Re: [Bloat] [Make-wifi-fast] graphing airtime fairness in wifi

[David Lang <david@lang.hm>]

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On Mon, 18 Apr 2016, David Collier-Brown wrote:

> I haven't internalized this yet, but my instantaneous reaction is:
>
> *   a radar screen is something people have been educated to
>   understand, so that's cool, and over time, plotting the time taken
>   for something against the load in somethings is what capacity
>   planners expect to see: "_/"

I agree, but a radar screen only shows the 'now', and I'm not sure how 
interesting that really is compared to how it looks over time.

David Lang

>
> --dave
>
> On 18/04/16 06:48 PM, David Lang 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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>
>
>

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