Alvarion BreezeNET B System Manual page 177

Chapter 4 - Operation
DIFS equal SIFS plus AIFS, where AIFS is two time slots (in BU/RB-B14/28/100,
AIFS for low priority packets can be configured to a value higher than 2 when the
Wireless Link Prioritization feature is enabled. See
The system uses an exponential Back-off algorithm to resolve contention between
two units that want to access the wireless medium. The method requires each
unit to choose a random number N between 0 and a given number C each time it
wants to access the medium. The unit will attempt to access the medium only
after a time equal to AIFS plus N time slots, always checking if another unit has
accessed the medium before. Each 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 available values are 7, 15, 31, 63, 127,
255, 511 and 1023.
The Minimum Contention Window parameter is the first maximum number C
used in the back-off algorithm.
The available values are 0, 7, 15, 31, 63, 127, 255, 511 and 1023. 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 equal to DIFS.
The default value is 15.
4.2.6.5.3 Maximum 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.
4.2.6.5.4 Maximum Modulation Level
When the Adaptive Modulation algorithm (see
changes the modulation level dynamically according to link conditions. The
purpose is to increase the probability of using the maximum possible modulation
level at any given moment. Although the algorithm will avoid using modulation
levels that are too high for the prevailing link conditions, it might be better under
certain conditions to limit the use of higher modulation levels. If the link quality is
not sufficient, it is recommended that the maximum modulation level be
decreased, as higher modulation levels increase the error rate. In such conditions,
a higher Maximum Modulation Level increases the number or retransmissions
before the modulation level is being reduced by the Adaptive Modulation
algorithm. A high number of retransmissions reduces the overall throughput of
the link.
BreezeNET B
Section
Section
153
Menus and Parameters
4.2.6.6.3.6).
4.2.6.5.9) is enabled, it
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