Alvarion BreezeACCESS SU-A-EZ, Product Manual

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Chapter 4 - Web-managed Configuration Wireless Settings
BreezeACCESS SU-A-EZ 52 Product Manual
time the unit tries to transmit and a collision occurs; the maximum number C
used for the random number selection will be increased to the next available
value.
The Minimum Contention Window parameter is the initial maximal value C used
in the back-off algorithm. The higher the number of SUs served by the same AU,
the higher the Minimum Contention Window for each SU should be.
The available values are 7, 15, 31, 63, 127, 255, 511 and 1023. The default value
is 15.
Max Contention Window – The Maximum Contention Window parameter defines
the upper limit for the maximum number C used in the back-off algorithm as
described in Minimum Contention Window above.
The available values are 7, 15, 31, 63, 127, 255, 511 and 1023. The default value
is 1023.
AIFS – The time interval between two consecutive frame transmissions is called
Inter-Frame Spacing (IFS). This is the time during which the unit determines
whether the medium is idle by using the carrier sense mechanism. The IFS varies
depending on the type of the next frame to be transmitted, as follows:

SIFS (Short Inter-Frame Spacing) is used for certain frames that should be
transmitted immediately, such as ACK and CTS frames. The value of SIFS is
16 microseconds.

DIFS (Distributed coordination function Inter-Frame Spacing) is typically used
for other frame types when the medium is free. If the unit decides that the
medium is not free, it will defer transmission by DIFS plus a number of time
slots as determined by the Contention Window back-off algorithm (see the Min
Contention Window and Max Contention Window descriptions above) after
reaching a decision that the medium has become free.
The Arbitration Inter-Frame Spacing (AIFS) is the difference between DIFS and
SIFS. It is used to define the DIFS based on the SIFS using the following formula:
DIFS = SIFS + AIFS. It can be configured to a value between 1 and 50 time slots. A
unit with a lower AIFS has an advantage over units with higher AIFS values, since
it has a better chance to gain access to limited wireless link resources.
NOTE
A value of 0 means that the contention window algorithm is not used and that the unit will attempt to
access the medium immediately after a time interval equal to DIFS. It should only be used in
point-to-point applications