Help with cleints losing there connection.

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Oct 8th, 2007
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We have approx. 100 wireless scanners and 15 Phones in a warehouse environment; we seem to be having problems with clients losing there wireless signal. The clients seem to stall when working and it takes them any where from 10 sec to a couple of minutes to reconnect, that?s if they reconnect at all. The warehouse has roughly 6 miles of conveyor that travel throughout the building. The warehouse is 3 floors with metal flooring on all floors, there are a lot of conveyor motors that are causing radio interference. The building is filled with all kinds of parts...rubber tires to metal gears. The building has 10 AP's throughout the warehouse on separate floors, we are using Cisco 1200 series AP?s and we are running WPA/PSK. The phones seem to work the same way the radios work (no figure).

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Overall Rating: 5 (3 ratings)
ericgarnel Tue, 10/09/2007 - 05:41
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A few questions:

Do you have aggressive load balancing turned on?

You may want to turn it off.

Are the 1200s in autonomous mode or lightweight mode (using WLC)?

If using lightweight mode, do the client mac addr show up in the excluded clients list when they cannot connect?

Which wireless are you using - 802.11b g or a ?

Do the clients lose connectivity when stationary or when roaming?

What other frequencies are nearby?

Does this happen at a particular time(s) of day?

dennischolmes Tue, 10/09/2007 - 17:10
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First, let's get to the root of the problem. Most connections dropped while in session are the result of multipath issues or lack of usable spectrum. This is especially true when in manufacturing environments with lots of metal occlusions. Are you using omni directional antennae? Are they diversity based? The rule of thumb is -65rssi cells with a 20-30% overlap achieved with at least 80% directional patch antennae. The reason for the patches is that they lower the noise floor significantly. Next, if using lwapp, make sure you meet LWAPP minimum best practices deployments. How big of an area are you covering? I'm betting you are way under deployed and that the deployment you have is mostly omni antennae mounted near steel posts or I beams. Try diversity patch antennae mounted 15 feet up the wall with a 10 degree down angle and then fill in the coverage holes with omnis. Of course a good spectrum analyzer such as the new CISCO Cognio piece would give you some really good answers.

keithuchida Wed, 10/10/2007 - 04:19
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OK thanks all for the replys... Yes we are using omni antennas, we are using the rubber duckies and the 5.2 dbi antennas. Yes they are diversity based. We are trying to cover roughy 500,000 sq. feet. the building is also 3 stories, all of the racking is metal, along with the flooring between all 3 floors. We have had a couple of wireless surveys done on the building, with totally different counts of what we needed to cover our warehouse. One company says 9 the other says 24????? I have run the AirMagnet surveyor, and it shows that we probably have to much overcoverage. When we try to fix that problem we end up having a lot of dead spots with in certain depts. of the warehouse. Some of the AP's are deployed near steel beams, but there are a lot that are hanging from the top of the 1st floor, in the middle of our conveyor run. We did have a Cisco Wireless tech come in and he couldnt believe that we had coverage as good as we do, his words were "We have a enviroment that he would consider RF Hell".

keithuchida Wed, 10/10/2007 - 04:25
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I will check to see if we have load balancing turned on/off. We have installed the 1241 AP's. We run 802.11 G. It seems that the clients lost connectivity when roaming with some that do complain about the signal when they are stationary. It seems to happen a lot more when the warehouse is busier then not. In the morning, there are fewer problems then the afternoon.

dennischolmes Wed, 10/10/2007 - 05:00
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24 seems like the better number for the size and scope of your deployment. Density of APs go very high in deployments such as yours when using LWAPP. You might also go into the security settings and enable caching of credentials as this will allow for quicker roams. I think however, you are underdeployed for the amount of multipath that you would experience. If you send me your floor drawings I could run them through a predictive tool and see what I come up with. My gut is that you have a large noise floor, several multipath issues, and poor coverage from the client's point of view. Remember, the client is a low powered device with little to no gain antennae. THe site survey should have been built for synchronous power settings. 40mW client equals 40mW transmission power on the APs. This assures balanced communications.

keithuchida Fri, 10/12/2007 - 12:33
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Can you send me your email address, I really dont want to post our building prints on Cisco.

Thanks for the help and advise!


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