WMM (Wi-Fi Multimedia)

Windows Mobile 6.5
A version of this page is also available for
4/8/2010

Wi-Fi Multimedia (WMM, formerly known as Wireless Multimedia Extensions) refers to QoS (Quality of Service) over Wi-Fi. QoS enables Wi-Fi access points to prioritize traffic and optimizes the way shared network resources are allocated among different applications. Without QoS, all applications running on different devices have equal opportunity to transmit data frames. That works well for data traffic from applications such as web browsers, file transfers, or email, but is inadequate for multimedia applications. Voice over Internet Protocol , video streaming, and interactive gaming are highly sensitive to latency increases and throughput reductions, and require QoS networks. WMM prioritizes traffic demands from different applications and extends Wi-Fi's high quality end-user experience from data connectivity to voice, music, and video applications under a wide variety of environment and traffic conditions. WMM defines four access categories (voice, video, best effort, and background) that are used to prioritize traffic so that these applications have access to the necessary network resources.

WMM provides differentiated services for networking applications running over IPv4, by tagging the layer 3 and layer 2 protocol layer bit fields. This is to enable applications which need to have preference over other traffic on the network to work with minimal interference from other traffic running at lower network priority.

802.1p is a traffic-handling mechanism for supporting QoS in local area networks (LANs). 802.1p2 defines a field in the layer-2 header of 802 packets that can carry one of eight priority values. Typically each transmitted packet will be marked with the appropriate priority value. Devices on the network are expected to treat the packets accordingly (by making use of underlying queuing mechanisms). The scope of the 802.1p priority value is limited to the LAN. Once packets are carried off the LAN, through a layer-3 device, the 802.1p priority is removed.

Diffserv3 is a layer-3 QoS mechanism. It defines a field in the layer-3 header of IP packets, called the diffserv codepoint (DSCP)4. Typically, hosts or routers sending traffic into a diffserv network will mark each transmitted packet with the appropriate DSCP. Routers within the diffserv network use the DSCP to classify packets and apply specific queuing or scheduling behavior (known as a per-hop behavior or PHB) based on the results of the classification.

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