Re: How many SSIDs can be listed?

[Robert Moskowitz <rgm htt-consult com>]

Yo Derek! Fancy meeting you here. I will look you up later.

Derek Atkins wrote:
> There's another problem. The wireless extensions have a size limit
> for the scan results data. The buffer size is a u16, which means you're
> limited to 65535 bytes. The network manager buffer increase algorithm
> keeps doubling the buffer size, so you get 2k, 4k, 8k, 16k, 32k, 64k..
> but 64k mod 2^16 == 0! Meaning you never actually get to try a full 64k
> buffer.
>
> A workaround to this issue is to change the NM code to max out at
> 65535 instead of 65536 or "100000" (which is the current limit)..
>
> This is being a MAJOR problem to a bunch of us at the IETF because
> we can easily hear well over 100 APs most of the time.
Please! We are use to seeing some of the worst-case work environments 
with too many APs and SSIDs for most code to cope with.
> Quoting Dan Williams <dcbw redhat com>:
>
> > On Mon, 2008-03-10 at 23:40 -0400, Robert Moskowitz wrote:
> > > Ver 0.6.4 in Centos 5.1
> > >
> > > I am seeing 17 SSIDs in the current list. But I am not seeing one that
> > > I expected to see. And some of the listed SSIDs are 'stale'; that is
> > > they were visible in the part of the hotel I was in a couple minutes
> > > ago, but not in this part. So I guess a second question is how do you
> > > force a scan to produce a current SSID list?
> >
> > You don't force a scan. NetworkManager will periodically scan with a
> > backoff algorithm; it will start at 20 seconds and back off to 2
> > minutes. APs are kept in the scan list for a maximum of 6 minutes
> > before being culled.
> >
> > The problem is that wireless is hard, and sometimes cards/drivers miss
> > beacons. Often they will not report all the APs that are known to be
> > around at a given time. So NetworkManager takes a composite of the last
> > few scans as the scan list.
> >
> > 0.6.x also combines APs with the same SSID in the UI. 0.7 splits them
> > out at the NetworkManager layer, while the applet combines APs that are
> > similar based on more than just SSID (SSID, security settings, band,
> > channel).
> >
> > > Perhaps the question may be how many APs can be handled and then those
> > > are turned into the SSID list (when more than one AP per SSID is found
> > > as in the case of some of these SSIDs).
> >
> > Are any of the APs hidden?