Tuning "roaming"

Jouni Malinen j
Sat Sep 15 22:16:30 PDT 2012

On Tue, Sep 11, 2012 at 11:03:22AM -0500, Dan Williams wrote:
> We've had exactly the same problem with some of our larger customers.
> If you're using background scanning, and have a lot of access points,
> you'll certainly hit this problem of ping-ponging between APs on each
> scan which increases the possibility of an 802.1x auth failure.

There's something else wrong, too, if you have issues with IEEE 802.1X
authentication failures frequently enough for this to make a noticeable

> If Jouni thinks that the current signal thresholds shouldn't be changed,
> then a patch to let them be adjusted via the configuration is probably
> the best way to go.  FWIW I'm using:
> dbm < -75 :: min_diff = 4
> dbm < -70 :: min_diff = 6
> dbm < -65 :: min_diff = 8
> else min_diff = 15
> for a modified wpa_supplicant_need_to_roam() in events.c.

The current values are not really based on any real research, i.e., I
picked them as a reasonable initial step to reduce unnecessary jumps
between BSSes. As such, they can certainly be changed. That said, I'm
not sure it would be good to avoid roaming in some cases, so I would
rather not make these too large with the current design.

It could be useful to still allow roam to happen over time even if the
difference is relatively small if the signal strength of the current AP
is not good enough to provide more or less maximum throughput. This
would obviously need some additional information to be maintained over
time (e.g., moving average of the signal strength in the BSS table).

Jouni Malinen                                            PGP id EFC895FA

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