Brocade Mobility Access Point System Reference Guide (Supporting software release 5.5.0.0 and later) - Manual (Page 450)

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The same mechanism deals with external collision, to determine which client should be granted the
opportunity to transmit (TXOP). The collision resolution algorithm responsible for traffic
prioritization is probabilistic and depends on two timing parameters that vary for each access
category.
• The minimum inter-frame space, or Arbitrary Inter-Frame Space Number (AIFSN)
• The contention window, sometimes referred to as the random backoff wait
Both values are smaller for high-priority traffic. The value of the contention window varies through
time. Initially the contention window is set to a value that depends on the AC. As frames with the
highest AC tend to have the lowest backoff values, they are more likely to get a TXOP.
After each collision the contention window is doubled until a maximum value (also dependent on
the AC) is reached. After successful transmission, the contention window is reset to its initial, AC
dependant value. The AC with the lowest backoff value gets the TXOP.
To configure a WMM configuration for a WLAN:
1. Select the Configuration tab from the Web UI.
Select Wireless.
Select Wireless LAN QoS Policy to display a high level display of existing WLANs QoS policies.
2. Select the Add button to create a new QoS policy, or Edit to modify the properties of an existing
WLAN QoS policy.
The WMM tab displays by default.