[Server-devel] Technical questions

James Cameron quozl at laptop.org
Thu Jan 21 16:58:11 EST 2010

On Thu, Jan 21, 2010 at 04:18:24PM +0100, Eustace Amah wrote:
> One of the problem that am experiencing now is that I configured the
> 15 APs with same ESSID, different channels(1,6,11) shared among them
> and located all around the school. Remember that the APs are
> configured with different subnet from the lease of DHCP server but
> when more than 3 XO tries to connect it knocks everyone out
> immediately. The APs are PoE enabled. The models are Cisco Small
> Business Model WAP4410N. I have increased the power to the APs.
> Any solution to this?

There's not enough problem data above to reduce the possible causes to
something workable, but I can suggest data to capture and a way to test
for one particular problem.

Additional problem data needed:

- what does "knocks everyone out immediately" mean?  Are other wireless
  users losing connectivity?  Do the XO laptops remain associated
  (left-hand LED on)?  Do the APs remain accessible through their web
  interface during the symptom?

- what does "iwlist eth0 scan" show on an XO laptop?  (Start Terminal,
  become root, type "script scan.log", press enter, type "iwlist eth0
  scan", press enter, repeat the scan a few more times, type "exit",
  send me the scan.log file),

Testing for too many APs:

- turn off 12 APs leaving three running on different channels; does the
  symptom still occur?  You can skip this test if it is impractical.
  The purpose of the test is to prevent noise in the commons.

- reduce the transmit power on all APs to the minimum value; does the
  symptom still occur?

I've reviewed the WAP4410N product specifications [1].  The XOs will be
operating 802.11g, so that is the important thing to look for in the
specifications.  The WAP4410N has 2 dBi antenna, transmit power of up to
17.5 dBm, and receiver sensitivity of -73 dBm.

The specifications suggest it is an indoor unit.  Check your
environment; make sure the product is not being operated below 0 degrees
C, above 40 degrees C, or above 85% humidity.

I wasn't able to find what the current firmware version is, because I've
no obligation from Cisco.  You should check to see if a firmware upgrade
is available.


1.  http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10047/ps10052/data_sheet_c78-501860.html


> -----Original Message-----
> From: Martin Langhoff [mailto:martin.langhoff at gmail.com] 
> Sent: Thursday, January 21, 2010 1:09 PM
> To: James Cameron; akleider at sonic.net; Reuben K. Caron; taiwo.alabi; Eustace Amah; server-devel at lists.laptop.org; Emeka Lewis Nwankwo; kene.ijezie
> Subject: Re: [Server-devel] Technical questions
> On Thu, Jan 21, 2010 at 12:28 PM, Martin Langhoff
> <martin.langhoff at gmail.com> wrote:
> > 3 - Define how many users you can connect to an AP -- some APs have
> > "configured" hard limits in the software they ship. If you have to
> > guess, assume ~40 as the upper limit.
> Let's reword that as: assume 30, which is where most APs start having
> problems. If you are using OpenWRT, you can probably support 40. If
> you have tested your AP, then you'll know for real.
> In general, it is very hard to go over 40 active nodes per channel;
> this is mainly due to limitations of "sharing the commons" of the
> radio spectrum.
> High end APs may be able to operate different antennas in different
> channels -- so one AP acts as if it were 3, working on 1, 6 and 11.
> cheers,
> m
> -- 
>  martin.langhoff at gmail.com
>  martin at laptop.org -- School Server Architect
>  - ask interesting questions
>  - don't get distracted with shiny stuff  - working code first
>  - http://wiki.laptop.org/go/User:Martinlanghoff

James Cameron

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