Re: [PATCH RFC] mac80211 default tx_last_beacon false (congestion)

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2010-12-09 at 13:15 -0800, Tim Harvey wrote:
> The 802.11 spec states that the STA that generated the last Beacon frame shall
> be the STA that response to a probe request.  This is important for congestion
> reduction when a probe request is received - only 1 node in an adhoc BSS
> will transmit a response.  While mac80211 drivers should provide the
> tx_last_beacon function to report if they transmitted the last beacon many
> do not.  As an attempt to reduce probe response congestion default this
> to 0 such that a node not implementing this capability does not contribute
> to unnecessary congestion.
> 
> In a modern medium sized office environment I see upwards of 100 probe
> requests per second received at a given node from various hardware/OS/drivers
> doing zeroconf 'active probing' as opposed to passively listening for beacons.
> With a modest 10-node adhoc network consisting of drivers that do not implement
> this tx_last_beacon feature, I have seen this result in the simultaneous xmit
> of probe responses accumulating to 500 probe responses per second because of
> collisions which brings the adhoc network to its knees as well as causes
> needless congestion.

FWIW, I'm OK with this. It shouldn't really have much adverse effect.

johannes