3Com 3CRWER300-73-US User Guide - Page 68

66 CHAPTER 5: CONFIGURING THE ROUTER 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. The following table explains the four access categories: Access Category WMM Designation Description 802.1D Tags AC_BE (AC0) AC_BK (AC1) AC_VI (AC2) AC_VO (AC3) Best Effort Background Video Voice Normal priority, medium 0, 3 delay and throughput. Data only affected by long delays. Data from applications or devices that lack QoS capabilities. Lowest priority. Data with no 2, 1 delay or throughput requirements, such as bulk data transfers. High priority, minimum 5, 4 delay. Time-sensitive data such as streaming video. Highest priority, minimum 7, 6 delay. Time-sensitive data such as VoIP (Voice over IP) calls. AIFS (Arbitration Inter-Frame Space) - The minimum amount of wait time before the next data transmission attempt. Specify the AIFS value in the range 0-15 microseconds. CWMax (Maximum Contention Window) - The maximum upper limit of the random backoff wait time before wireless medium access can be attempted. The contention window is doubled after each detected collision up to the CWMax value. Specify the CWMax value in the range 0-15 microseconds. Note that the CWMax value must be greater or equal to the CWMin value.