Re: Limit on number of APs? Some way to force-rescan?

[Dan Williams <dcbw redhat com>]

On Wed, 2006-07-12 at 13:51 -0500, Robo Blaster wrote:
> It would be nice if opening the scan list triggered a rescan. In crowded AP areas, I often have problems getting connected. A contributing problem is that AP_SCAN always equals 1 if the ssid is in the scan list. A new scan is taken, my AP isn't there (usually), and it waits, scans again, and times-out. Shouldn't it rescan quicker and eventually try AP_SCAN=2 before the timeout? At least if I click "Connect to Other Wireless Network" and re-enter credentials I should get a directed scan, but if the ssid hasn't aged out of the drop-down list, it will still scan and look for an ssid match.

Actually, it does.  When you drop the menu down, NM schedules a scan in
a very short period of time, and reduces the inter-scan interval to 20s.
When you haven't touched the menu for a while, it pushes the scan
interval out to 20 minutes or something like that.

Dan

> It looks like the scan list returns 15 APs, so in an area of 25-50 APs, a directed scan will often be required.

Yes; wireless is inherently unreliable and you may not get every AP on
every scan for various reasons.  You never will, even with 'iwlist ethX
scan', even executed multiple times.  It Just Doesn't Work That Way.  So
what NM does is collect scan results and age them; an AP is removed from
the NM scan list when it hasn't been seen in a scan for 6 minutes, which
is > 3 scan requests.

Wireless scans are never complete or reliable on _any_ platform.

Dan

> -Robbo
> 
> 
> > ----- Original Message -----
> > From: "Derek Atkins" <warlord MIT EDU>
> > To: networkmanager-list gnome org
> > Subject: Limit on number of APs?  Some way to force-rescan?
> > Date: Wed, 12 Jul 2006 13:35:16 -0400
> > 
> > 
> > I'm sitting here in the IETF, and from where I sit I can hear at least
> > 15 Access Points, some A, some B/G.  I get this number by manually
> > running "iwlist ath0 scan" and looking at the results.  I see
> > "three" ESSIDS:
> > 
> > [warlord cliodev ~]$ iwlist ath0 scan | grep ESSID | sort -u
> >                      ESSID:""
> >                      ESSID:"IETF66A"
> >                      ESSID:"IETF66B"
> > 
> > However, nm-applet is only showing IETF66B, and wont let me connect to
> > IETF66A, even when I tell it to by "Connect to other wireless
> > network".
> > 
> > Now, going back to my scan-list, the IETF66A network doesn't show
> > up until "Cell 10" in my scan list.   Is there some limit to the
> > number of returns from a scan?  Does NM stop looking after some
> > point?
> > 
> > Right now I can't figure out how to tell it to connect to the A
> > network.  I can see it's there, but NM doesn't see it.  I've tried
> > restarting NM to no avail.  I haven't tried rebooting, but honestly I
> > shouldn't have to.  Is there some way to tell NM: "Hey, I know there's
> > more networks out there -- can you go look again right now?"
> > 
> > Any suggestions of things to try?  I suspect that my situation will
> > change in an hour when I move to another room.
> > 
> > -derek
> > 
> > PS: Why do I feel like I really stress test both Madwifi and NM all
> > the time with my personal usage patterns???
> > 
> > --
> >         Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
> >         Member, MIT Student Information Processing Board  (SIPB)
> >         URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
> >         warlord MIT EDU                        PGP key available
> > _______________________________________________
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> 
> >
> 
>