Q

Do multiple APs on the same channel cause wireless cards to jump between them?

We use an 802.11 G wireless network for 20 users using two Linksys 54G wireless access points. Each laptop has a Linksys 54G wireless PCMCIA card installed, and we utilize both access control lists and 128-bit WEP encryption for security.

The connection between a user and the access point drops, but we have configured both points on the same channel, so the user automatically picks up the next access point.

Is the use of two access points on the same channel causing the wireless cards to jump from one access point to the next, and do you have any recommendations on how to improve connection stability?
Unless your APs are very distant from each other, tuning both access points to the same channel probably IS causing co-channel interference, resulting in sub-optimal performance. This may or may not be the primary cause of connection dropping, but it's certainly something you will benefit from fixing.

To create an extended service set composed of multiple access points, all APs should be assigned the same Service Set Identifier (ESSID). Each access point should be assigned a non-overlapping channel, which is selected to minimize co-channel interference. For example, adjacent 802.11b/g access points should be tuned to channels 1, 6 or 11. In larger WLANs, it is impossible to avoid channel re-use since there are so few non-overlapping channels. Just minimize interference by keeping APs with the same channel as far apart as you can while providing adequate coverage -- for example, here is a large area covered by eight APs:

AP (Ch1)          AP (Ch6)          AP (Ch11)          AP (Ch1)

         AP (Ch11)       AP (Ch1)              AP (Ch6)          AP (Ch11)
When APs are far enough apart, stations nearest to each AP will stick with that AP. Stations located in an area served by several APs with approximately the same signal strength may still roam between "equivalent" APs. On stations experiencing that problem, consider configuring the station to use a preferred AP. Your Linksys cards may not have this option, but many other cards do (e.g., Cisco350).
This was first published in July 2004

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