[Make-wifi-fast] graphing airtime fairness in wifi

David Lang david at lang.hm
Mon Apr 18 18:48:47 EDT 2016

On Mon, 18 Apr 2016, Dave Taht wrote:

> I have been sitting here looking at wifi air packet captures off and
> on for years now, trying to come up with a representation, over time,
> of what the actual airtime usage (and one day, fairness) would look
> like. Believe me, looking at the captures is no fun, and (for example)
> wireshark tends to misinterpret unreceived retries at different rates
> inside a txop as tcp retries (which, while educational, makes it hard
> to see actual retries)...
> Finally today, I found a conceptual model that "fits" - and it's kind
> of my hope that something already out there does this from packet
> captures. (?) Certainly there are lots of great pie chart tools out
> there...
> Basically you start with a pie chart representing a fixed amount of
> time - say, 128ms. Then for each device transmitting you assign a
> slice of the pie for the amount of airtime used. Then, you can show
> the amount of data transmitted in that piece of the pie by increasing
> the volume plotted for that slice of the pie. And you sweep around
> continually (like a radar scanning or a timepiece's pointer) to show
> progress over time, and you show multicast and other traffic as eating
> the whole pie for however long it lasts.
> conceptually it looks a bit like this:
> http://blog.cerowrt.org/images/fairness.png  (I borrowed this graph
> from  http://www.webdesignerdepot.com/2013/11/easily-create-stunning-animated-charts-with-chart-js/
> )
> Another way to do it would be to have the pie represent all the
> stations on the network, and to have the "sweep hand" jump between
> them...

does it really matter how much data is passed during the timeslice as opposed to 
just how much airtime is used? (and there will be a large chunk of airtime 
unused for various reasons, much of which you will not be able to attribute to 
any one station, and if you do get full transmit data from each station, you 
can end up with >100% airtime use attempted)

I would be looking at a stacked area graph to show changes over time (a 
particular source will come and go over time)

I would either do two graphs, one showing data successfully transmitted, the 
other showing airtime used (keeping colors/order matching between the two 
graphs), or if you have few enough stations, one graph with good lines between 
the stations and have the color represent the % of theoretical peak data 
transmission to show the relative efficiency of the different stations.

While the radar sweep updating of a pie graph is a neat graphic, it doesn't 
really let you see what's happening over time.

David Lang

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