User Manual

BROWAN COMMUNICATIONS Page 92
indicate the admission control is required for each
of the ACs.
Access Point
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.
STA
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