Edimax BR-6224n Usre Manual page 59

AC_BK: Background (low priority)
802.11 uses DCF (Distributed Coordination Function) scheme of the CSMA/CA
(Carrier Sense Multiple Access / Collision Avoidance) protocol to reduce the chances
of packets collision while one more devices access the wireless media at the same
time. A client wishing to transmit has to first listen to the channel for a predetermined
amount of time so as to check for any activity on the channel. If the channel is sensed
"idle", then the client is permitted to transmit. If the channel is sensed as "busy", the
station has to defer its transmission. The random interval provides a fair transmission
chance for all the devices.
When each priority queue waits for sending packets, it has to wait a fixed time AIFSN
and a random time CW. They define time values by multiple time slots. For 802.11b,
its time slot is 20ms. The time slot of 802.11a and 802.11g is 9 ms. CW insures the
random delay time of DCF, so that the packets collision among the devices with the
same access category can be avoided. If collision occurs, CW is doubled until it
exceeds its maximum value. After every successful transmission, CW returns to the
minimum value.
The priority queue that succeeds in the competition of sending packets will acquire
Txop time to send packets. If the txop value is 0, it is limited to be a MSDC (MAC
Service Data Unit).
- Set WMM Parameters
Click the WMM Configuration button on the Advanced Wireless Settings page, the
following page appears.
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