Airtime fairness

WiFi has a natural tendency for clients farther away or clients at lower data rates to monopolize the airtime and slow down overall performance. Airtime fairness helps to improve the overall network performance in these conditions.

Airtime fairness has the following characteristics:

• Only applies to downlink traffic.
• Can be set on both 2.4 GHz and 5 GHz radio bands.
• Can be set per-SSID. Each VAP is granted airtime according to the percentage assigned to the VAP.
• Can apply to all kinds of VAP (Bridge, Tunnel, or Mesh) and all kinds of authentication (Open, PSK, or Enterprise).
• Only applies to data and is not for control or management.

Airtime fairness is balanced from the TX side of the AP to the client since that's the only direction under the control of AP.

For example, there are two Bridge mode SSIDs with a wireless client and an airtime fairness weight of 80% and 20%. When traffic travels from the Ethernet to the wireless client, the traffic for each SSID matches the airtime fairness weight assigned to them.

Airtime fairness is not related to SSID type or authentication type. The following example uses Bridge mode SSID and Open Authentication security.

To set the airtime fairness weight in SSID - GUI:

To set airtime fairness weight from the GUI, you must enable Advanced Wireless Features viability (see Advanced Wireless Features).

1. Ensure Advanced Wireless Features is enabled.
2. Go to WiFi and Switch Controller > SSIDs and select the SSID you want to apply airtime fairness weight to.
3. Scroll down to Advanced Settings.
4. In Airtime weight, enter the weight you want.
5. When you are finished, click OK.

To set the airtime fairness weight in SSID - CLI:

The default atf-weight is 20 so there is no need to set this option for atf_br2.

config wireless-controller vap
    edit "atf_br1"
        set atf-weight 80
        set ssid "atf_br1"
        set security open
        set local-bridging enable
        set schedule "always"
    next
end

config wireless-controller vap
    edit "atf_br2"
        set ssid "atf_br2"
        set security open
        set local-bridging enable
        set schedule "always"
    next
end

To enable airtime fairness in radio:

This example uses one FAP-S423E unit with airtime fairness enabled on the 5 GHz radio band.

config wireless-controller wtp-profile
    edit "S423E_atf"
        config platform
            set type S423E
        end
        config radio-1
            set mode disabled
        end
        config radio-2
            set band 802.11ac
            set airtime-fairness enable
            set vap-all disable
            set vaps "atf_br1" "atf_br2"
            set channel "149"
        end
        set ext-info-enable enable
    next
end

config wireless-controller wtp
    edit "PS423E3X16000029"
        set admin enable
        set wtp-profile "S423E_atf"
        config radio-2
        end
    next
end

To verify the airtime fairness weight from FortiAP:

PS423E3X16000029 # cw_diag -c atf
Airtime Fairness Info:
 interface                              ssid  configured-atf     applied-atf
    Radio 0 ATF disabled
    Radio 1 ATF enabled
    wlan10                         atf_ssid1              80              80
    wlan11                         atf_ssid2              20              20

PS423E3X16000029 # wlanconfig wlan10 showatfinfo
                    SHOW  RADIO  ATF  TABLE  
WLAN:SSID/Client(MAC Address)      Air time(%)    Config ATF(%%)   Assoc
 wlan10:atf_ssid1                       80.0            80.0   
 wlan11:atf_ssid2                       20.0            20.0   
 ------:Unallocated Airtime              0.0  

Verify the airtime fairness weight from real traffic

When two similar clients connect with two SSIDs, downlink traffic is passed from Ethernet to the wireless client with the same bit rate.

This example shows that tx_bytes from atf_br1 is almost four times higher than atf_br2.

To view traffic statistics from SSID1:

PS423E3X16000029 # cw_diag -d vap 90:6C:AC:8A:66:10
  VAP extension info
Radio 1 VAP 0:
    tx_packets                   : 60543
    tx_bytes                     : 70608777
    tx_data_packets              : 60543
    tx_data_bytes                : 70608777
    tx_datapyld_bytes            : 68308143
    tx_ucast_data_packets        : 57462
    tx_mbcast_data_packets       : 3081
    tx_discard                   : 94193

To view traffic statistics from SSID2:

PS423E3X16000029 # cw_diag -d vap 90:6C:AC:8A:66:11
  VAP extension info
Radio 1 VAP 1:
    tx_packets                   : 18839
    tx_bytes                     : 19731946
    tx_data_packets              : 18839
    tx_data_bytes                : 19731946
    tx_datapyld_bytes            : 19016064
    tx_ucast_data_packets        : 15760
    tx_mbcast_data_packets       : 3079
    tx_discard                   : 84924