Wireless Multimedia Extensions


Wireless Multimedia Extensions, also known as Wi-Fi Multimedia, is a Wi-Fi Alliance interoperability certification, based on the IEEE 802.11e standard. It provides basic Quality of service features to IEEE 802.11 networks. WMM prioritizes traffic according to four Access Categories : voice, video, best effort, and background. However, it does not provide guaranteed throughput. It is suitable for well-defined applications that require QoS, such as Voice over IP on Wi-Fi phones.
WMM replaces the Wi-Fi DCF distributed coordination function for CSMA/CA wireless frame transmission with Enhanced Distributed Coordination Function. EDCF, according to version 1.1 of the WMM specifications by the Wi-Fi Alliance, defines Access Categories labels AC_VO, AC_VI, AC_BE, and AC_BK for the Enhanced Distributed Channel Access parameters that are used by a WMM-enabled station to control how long it sets its Transmission Opportunity, according to the information transmitted by the access point to the station. It is implemented for wireless QoS between RF media.

Power Save Certification

The Wi-Fi Alliance has added Power Save Certification to the WMM specification. Power Save uses mechanisms from 802.11e and legacy 802.11 to save power and fine-tune power consumption. The certification provides an indication that the certified product is targeted for power critical applications like Mobile/Smart Phones and portable power devices
The underlying concept of WMM PowerSave is that the station triggers the release of buffered data from the access point by sending an uplink data frame. Upon receipt of such a data frame the AP releases previously buffered data stored in each of its queues. Queues may be configured to be trigger enabled,, and delivery enabled,. Queues refer to the four ACs defined for WMM.