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98 Operation
Chapter 4 - System Configuration
mechanism first selects data with the highest priority to be granted a transmit
opportunity. Then the same collision resolution mechanism is used externally to
determine which device has access to the wireless medium.
For each AC queue, the collision resolution mechanism is dependent on two
timing parameters:
AIFSN (Arbitration Inter-Frame Space Number), a number used to calculate
the minimum time between data frames
CW (Contention Window), a number used to calculate a random backoff time
After a collision detection, a backoff wait time is calculated. The total wait time is
the sum of a minimum wait time (Arbitration Inter-Frame Space, or AIFS)
determined from the AIFSN, and a random backoff time calculated from a value
selected from zero to the CW. The CW value varies within a configurable range. It
starts at CWMin and doubles after every collision up to a maximum value,
CWMax. After a successful transmission, the CW value is reset to its CWMin
value.
For high-priority traffic, the AIFSN and CW values are smaller. The smaller values
equate to less backoff and wait time, and therefore more transmit opportunities.
To configure WMM, select the Radio Settings page, and scroll down to the WMM
configuration settings.
Figure 4-21:
WMM Backoff Wait Times