I have a rectangular auditorium with 2 APs diagonally and 1 AP outside as a backup. The 2 APs inside are identical C9120AXE. But sometimes I have a very uneven client distribution. For example, 50 clients on the AP1 5GHz band and 1 on AP2. Now:
- AP1 5 GHZ: 50 clients, channel 52-56, power 15 dBm, noise -93
- AP2 5GHz: 1 client, channel 112-108, power 20 dBm, noise -92
I have load balancing disabled due to some issues in other zones. What can I do to avoid this? Why do all clients prefer AP1? Is the channel a factor?
Once a client associates with an AP, then it will roam to another AP when RSSI goes below a threshold level that triggers a roam. (there are other triggers too, eg retransmit rate, beacon loss, channel utilization, etc)
Apple iOS clients it is -70dBm
For Samsung clients it is -75dBm
In your case most likely, when a client device enters to room, they may get better RSSI from AP1 and associate with it. Irrespective of where the client device goes within the room, it may still get strong RSSI (>70dBm) from AP1. In that scenario, even you get a very strong RSSI from AP2, there is no reason to raom to AP2 as those triggers are not met.
You have to reduce cell area (either using a directional antenna) or reduce power (if omni) to see if that helps the client to roam to next AP.
If users turn-off wifi & turn-on once they are settled inside the room, most likely they will connect to those two AP with much better distribution, again it may not be a practical solution due to inconvenience to users.
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I would reduce power of both AP, let's say 11dBm on 5GHz. that should help to the client to trigger roam if they walk away from AP1 (assume their RSSI go below -70/75dBm marks)
2.4GHz radio power has to ~8dB less than that of 5GHz to make 2.4GHz less attractive (otherwise the client will think 2.4GHz is better)
Regarding UNII bands, yes most of the clients scan for UNII-1,2,3 first only scan UNII-2 extended channels once in every 5th or 6th scan cycle. This could impact roaming time, if they purely rely on active or passive scanning (most of today's network enable for 11k/v, so clients can ask AP better roam AP for a client to go with.