Selective scanning solution

Jouni Malinen jkmaline
Sat Mar 26 21:44:42 PST 2005

On Wed, Mar 23, 2005 at 07:27:17AM +0100, Marcin Dabrowski wrote:

> 	But :), I don't know how can I find the right moment to start
> scanning. Is there any function which is called when station looses
> connectivity or which measures channel parameters permanently ??

Unfortunately not in host_roaming=2 mode.. I'm not aware of any reliable
way of finding out that the connection is lost. RID FD43 (CommsQuality)
could be polled for signal quality information, but it looked like
firmware just stopped updating this if no more packets were received
from the current AP. In theory (but not necessarily always in practice),
signal strength could drop just before the connectivity is lost, so
polling this RID could be enough to trigger full scan.


I just added support for selecting which channels to include in the
scan. The current development snapshot from CVS includes new parameter,
scan_channels (e.g., iwpriv wlan0 scan_channels 0x00ff) that is used to
mask channels for scans (iwlist wlan0 scan).

In addition, I fixed an issue with scan requests in host_roaming=2 mode.
Previously, data connection died when this was done. Now the connection
is restored automatically by re-joining (which does not actually do
anything else than fixes firmware state).

This allows background scans, e.g., when using wpa_supplicant. It's also
a step towards making roaming work for this case. For now, it would be
possible to run something like 'while true; do iwlist wlan0 scan; sleep
60; done' to make the client eventually roam. I'm also looking into
making host_roaming=1 work with wpa_supplicant since this mode should
generate events notifying connection loss and would thus allow faster

Jouni Malinen                                            PGP id EFC895FA

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