[PATCH] hostapd: add check for overlapping legacy BSS

[Rajkumar Manoharan]

On Mon, May 12, 2014 at 06:28:26PM +0300, Jouni Malinen wrote:
> On Sat, May 03, 2014 at 07:56:07PM +0530, Rajkumar Manoharan wrote:
> > Before bringing up 20/40 MHz BSS, a scan is triggered to identify
> > overlapping BSS. If there is any legacy BSS present within the affected
> > range, then 40 MHz operation should be rejected and BSS should start
> > with 20 MHz.
> 
> Why would we do that? What's so different about legacy (as in "non-HT"
> in this case) BSS and HT 20 MHz BSS that would justify such difference?
> Can you please point me to the rule in the IEEE Std 802.11-2012 20/40
> coex requirements that this patch implements?

IEEE Std 802.11-2012 - 10.15.12: Switching between 40 MHz and 20 MHz

An FC HT AP 2G4 shall reevaluate the value of the local variable 20/40
Operation Permitted (see 10.15.3.2) when either of the following events occurs:
	? A BSS channel width trigger event TE-A is detected.
:
:

TE-A: On any of the channels of the channel set defined in Clause 19, reception
of a Beacon frame that does not contain an HT Capabilities element.

-Rajkumar