WLAN QoS and WLAN Optimization
Domain 5 covers WMM quality of service, air-interface control and the planning choices that determine capacity rather than just coverage.
WMM
WMM is the Wi-Fi Alliance profile of 802.11e EDCA. It defines four access categories: voice, video, best effort and background. Each has different AIFSN, CWmin/CWmax and TXOP values, so voice waits less. WMM admission control can reserve airtime. QoS must be enabled end to end; DSCP mapping on the wired side is useful only if the wireless queues honor it.
Air interface control
2.4 GHz uses 1/6/11 as the non-overlapping set. 5 GHz offers many 20 MHz channels; 40/80 MHz improves peak rate but reduces reuse. In high-density areas, prefer 20 MHz, disable low rates, cap power, and use DCA/DFS where allowed. Co-channel interference is managed by layout and power, not by increasing power everywhere.
Worked example: a 60-AP auditorium with 40 MHz channels has roughly half the independent channels of a 20 MHz plan, so co-channel overlap doubles and airtime contention rises. Re-plan to 20 MHz, lower AP power, and enable band steering to 5 GHz. The peak rate per client falls, but aggregate capacity and stability improve.
Traps: high power does not equal high capacity and can create sticky clients; 40 MHz in 2.4 GHz almost guarantees overlap; WMM must be enabled on both AP and client; Bluetooth and microwave ovens are non-Wi-Fi interference.