Scan wifi card on linux when connected-

[Dan Williams]

On Wed, 2007-05-30 at 12:44 -0700, hong zhang wrote:
> when driver scans, it will scan all channels as
> default. Driver supports about 32 channels on a/b/g.
> Default scan time on each channel is 100ms. It takes
> at least 3 seconds to complete scan job. If client is
> associated with AP, for example at channel 6. If scan
> is allowed, driver will leave channel 6 when it scan
> on other channels. Unless AP konws driver is canning
> and AP buffers packets for more than 3 seconds.
> Otherwise, packets will be lost.
> 
> So I think normal scan is not allowed when connected.

So that's you answer then, as to why it's not returning scan results
when it's connected.

If the driver is smart, it will send the AP a power save enter frame, do
the scanning, then tell the AP it's woken up again, then get all the
buffered packets from the AP.

Or, the driver could scan 2 or 3 channels, then hop back to the
associated channel for a small amount of time to talk to the AP, then do
the next set of channels.

The driver should be keeping a list of scan results from previous scans
to return when iwlist gets called, and aging those scan results to
delete each BSS when a certain amount of time has elapsed since the last
beacon has been seen from that BSS.

In any case, if the driver doesn't allow scans while connected, that
driver is dumb and broken and should be made smarter.

Dan

> --- Dan Williams <dcbw at redhat.com> wrote:
> 
> > On Wed, 2007-05-30 at 10:31 -0700, hong zhang wrote:
> > > Magda,
> > > 
> > > When client is already associated with AP, iwlist
> > will
> > > not do scan (normal scan). You can disaasociate
> > with
> > > the AP and run iwlist again. See any difference.
> > To 
> > > verify what I said. You can put printk() on
> > > ieee80211_notify_scan_done(struct ieee80211vap
> > *vap)
> > > to prove scan is done when iwlist is executed.
> > 
> > Sounds like a driver bug; if you look in the source
> > for the SIOCSIWSCAN
> > handler, does it dis-allow a scan when connected?
> > 
> > Dan
> > 
> > > 
> > > ----henry
> > > --- magda chelly <sandra26899 at yahoo.fr> wrote:
> > > 
> > > > Hello,
> > > > 
> > > > I'm trying to scan a wifi card on debian
> > > > distribution,
> > > > (armel:nokia n800), but with iwlist scan, it
> > doesn't
> > > > show me all the networks, the connected one,
> > does
> > > > not
> > > > appear and others are missing.
> > > > Can someone help me please.
> > > > 
> > > > Thanks,
> > > > Magda,
> > > > 
> > > > 
> > > >      
> > > >
> > >
> >
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