Introduction
Airtime-Fairness is a feature on WLAN access points (AP) to increase the performance of faster clients in the presence of slower/legacy clients. Legacy clients need more air time to transmit/receive the same chunk of data compared to faster clients. Because of this the slower clients monopolises the airtime and brings down the throughput of the faster clients as they get lesser chance to transmit. Enabling this feature considerably improves the performance of faster clients by controlling the airtime of legacy clients.
Many legacy laptops, mobile phones, and tablets are out there which does not support the high throughput (HT) operation modes (802.11ac/802.11n). As a result the performance of the new generation wireless devices (which supports the HT operation modes) fall down when those legacy devices get connected to same WLAN network. To address this problem Cambium Networks introduces ‘airtime fairness’ on the Access points.
Supported Software Release
This feature is supported from 3.0.b24 release onwards.
Enable/Disable the feature
This feature can be enabled/disabled from the GUI or CLI of the device
- The feature can be enabled or disabled per radio (2.4GHz/5GHz)
- By default Airtime Fairness is disabled on all the radios
Enable/Disable From GUI
configure -> Radios -> select the radio drop down list -> tick “Enable Airtime Fairness”
Enable From CLI
Disable From CLI
Test results
In the test setup, one faster client (802.11ac) and a slower client (802.11a) is connected to the same access point (E400). The test is performed using iperf tool. Both UDP and TCP results are captured in the below table.
How it works?
To treat the faster and slower clients separately, there must some way to classify their packets/traffic. Airtime Fairness classifies the downlink packets (transmitted from the AP to the stations/clients) based on the following parameters
- The mode of operation of the clients.
- High Throughput mode (802.11ac, 802.11an, 802.11bgn)
- Legacy mode (802.11a, 802.11b, 802.11g)
- The band of operation (2.4GHz/5GHz)
- The Nature of the packet flow (TCP/UDP/ICMP etc.)
Once the feature is enabled on a particular radio, the traffic will be monitored thereafter and the Airtime-Fairness scheduler get activated when it sees traffic flowing from both faster and Legacy clients.
The scheduler doesn’t play any role, if the data is flowing only from faster clients or slower clients. The scheduling algorithm makes sure that the faster clients get the airtime that they deserve even when the slower/legacy clients are around.
Best practices
'Airtime Fairness' is expected to be enabled only when the slower clients are dominating the airtime and you see less speed/throughput on the faster clients which operates on 802.11n/802.11ac mode. It is not recommended to turn on the feature if the faster clients are already dominating the channel, as it may cause the legacy clients to get throttled further to give more space for faster clients, which is not fair.