User guide

Table Of Contents

4-45

Radio Interface

The access point implements QoS using the Wi-Fi Multimedia (WMM) standard.

Using WMM, the access point is able to prioritize traffic and optimize

performance when multiple applications compete for wireless network

bandwidth at the same time. WMM employs techniques that are a subset of the

developing IEEE 802.11e QoS standard and it enables the access point to inter

operate with both WMMenabled clients and other devices that may lack any

WMM functionality.

Access Categories – WMM defines four access categories (ACs): voice, video, best

effort, and background. These categories correspond to traffic priority levels and

are mapped to IEEE 802.1D priority tags. The direct mapping of the four ACs to

802.1D priorities is specifically intended to facilitate inter operability with other

wired network QoS policies. While the four ACs are specified for specific types of

traffic, WMM allows the priority levels to be configured to match any

network-wide QoS policy. WMM also specifies a protocol that access points can

use to communicate the configured traffic priority levels to QoS-enabled wireless

clients.

Table 4 WMM Access Categories

WMM Operation – WMM uses traffic priority based on the four ACs; Voice,

Video, Best Effort, and Background. The higher the AC priority, the higher the

probability that data is transmitted.

When the access point forwards traffic, WMM adds data packets to four

independent transmit queues, one for each AC, depending on the 802.1D

priority tag of the packet. Data packets without a priority tag are always added to

the Best Effort AC queue. From the four queues, an internal “virtual” collision

WMM Access Categories

Access