[PATCH] scan: evaluate AP-reported channel load

[David Bauer]

Hi Jouni,

thanks for your review.

On 10/15/21 11:22 PM, Jouni Malinen wrote:
> On Sun, Oct 03, 2021 at 07:04:05PM +0200, David Bauer wrote:
>> When determining the expected throughput from a AP, take the AP-reported
>> channel utilization (QBSS Load element) into consideration.
> 
> While it would be nice to do something like this to be able to use that
> information from the AP, this specific way of doing that would seem to
> have a significant risk of penalizing any AP that supports this
> capability compared to APs that do not provide any indication which
> would be processed as if they had advertised 0% channel load. That does
> not feel correct and could result in selecting worse candidates.

Good point, this is indeed a problem in the current state.

> 
> I would also point out that at least the last time I did some testing
> between vendor implementations, the reported values were completely
> different between two APs on the same channel in more or less the same
> location in the test setup.. In other words, I would not place much, if
> any, trust in this value being something that could be compared between
> two different APs. The only thing that seemed to be more or less
> comparable was the values from the same AP device in a sense that the
> channel load value increased when there was more traffic on the
> channel..
> 

Just to be sure - do you dislike the idea of implementing the Channel 
load at all or do you think It's better if we cap the impact at some 
value (50% of throughput)?

I'm aware the implementation on the AP side vary widely. However, when 
having a multi-AP setup with multiple identical APs with multiple 5GHz 
radios operating on different frequencies (e.g. a lecture hall), 
selecting a BSS with lower load is preferable IMHO.

I also thought about comparing based on connected Stations, however this 
would require a larger refactoring of the selection code.

Best
David