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

[Dan Williams <dcbw redhat com>]

On Wed, 2006-07-12 at 14:38 -0500, Robo Blaster wrote:
> Thanks for the info on scan behaviour. I was worried, because my list wasn't changing. It may be that the madwifi driver's scan routine usually finds the same ones.
> 
> > Wireless scans are never complete or reliable on _any_ platform.
> 
> I meant to stress the comparison of using the AP_SCAN parameter in wpa_supplicant. Using wpa_supplicant directly, when AP_SCAN is 2, I get associated almost immediately. When it is 1, wpa_supplicant looks for a match in the truncated scan results, and almost always fails. I certainly don't blame NM if the wireless card doesn't return the AP I want, but maybe NM could fallback to AP_SCAN=2 if the first scan list returned to wpa_supplicant does not have an SSID match.

I actually consider the AP_SCAN stuff in wpa_supplicant to be pretty
much broken.  There is just no good rule on when to use 1 or 2, plus
these bits of wpa_supplicant more or less duplicate what NM is doing
already.  I forget the specifics of which drivers do and do not work
with AP_SCAN 1 or 2, but it seems to me we should usually be using
AP_SCAN = 2.  In fact, we used to use AP_SCAN = 2, but changed it in Feb
to 1 because madwifi had problems with that.  Yay for madwifi.

Dan

> -Robbo
> 
> > ----- Original Message -----
> > From: "Dan Williams" <dcbw redhat com>
> > To: "Robo Blaster" <ijustmadethisup mail com>
> > Subject: Re: Limit on number of APs? Some way to force-rescan?
> > Date: Wed, 12 Jul 2006 15:02:55 -0400
> > 
> > 
> > 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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> > > >
> > >
> > >
> 
> >
> 
>