User's Manual

Table Of Contents

Radio Interface

BreezeMAX Wi² and BreezeACCESS Wi² System Manual 93

Quality of Service (QoS) mechanism is required to prioritize traffic types and

provide an “enhanced opportunity” wireless access method.

The access point implements QoS using the WiFi 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 WMM-

enabled 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 (see Table 4-5). 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.

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 resolution

mechanism first selects data with the highest priority to be granted a transmit

Table 4-5: WMM Access Categories

Access