Re: IEEE80211 Acknowledgement

[Ivo van Doorn <ivdoorn@gmail.com>]

On Monday 04 May 2009, Johannes Berg wrote:
> 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...

Ok, well I'll go with this route then. Since firmware upgrades for
older hardware like rt73usb sounds very unlikely. And for rt2500usb
it is plain impossible (no firmware ;))

Alexandre: Well that seems to make your project a lot easier...

Ivo