Re: IEEE80211 Acknowledgement

[Johannes Berg <johannes@sipsolutions.net>]

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On Mon, 2009-05-04 at 18:55 +0200, Ivo van Doorn wrote:
> On Monday 04 May 2009, Johannes Berg wrote:
> > On Mon, 2009-05-04 at 18:35 +0200, Ivo van Doorn wrote:
> > 
> > > Well I believe the idea would be that (I'll see if I can dig up a reference
> > > to the initial discussion about this feature on this list) the driver sets a flag
> > > that mac80211 needs to keep a list of all frames send out to the driver and
> > > listens for ACK's.
> > > 
> > > As soon as a ACK was passed from driver to mac80211 it could check if
> > > the corresponding frame 
> >       ^^^^^^^^^^^^^^^^^^^
> > 
> > Here's the problem. What I'm saying is that there's no way to knowing
> > what the "corresponding frame" is.
> 
> Hmm, so would there be any alternatives of fixing this problem?

The proper way of fixing this would be a firmware upgrade ;)

Working around it would be possible if the driver queued only a single
frame to the hardware, when it knew the frame needed ACK status, and
flushed all queues before that frame, so it knows exactly about the
frame... This has HUGE overhead and performance impact though, and
requires lots of work in mac80211 to not request status for every frame
to start with.

Since this breaks hostapd operation quite significantly, and I don't see
hostapd changing to accommodate this since that essentially breaks the
ability to be spec compliant (I'm fairly certain some places require
checking for ACK).

An easier way would be to fake a ACK reception in the driver for every
frame...

johannes

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