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The back-off timing for each access category consists of a fixed period called the Arbitrary
Inter-Frame Space Number followed by a random period called the Contention Window
(CW), both specified in multiples of the slot time.
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WMM (Wireless Multimedia) Transmission Opportunity: defined by IEEE 802.11e, the
TXOP is the interval of time when a particular STA (station) has the right to initiate
transmissions.
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Advertised in the EDCA parameter set element to indicate that the admission control is
taken over by the client when it is turned on. It only has the effect on AC VI and VO.
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Theses values of AIFS, CWmin, and CWmax are announced by the AP via beacon
frames.The AP can adapt these parameters dynamically depending on the network
conditions. Basically, the smaller AIFS and CWmin, the shorter the channel access delay
for the corresponding priority, and hence the more capacity share for a given traffic
condition.However, the probability of collisions increases when operating with smaller
CWmin. Theses parameters can be used in order to differentiate the channel access among
different priority traffic.
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You may slightly adjust these values when you experience latency in your
network traffic according to the following explained properties for each of the data
types. For instance, if you experience delay in your video applications, you may give a
bigger value for TXOPLimit while reduce the difference between CWmin and
CWmax, and the number for AIFSN.
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Each station maintains a Contention Window (CW), which is used to select the random
back off counter. The BC is determined as a random integer drawn from a uniform
distribution over the interval (0, CW).The CW size is initially assigned CWmin, and
increases when a transmission fails, i.e., the transmitted data frame has not been
acknowledged.After any unsuccessful transmission attempt, another back off timer is
performed, with an upper bound of CWmax.This reduces the collision probability in case
there are multiple stations attempting to access the channel.
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should be smaller for delay-sensitive data
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should be smaller for delay-sensitive data
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should be smaller for delay-sensitive data
