Re: [PATCH RFC] batman-adv: BATMAN V: use/prefer 11s airtime link metric

[Marek Lindner <marek.lindner@mailbox.org>]

On Saturday, 18 January 2025 03:00:07 CET Andrew Strohman wrote:
> The second problem I have, seems to be that sta_get_expected_throughput()
> returns a bandwidth which is an over-estimate. For example, it
> estimates 150Mb/s. But really, I'm only getting 25Mb/s, or less on the
> link. I *think*
> the expected bandwidth delivered by minstrel is not considering the
> fact that the
> radio cannot tx as often as it would like due to contention. The return
> value seems to reflect that fact that we tx to the sta at a high rate,
> but doesn't reflect the fact that it's hard to get an opportunity to tx.

It is important to point out that batman-adv is not trying to get an 
'accurate' knowledge of the throughput. The throughput metric is an estimate 
and the important aspect is that the method of estimating the throughput is 
consistent across all radios on the same AP. This is necessary to make the 
estimated throughput values comparable. At the end of the day, the routing 
algorithm has to make an informed decision about which route is better, not 
getting the most accurate throughput measurement.

Please also keep in mind that the accuracy of any 'measured' throughput value 
over WiFi is temporary (in real world setups). If you measured 5 minutes later 
you might get a different throughput value due to interference, traffic from 
other mesh participants, the weather, etc.

FYI, expected throughput and also 802.11 throughput estimation are taking 
congestion into account. If you believe this isn't sufficient to get an accurate 
read of the situation, can you please expand on your findings? Note that the 
data rate fallback (tx rate / 3) is the exception to this rule.


> HWMP doesn't need to consider this, because it only supports one radio. 

Where do you see the difference to expected throughput? Expected throughput and 
data rate also is per radio and neighbor. 


> I found that adding a 2.4ghz radio to my bat interface has caused 
> instability and poor performance compared to just running batman with the
> 5ghz radio only.

With batman-adv throughput metric the 5GHz radio should be preferred due to 
the higher throughput of the radio. Can you please share details about your 
setup and highlight why you believe 2.4GHz is chosen over 5GHz.

Cheers,
Marek