AirLive AirMax5N-ESD - Manual (Page 45)

4. Web Management-Wireless and WAN Settings
AirLive AirMax5N/ESD User’s Manual
39
CWmin and CWmax
If an access point detects that the medium is in use, it uses the DCF random backoff
timer to determine the amount of time to wait before attempting to access a given
channel again. Each access point waits some random period of time between retries.
The wait time (initially a random value within a range specified as the Minimum
Contention Window increases exponentially up to a specified limit Maximum
Contention Window.
The random delay avoids most of the collisions that would occur if multiple APs got
access to the medium at the same time and tried to transmit data simultaneously. The
more active users you have on a network, the more significant the performance gains
of the backoff timer will be in reducing the number of collisions and retransmissions.
The random backoff used by the access point is a configurable parameter. To describe
the random delay, a "Minimum Contention Window" (CWMin) and a "Maximum
Contention Window" (CWMax) is defined.
CWmin: The value specified for the Minimum Contention Window is the upper
limit of a range for the initial random backoff wait time. The number used in the
random backoff is initially a random number between 0 and the number defined
for the Minimum Contention Window.
CWmax: If the first random backoff time ends before successful transmission of
the data frame, the access point increments a retry counter, and doubles the
value of the random backoff window. The value specified in the Maximum
Contention Window is the upper limit for this doubling of the random backoff.
This doubling continues until either the data frame is sent or the Maximum
Contention Window size is reached.