Re: [RFC] mac80211: fix short preamble determination

[Johannes Berg <johannes@sipsolutions.net>]

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On Mon, 2008-10-13 at 20:54 +0300, Jouni Malinen wrote:

> > I don't see how it cannot be -- you need stations not capable of
> > short-preamble to correctly update their NAV, no?
> 
> Well, if you have many such devices, yes, but one might try to live
> without such protection if there are some with very limited transmit
> needs.

Would you then announce short preamble as the AP? That'd mean all other
stations would use short preamble and the poor non-short-preamble STA
would be left completely in the dark wrt. its NAV.

>  I don't know whether it would make much sense in most cases and
> anyway, it would be possible to make APs reject all associations from
> such devices. For example, I could see an attempt to dedicate one
> channel for 11g (ERP) and short preamble supported STAs and make the
> more modern implementations get somewhat better throughput there.

Indeed, that is possible, I think there's even a status code allocated
for this.

> I'll try to remember to file a comment to TGmb on this (they are still
> collecting comments for fixing issues in 802.11 and published
> amendments). Probe Request with this does not make much sense (unless
> you are either only interested in BSSes that support short preamble
> and/or you know that the AP you're interested is able to receive this).
> Authentication, association, and public action frames might be more
> likely candidates for this.

Ohh. Just a few days ago I sent an email with a request for
interpretation (there really just is a typo in 802.11-2007 but...) That
got forwarded around a lot, but I guess at least TGmb will see it :)

johannes

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