CHAPTER 5: SYSTEM CONFIGURATION
The access point implements QoS using the
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
Table 3 WMM Access Categories
WMM Access Categories
Access | WMM |
Category | Designation |
AC_VO (AC3) | Voice |
AC_VI (AC2) | Video |
AC_BE (AC0) | Best Effort |
AC_BK (AC1) | Background |
Description
Highest priority, minimum delay.
High priority, minimum delay.
Normal priority, medium delay and throughput. Data only affected by long delays. Data from applications or devices that lack QoS capabilities.
Lowest priority. Data with no delay or throughput requirements, such as bulk data transfers.
802.1D Tags
7, 6
5, 4
0, 3
2, 1
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