3Com WL-603 - Manual (Page 71)

Wireless Settings 69
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:
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.
Access Category WMM
Designation Description
802.1D
Tags
AC_BE (AC0) Best Effort Normal priority, medium
delay and throughput. Data
only affected by long delays.
Data from applications or
devices that lack QoS
capabilities. 0, 3
AC_BK (AC1) Background Lowest priority. Data with no
delay or throughput
requirements, such as bulk
data transfers. 2, 1
AC_VI (AC2) Video High priority, minimum
delay. Time-sensitive data
such as streaming video. 5, 4
AC_VO (AC3) Voice Highest priority, minimum
delay. Time-sensitive data
such as VoIP (Voice over IP)
calls. 7, 6