What is Air Time Fairness?

In a modern 802.11n Wi-Fi environment, not all wireless clients transmit data at the same speed.  There may be 802.11g clients being serviced by the AP and the AP will automatically send traffic to these clients at a slower rate.  Also some clients may support a 40 Mhz channel width while others support a standard 20 Mhz wide channel.  Some clients may support 3x3 MIMO, meaning they can transmit 3 separate data streams in parallel and some Wi-Fi clients only one.  Furthermore let's not forget that as the distance between an AP and a client increases, the data rate slows down.

So, you get the picture, an Access Point serves each client not at the maximum speed the AP supports, but at the maximum speed the client supports.  Some clients are very fast, some clients are very slow.

Having this diversity of speed capabilities is generally unavoidable in wireless LANs but it causes a problem of sorts.  The Access Point can only handle traffic from one client at a time* so each station must wait it's turn to forward data to the AP.  This happens so fast it seems as if all stations are accessing the wireless network simultaneously but in fact, they are serviced one at a time.  Since a slow station uses far more of the network time sending traffic than a faster station does, the slower stations tend to dominate the network and the faster stations receive less of the APs time.  

It makes you wonder, why have fast wireless clients in your WLAN when the slower clients drag down network throughput for everybody?

Ruckus Wireless has solved this problem with a feature called Air Time Fairness. Instead of allocating each station a certain number of frames they can send when they communicate with the AP, the Access Point allocates media access based on time.  Normally a station sending a 1000 byte packet at 54 Mbps would access the media for a far greater time than a station sending the same packet at a 300 Mbps data rate.  By allocating access based on time and not the number of frames, the slow stations no longer drag down network throughput and the faster stations realize substantial increased in data throughput.

Air Time Fairness is enabled by default in all Ruckus Wireless Access Points.  Air Time Fairness adresses an issue few people think about but it's a serious issue that causes wireless LANs to fail to perform as well as they can.  

* A dual band Access Point can service two clients at once.