Uneven AP client distribution in auditorium

[jmprats]

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?

Thank you

[Leo Laohoo]

At the end of the day, the wireless clients pick-and-choose which AP to join.  

[Rasika Nayanajith]

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 

https://support.apple.com/en-au/HT203068 

For Samsung clients it is -75dBm

https://docs.samsungknox.com/admin/knox-platform-for-enterprise/kbas/kba-115013403768.htm 

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.

HTH

Rasika

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[jmprats]

Thank you. I was doing the opposite, increasing the power in AP2.

Considering I have very few 2.4 GHz users, could it be a good option to enable 5GHz dual radio on AP1? Something like:

AP1: dual 5 GHz

AP2: 2.4 GHz and 5 GHz

AP3 (out of room): as  a 2.4 GHz backup AP

[jmprats]

But, it's strange, most of the clients prefer the smaller cell, because AP1 has got a transmit power of 15 dBm and AP2 20 dBm. 

Could it be related to the UNII band ?

AP 1 is using channel 52-56

AP 2 is using channel 112-108

Do clients prefer UNII-1 or UNII-2A over UNII-2C?

[Rasika Nayanajith]

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. 

HTH

Rasika

[jmprats]

I am using the following Mobility Express DCA channels configuration, do you think can be good not using all the channels in 5 GHz as I do in 2.4 GHz?