The summary of what they did at Skype makes me think it would also be
> interesting to see the _difference_ between ICMP and irtt (UDP at best
> effort)...

Any prioritisation of ICMP may just be because ICMP replies are
generated by the kernel, whereas other traffic goes all the way to the
userspace application generating it. However, it is certainly possible
that ICMP is being prioritised - some people do that in an effort to
game benchmarks...


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