Periodic scanning and larger beacon timers.

Jouni Malinen j at w1.fi
Tue Jan 25 11:18:27 EST 2011


On Mon, Jan 24, 2011 at 04:11:41PM -0800, Ben Greear wrote:
> I'm currently using an AP with beacon timer of 240.  I believe this is
> beyond the normal dwell time for passive scans, and what I'm seeing is
> that occassionally, wpa_supplicant gets into a state where it scans every
> 5 seconds but doesn't ever find the AP.

Which channel are you using? With active scanning, it there should be no
problems in finding the AP. However, with passive scanning, such a long
beacon interval can certainly cause problems.

> Any opinions on adding some randomization to the scan timers so that
> they cannot get stuck in a dead zone between beacons?

Which scan timer are you talking about? wpa_supplicant does not
currently control the dwell time or exact timing of channel changes
during the scanning operation. As such, this would likely apply more to
the driver/kernel 802.11 stack implementation than wpa_supplicant.
Changing the about five seconds timer in wpa_supplicant is unlikely to
have noticeable difference since it is not exact five seconds between
each scan, but five seconds after the previous scan was completed and I
would fine it surprising if you can synchronize this with any AP beacon
operation (those are in TUs, not milliseconds and for example, that 240
TUs would be 245.76 ms).. Anyway, if you can show that changing this
would really have a noticeable effect in real life, I would have no
problems adding random 0..999999 usec extra delay to that wait period..

-- 
Jouni Malinen                                            PGP id EFC895FA


More information about the HostAP mailing list