Description
This article describes how to use FortiAP load balancing.
Scope
FortiGate and FortiAP running versions 7.4.X and up.
Solution
If enabled, Wireless controller will monitor the number of connected devices across FortiAP, and try to balance connected devices if there is a nearby FortiAP and those are close enough to be 'heard' above a certain level by WiFi Devices, and the connected device number exceeds the configured threshold.
It is possible to configure the handoff RSSI value threshold.
Handoff RSSI is measured over a generic floor noise value of -95 dBm from the nearby FortiAP.
To initiate FortiAP load balancing over -68 dBm, configure this value to 27.
As an example in this configuration on ap profile:
config wireless-controller wtp-profile
edit FAP-profile
set ap-handoff enable
set handoff-sta-thresh 20
set handoff-rssi 27
set max-client 30
end
If the radio receives more than 20 stations, it will look for the stations with the lowest signal below and start to move those to FortiAPs that could better serve them, redirecting to those stations that can be connected to over -68 dBm, but only if there is a FortiAP nearby that can 'hear' those stations at said level.
It is also possible to configure a hard limit per FortiAP. In this case, FortiAP will reject new device associations upon reaching 30 devices connected to it.
Consider that FortiGate will only attempt to balance the first time. If the Wi-Fi device still sends an association request to the same FortiAP, this one will accept it in order to avoid device 'bouncing' between two FortiAPs all the times.
As a best practice, the RSSI value should be set between 25 to 30 for voice-multimedia traffic to minimize handoff interruptions, but between 23 to 27 for regular data. This assumption is based on a Wi-Fi network network design that supports the required signal strength for voice applications.
For a good Wi-Fi experience, always consider FortiAP and device capabilities, as well as the types of applications to support. For example, if it is necessary to support multimedia conference over Wi-Fi for 1x1 Mimo devices, 10 devices per radio/FortiAP should not be exceeded due to channel utilization at low association rates. However, it is possible to increase this threshold if the supported Wi-Fi devices are 2x2 or better, up to double the supported device number as channel utilization decreases by using higher association rates.
Keep in mind that the weakest device connected to a FortiAP radio will set the overall performance for all devices on the same cell.
