Controller Load Balancing

Unanswered Question
Dec 5th, 2007

I have a high school that has a computer lab with 32 laptops. Also in the area are about 5 other teacher laptops. There are approximately 3 AP's in the vicinity within -72. The controller is running 4.0.179 using RRM. It seems that the computer lab is attaching to one AP only causing association and authentication failures. I can see, at one time, 28 clients on one AP, and it looks like load balancing is not functioning. I've applied the config load-balancing window 15 command with no luck, all though I have a feeling that RRM is controlling the load balancing and that command wasn't going to do much anyway. I've heard bad things about Aggressive Load Balancing so I am hesitant to turn it on.

Is there a setting I'm missing here? Or would a code upgrade solve this issue?

I have this problem too.
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john.preves Sun, 12/09/2007 - 11:23

Im not going to say there is not a way using code, but I will stand on John Chambers coffee table and tell him the only way to do this is via physical load balancing.

This requires smaller cells using data rates no lower than 11mbps and lower power settings. By limiting the cell (and adding more AP's to fix the subsequent holes) you will physically load balance the network. Turn RRM off. hard code the channels and power.

Depending on size of area and number of users, I would attempt to stick three AP's in your scenario with really small cell sizes that whose boundaries are no worse than -65dBm. When I have tweaked enough to roam from edge to middle to the other edge of the room and hit all three AP's based on should be good. Directional antennas also would play an important role here as well, shining down from the ceiling with radiation patterns kind of like spotlights. Also you would have to turn the power down on the clients or else you just have the same problem except it is now upside down.

Aggresive load balancing tends to jack up phones and possibly create a 'host flapping' situation with data clients as well. I do not use it at all.

good luck-

Richard Atkin Mon, 12/10/2007 - 01:20

Like the other post says, physical RF considerations really are the best way to go.

The other methods, like aggressive load balancing, rely upon something called CCX ( The extent to which CCX is supported depends on the code running on your wireless infrastructure, and on your client device(s).

In my experience, Aggressive Load Balancing is okay in data-only situations as TCP usually fixes any little problems without you even realising. If you're running lots of UDP / Streaming Media (like Voice / Video over Wireless) then you should definately leave ALB turned off and go down the RF planning route.

Also, RRM needs at least four APs to hear each other in order to work properly. If you don't have sufficient density to achieve this, I'd suggest you set the channel / power settings manually.




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