Re: Network Manager drops wireless connections

[Dan Williams <dcbw redhat com>]

On Mon, 2006-01-16 at 21:56 +0000, Chris Jones wrote:
> > When the device is up, does 'iwlist eth1 scan' show any results?  If it
> > does, but NM doesn't, then I think that's a bug in NM.
> 
> Hi,
> 
> When I run  'iwlist eth1 scan'  the results vary. Sometimes I get 

Scan results are never 100% accurate.  They depend on the card hopping
between channels and waiting for a particular time period, listening for
an access point to broadcast the beacon.  If the card doesn't wait long
enough, or you're near the fringe of the AP, or the moon is in the 4th
day of its waning, you won't see the AP.

NM tries to work around this by aggregating results of a few different
scans, and only removing an AP from the scan list when it hasn't been
noticed in a scan for a few minutes.  The algorithm isn't perfect right
now and APs get dropped too quickly IMHO, but that's the tradeoff
between scanning more often (and sucking power on the laptop) vs. a more
accurate network picture.

Moral: no single scan represents the network topology.

> Does this indicate my signal strength is weak ( I did recently move my 
> wireless station a little, although it is still next door about 5 metres away 
> so pretty close)? NM always reports exactly 100% on the icon applet, which 
> does now I think about it seem a little odd - Shouldn't it occasionally dip a 
> little ? ( Also, I have NEVER had the little bar charts working when I left 
> click on the applet - IS this also something I should worry about ? )

This likely doesn't indicate odd signal strength, but probably that the
wireless driver you're using (ipw2100) doesn't accurately report it to
NetworkManager.  In any case, 5m is pretty close and should be around
75% - 100% anyway unless there's a lot of interference.  You can see
what the card actually thinks if you do 'iwconfig eth1' and look for the
"Link Quality=100/100" bit.

The signal strength bars in the chart are for scanned networks, while
the applet icon is for the currently connected network.  Unfortunately,
they come from two completely different sources and at two completely
different times, so the strength will be different even for the AP
you're currently associated with.  Fact of life, really.  Also many
drivers don't report scanned signal strength either, or report it in
completely wrong units, which was the case for most drivers until quite
recently.  It needs a driver fix.

Dan