Wireless Multimedia Extensions

To a voluntary association of more than 300 companies in the electronics industry warranty - Wi- Fi Multimedia, designated (WMM ) also known as Wireless Multimedia Extensions (WME ), one based on the IEEE 802.11e standard certification, by the Wi- Fi Alliance is of interoperability in wireless networks (WLAN) - was developed to make better use of consumer electronics and multimedia over Wi-Fi. In this way, the streaming of multimedia contents (eg IPTV or DVB- IPI) or the use of IP - telephony (eg for wireless telephony) should be optimized.

WMM provides this quality of service features ready (QoS) for IEEE 802.11 - based networks. A fixed bandwidth is not guaranteed; the traffic is divided into four categories, which are prioritized differently:

• " Best Possible " ( AC_BE )
• Background ( AC_BK )
• Video ( AC_VI )
• Language ( AC_VO )

The characteristics of each category are defined by several parameters:

• Acknowledgement Policy ( ACKPOLICY ): Defines whether the recipient is to acknowledge the receipt of a data packet.
• Admission Control Mandatory (ACM ): Defines whether the access control by the access point ( engl. access point ) or the accessing client is controlled.
• Arbitrary Inter-Frame Space Number ( AIFSN ): Defines a fixed period of time between accesses per category.
• Contention Window (CW): Defines the time window for the negotiation phase concurrent accesses. The window is determined by a minimum ( CWmin ) and maximum value ( CWMAX ).
• Transmission Opportunity ( TXOP ): This allows the prioritization of a category. A category of a higher value, for example, voice or video is given priority in data transmission. In addition, the values ​​for AIFSN and CW are to be defined correspondingly smaller.

Between two WMM -compliant devices in the DLS mode ( engl. direct link setup) can be made a direct connection. For this purpose, a device is communicated to each of the MAC address of the other device.

More than 5,000 units have been certified according to WMM.