Signal outage on AP1250's with LWAPP-Image

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Apr 24th, 2008
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Hi,

i'm experiencing a problem with several AIR-AP1252AG-E-K9 converted to LWAPP:

If i run AirMagnet in order to monitor the signal of the AP, i see a signal outage approximately every 20 seconds, but not in regular intervals. At the time of this gap, one ping to a wlan-station gets lost and voice-over-wifi (7921) gets a short outage, too.

I tried another AP1252, same problem.

An AP1242 connected to that WLC (WLC4404-100) has no problems as well as the same AP1252 with IOS.

A change of the WLC Software Version didn't make any difference, neither a change from antenna diversity to right (or left).

Anybody got an idea for the cause of this? Is the AP maybe scanning for other frequencies in that time?

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ericgarnel Thu, 04/24/2008 - 05:28
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What are you seeing in the logs? Also, do you have the controllers manage channels & power automatically? Are you seeing lots of AP disassociations from the controller?


It could also be caused by an underlying infrastructure problem at either layer2 or 3. Take a look at your switch & router logs too

SJessulat_2 Thu, 04/24/2008 - 06:15
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The log contains only messages i can correlate to other events (changes made, etc.)

I tried Auto-RF and manually set channel and power, both the same.

The AP (It's the only one on the controller at the moment) is connected to the WLC the whole time, no disassociations in the log.

I will try another controller tomorrow. Maybe that will help.

dennischolmes Thu, 04/24/2008 - 10:12
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Guys,


Could you please keep detailed records of this as I would like to start a lab recreation of the event and then forward to Cisco. I suspect an issue with the packet aggregation piece of the code. I would like to know if happens only on the 2.4 radio or 5 ghz. Also, is high throughput enabled? What version of code? etc.

Scott Fella Thu, 04/24/2008 - 18:51
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I heard of this issue also when surveying using the 1252's.... haven't tried it yet, but I do have implementations in which users ftp video which can take up to 45 minutes.... no issues there.

SJessulat_2 Thu, 04/24/2008 - 23:47
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Thanks for your replies.

@ Dennis:

I just tried another WLC (2106) and the problem occurs, too. The Code versions are 5.0.148.0, but i tried 4.2.112.0 as well.

I also switched to 5GHz, and it seems like there are no problems. BUT i cannot guarantee this, because our AirMagnet-Software only supports 802.11b/g monitoring, so i could only test it by talking over the WiFi-Phone and simultaneously pinging it.

dennischolmes Fri, 04/25/2008 - 03:03
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Thanks for the info guys. I will make sure to get this to the Business Unit. I am starting my own testing and it seems to be a problem in the packet aggregation piece of the 802.11n standard for this AP. If you turn off high throughput it seems to dissapate but hey, that's why you buy 802.11n right? I'm betting that is one of the reasons, other than the obvious ones( more non-overlapping channels), they push you to 5ghz.

SJessulat_2 Fri, 04/25/2008 - 04:33
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I just tried to turn off High Throughput, but the problem persists.

I unchecked the box "11n mode" under 802.1b/g/n -> High Throughput. Is this enough?

Scott Fella Fri, 04/25/2008 - 04:58
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Try to allow or disable WMN and see if that helps. If you disable high throughput, disable WMN. If you have high throughput enabled then enable WMN.


What client card are you using and do you have 40MHz channel width or 20MHz channel width?

Scott Fella Sun, 04/27/2008 - 13:41
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I meant WMM which is wifi multi media. it is requied if you want to run 40MHz channel width. To disable the mixed mode, 802.11 B data rates have to be disabled.


I have tested the 1252 in both autonomous and LWAPP and I can't seem to see those timouts.

Dennis,


Doesn't Legacy-OFDM support PLCP Header protection for g clients, and could the problem be with the switching between 20 and 40-wide channels in the presence of g and n clients? Sounds like this could be a 2.4GHz backwards compatibility issue. This is not a draft-N requirement.


dennischolmes Sun, 04/27/2008 - 18:07
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I hadn't thought of that. You know, you could be right there. I need to do some investigating in my lab. Kudos on a change in thought process there.

SJessulat_2 Fri, 12/19/2008 - 03:44
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Hi,


I think i have to bring this thread back up:


I just installed the new WLC-Software 5.2.157.0 and added an AP-1252 to it. The signal outages are still occuring while our 1242s are working fine.


Did anyone find a solution to this problem, yet? I would like to use these APs on our Controller very much, but with problems like this it is quite impossible.


Otherwise i think i have to wait for our 1140 to arrive for testing.


Greets,

Sebastian

SJessulat_2 Fri, 01/09/2009 - 05:10
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New year, new situation:


we just received an LAP1142.

I added it to the controller and it shows the same behavior:

Monitoring with AirMagnet shows a good signal and all of a sudden the signal is gone for about half a second. After that, the signal comes back up and remains good for some time.

This happens twice a minute sometimes and other times the signal stays up for almost 5 minutes.


Overall, this is the situation:

AP1242s work fine with the controllers.

LAP1242s work fine with the controllers.


AP1252s work fine in autonomous mode.

LAP1252s show the problem with the controllers.


LAP1142s show the problem with the controllers.


So only 802.11n-compatible Access Points show these problems, and only with the Lightweight Image.


Anybody experiencing the same problems?

Or anybody working with LAP1252s which don't show these problems?


Greets,

Sebastian

ERNIE DULANOWSKY Mon, 03/02/2009 - 09:24
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Hi:

I have encountered this problem in one of our installations that uses 1252 APs.

We had originally loaded the WLC with 4.2.130, but I upgraded to 4.2.176 to see if it would help with some issues a particular client device was having. The clients were AMX panels, and no, it didn't help. The short drops were noticed almost immediately, so we regressed to 4.2.130, and have not had the problem reoccur. We haven't tried any 5.2 releases yet.

Leo Laohoo Mon, 03/02/2009 - 13:19
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I'm not seeing anything like that right now. I've got 1252's joined to a 4402 (5.2.178.0 FW, 4.2.112.0 True Bootloader). 1252 are running HREAP and I've got a 7921 constantly hooked to it.

Leo Laohoo Wed, 03/04/2009 - 15:37
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What does the logs say? Does it say that the radios were reset?

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