Re: [RFC v2 13/12] cfg80211/mac80211: allow management TX to not wait for ACK

["Arend van Spriel" <arend@broadcom.com>]

On 10/28/2011 11:28 AM, Helmut Schaa wrote:
> On Fri, Oct 28, 2011 at 11:10 AM, Arend Van Spriel <arend@broadcom.com> wrote:
>>>> I would expect this to affect the duration field in the
>>>> 802.11 header to indicate the shorter use of the medium.
>>>> Going through your patch I am not sure this is done.
>>>
>>> Hmmm. You're right, but that's something we already need to fix in many
>>> cases -- as the duration field is overwritten by most hardware these
>>> days, we haven't always maintained it very well.
>>
>> If the station still does the ACK we should not touch the duration field
>> in this case (see my reply to Helmut).
> 
> The reason is the following: if you're running a mac80211 AP with multiple
> bssids, hostapd will answer to broadcast probe requests sent by STAs with
> one probe response per bssid (unicast of course). And since some clients
> stay only for a short amount of time on the scan-channel (a few ms) under
> some circumstances the probe responses aren't sent out yet before the
> scanning STA leaves the channel and thus retried till the maximum retry
> limit is reached. And these retries consume quite a lot of airtime. And to
> avoid this we just don't want to retry the probe responses in that case.
> 
> Helmut
> 

Hi Helmut,

That makes perfect sense. Indeed not doing retries will obviously save
airtime. Thanks for taking time to explain the scenario.

Gr. AvS