[PROPOSAL] Add hostapd.conf parameter to skip checkforneighboring BSS (prevent fallback in 150Mb mode)

Jouni Malinen j
Sun Apr 8 08:08:42 PDT 2012

On Sun, Apr 08, 2012 at 01:49:38PM +0300, Valeriy Kucherenko wrote:
> I guess that this is my case. Hostapd won't start in 40 mhz mode if any overlapping BSS is found on 13+9 channel,

That would need to be another 40 MHz BSS with different
primary/secondary channels..

> but the main problem, as I write before, is that even if it starts in 40 mhz mode (clients shows 270-300 mbps connection), 
> then from time to time it fallback in 20 mhz mode (clients shows 150 mbps connection). I can't understand why this happens,
> but it happens. And after overriding scan results with oper40 = 1; this problem seems to go away.

Have you verified that the AP Beacon frames are indeed changing at that
point or is this based just on what a client may show based on whatever
mechanism implemented at that device? hostapd does currently update the
HT Protection field dynamically based on what kind of stations are
around it in the operating channel, but I don't think it even has
capability of disabling 40 MHz mode without a restart..

> Anyway, you wrote that hostapd check for overlapping BSSes only at startup. Let's assume that at the moment of start there was one
> conflicting BSSes on our channels, so as result hostapd started in 20 mhz mode. Then, after some time this conflicting AP has 
> gone away (this is an example from real life). In this case, I guess, hostapd will still work in 20 mhz mode and will not switch 
> into 40 mhz mode because check for neighboring BSSes performed only at startup. Am I correct?

Yes, that's the current implementation. This will hopefully get more
dynamic in the future to allow 20/40 MHz mode to be enabled (and also
disabled) automatically based on periodic scans by the AP and/or
associated stations indicating that conflicting device leave/enter the
radio range.

Jouni Malinen                                            PGP id EFC895FA

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