New APs and poor load balancing

We are a school, with two C25 controllers (I'll call them A and 😎 serving about 45 3705i APs, deployed about one per 2 or 3 classrooms. All classrooms get decent signal strength (-50 to 60 dBm or higher), usually from multiple APs -- but we are increasing the AP density in some areas in order to reduce load per AP during periods of high client density such as online testing sessions.

We recently added two APs in one area already served by two other APs on controller A. The newly added APs joined themselves to controller B. All APs have exactly the same VLAN and SSID config, and most clients had usable signal strength from at least three APs. We did NOT try to set all the APs up as a load-sharing group.

The first time we had a high client load in this area (about 25 devices per AP), we noticed that over 90% of the clients were getting on the original APs with only a few on each of the new APs. All APs show the same signal strength (max 13 dBm).

Any idea why only a tiny fraction of the clients are connecting to the new APs?

Another question: The group of APs is not literally "line-of-sight" since they are in different rooms separated by sheetrock-on-metal-stud walls, but they do overlap. Should we configure them as a load-sharing group, even if it means moving either the original or the new APs from one controller to another to get all of them on the same controller?

Thank you in advance for any advice!

6 replies

Have you tuned ALL of the APs since you have deployed the new APs (power and channel)? What version of code are you running on the C25?
Jeremy Gibbs wrote:

Have you tuned ALL of the APs since you have deployed the new APs (power and channel)? What version of code are you running on the C25?

Thank you for your quick reply.

We put the new APs in active mode to let them optimize channels. Not sure if that's what you mean by "tuned".

Controller code is v09.21.02.0014
Userlevel 7
Hello Steve, there are some settings you can enable in 9.21 code that can help like probe suppression and adjusting the minimum basic rate of the radio. Load balance may also be an option. You should contact the GTAC for further assistance and design suggestions.
A load sharing group needs the APs to have line of sight. I don't think it will help in your case. Minimum Basic Rate helps you determine whether the AP still services a device or not, no matter the coverage area (defined by the transmit power). This functionality together with load balancing (band steering) helps achieving the performance you are looking for.
Userlevel 3
Maybe the AP the most clients sick to is the one they see first by entering the room or so. IF all APs have an equal signal strength, many wireless clients will not roam themselves.
So load-balancing groups can help.
Userlevel 1
From your description it doesn't look like you actually want load want the clients to attach to a "better" AP. To make that happen you need to make the closest AP the "best" option. You can do that with a few settings. Turn down the power on the APs so the do not broadcast as far, set the minimum basic rate high enough that only devices close to the AP will connect and verify you have correct channel usage. You might have to disable some 2.4gz radios if you have many in a small area. Also, if you had good wireless coverage and then added APs, you might need to move some of the original APs. Anytime you add/remove APs it can change what you need as far as placement goes.