WLAN Design question

Unanswered Question
Aug 8th, 2007

If you have an area with 40+ wireless users...how can you setup 3 AP's in that area and set it up so that they are somehow load balanced.

I'd like to have all 3 AP's sharing the load so to speak.

I have this problem too.
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ericgarnel Wed, 08/08/2007 - 18:16

We need more info in order to help you...

such the freq in use b,g or a, the size of the area, will the users roam, percent of overlap, bitrates required,etc...

rfountain Thu, 08/09/2007 - 05:59

We are using 1231G's so b/g. The size of the area is about 50K sq feet. Many users however are clustered in one area.

I guess my real question is, if I cluster 3 1231G AP's in one area, using channels 1,6 and 11; how do I get the load of client associations [for the most part] evenly balanced between the ap's?

andrew.brazier@... Thu, 08/09/2007 - 06:41

It's very difficult to control client roaming as this is something that the client PC decides. There is very little you can do to the AP config to affect the clients roaming behaviour. If the APs are quite close together you could try reducing the transmit power to keep the area covered by each AP as small as possible so there is minimum overlap. The only other thing (which is a bit tedious) would be to hard code each client to connect to a particular AP but this would only really work if the clients didn't move around.

It would be a good idea to do a survey and see how much overlap there is between APs at different transmit power levels, this will help you keep overlap to a minimum.

rfountain Thu, 08/09/2007 - 07:06

But isn't overlap ok so long as you are using channels 1,6 and 11?

I thought if you only have 3 ap's overlap isn't an issue so long as you used 1 6 and 11.

andrew.brazier@... Thu, 08/09/2007 - 07:15

Using 1, 6 & 11 prevents interference between the APs. If you have too much overlap then clients may "flap" between APs and you will have little control of which client connects to which AP. Keeping the transmit power as low as possible will ensure that any one client (hopefully) will only "see" one AP at a time and they won't all pile onto one AP.

ericgarnel Fri, 08/10/2007 - 14:07

Prevent is the keyword here.

I was playing around with one of my APs (lwapp) and manually set the power all the way up. I was able to witness the client flapping Andrew mentions. I did notice that my radio on my Dell D600 had less issues than 2 Dell D400s at the same table. Just goes to show you that not all client radios are equal. I set the one AP back to global control and My connection was stable enough to stream music over the wireless and one of the Dell D400s worked fine, while the other still had issues.

Blame it on card drivers, service paks, phase of the moon,etc.

Both my Dell 600 & d610 are dual boot with XP & Ubuntu and I get better connectivity with Ubuntu

While at Cisco Networkers this year, they had 3 APs mounted on the same easel and had placed a few of the AP/easels around the conf center.

It seemed to work fine for the most part, but I was not privy to the config they were using.

scottmac Sat, 08/11/2007 - 06:12

Using 1, 6, and 11 will prevent interference between the APs as mentioned.

The hook is whether any other APs or wireless equipment within range are using any of those channels / frequencies ... they will interfere, and be interfered with, any other devices on thoses channels / frequencies.

For example, if users set up "Ad-Hoc" networking on channel 1, the AP (and all clients within range) on channel 1 will see the interference.

The other thing is that there is no way to truely "load balance" with all of the APs, regardless of the channel if they are all on the same SSID.

Depending on your circumstances, you may want to implement a "Red, Green, Blue" system where (by whatever method you choose) access is given to the users on a rotating / round-robin basis; some users are on teh "Red" net, some are on the "Green" net, some are on the "Blue" net.

Having different SSIDs per AP is the only way you can guarantee that users X ends up on network segment in a balanced load.

There are a couple different ways to cause the users to pick up their assignment automatically, but if the users are fairly static, it is probably easier in the long run to just assign the network manually(and put a color dot on the client, so when they call with a problem you can ask what color their on).

Remote areas can support all three SSIDS on one AP since the probable load is likely to be less.

Good Luck



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