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

Bob McMahon bob.mcmahon at broadcom.com
Mon Apr 18 19:02:13 EDT 2016

Another way might be to think about it from the fairness scheduler
perspective - compute a "benefit ratio" for each end device where the
denominator is the information that would be transferred using a legacy
rate (theoretical) and the numerator is the actual information transferred
to that device, all normalized on some unit of time (1 second?)   It's
similar to efficiency but gives a multiplier indicating how well fairness
algorithms are working.


On Mon, Apr 18, 2016 at 3:48 PM, David Lang <david at lang.hm> wrote:

> 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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