What is WMM ?

WMM is qos mechanism used in 802.11 wifi system. WMM clients have 4 AC queues. WMM clients will classify the traffic and use these queues when they are associated with a WMM-enabled AP. WMM clients will behave like non-WMM clients—map all traffic to the Best Effort (BE) queue when it is associated with Non-WMM enabled AP.

The prioritization of the traffic on the downstream (for example, from wired to wireless) and on the upstream (for example, from wireless to wired) is dictated by the configuration of the WLAN Service and the QoS tagging within the packets, as set by the wireless devices and the host devices on the wired network.

Categories of wireless traffic to 4 Access criteria are as below according to priority defined on 802.1p field  

Access point will also mark wired qos header based on the WMM AC of the frame it received from wireless.QOS value can be 802.1q Tag, but in case untagged packet it will be marked using DSCP in the ip header. DSCP to 802.1p mapping table looks like below.

Beside WMM, other type of Qos mechanism can be used on wlan as below.

• 802.11e — If enabled, the AP will accept WMM client associations, and will classify and prioritize the outbound traffic for all 802.11e clients. The 802.11e clients will also classify and prioritize the inbound traffic.
• Turbo Voice — If any of the above QoS modes are enabled, the Turbo Voice mode is available. If enabled, all the out traffic that is classified to the Voice (VO) AC and belongs to that VNS is transmitted by the AP via a queue called Turbo Voice (TVO) instead of the normal Voice (VO) queue. The TVO queue is tailored in terms of contention parameters and number of retries to maximize voice quality and voice capacity.
• U-APSD— Unscheduled Automatic Power Save Delivery feature works in conjunction with WMM and/or 802.11e, and it is automatically disabled if both WMM and 802.11e are disabled.

Below figure shows the configuration page of QOS on WLAN in Identfi system.

Below figure shows the configuration page of QOS on WLAN in WiNG based system.

on this configuration window, below configuration option is possible for wireless client classification.

1. WMM – Implies WiFi Multimedia QoS extensions are enabled on this radio. This allows different traffic streams between a wireless client and the Access Point radio to be prioritized according to the type of traffic (voice, video etc). The WMM classification is required to support the high throughput data rates required of 802.11n device support.
2. Voice – Optimized for voice traffic. Implies all traffic on this WLAN is prioritized as voice traffic on the radio.
3. Video – Optimized for video traffic. Implies all traffic on this WLAN is prioritized as video traffic on the radio.
4. Normal – Optimized for best effort traffic. Implies all traffic on this WLAN is prioritized as best effort traffic on the radio.
5. Low – Optimized for background traffic. Implies all traffic on this WLAN is low priority on the radio.