Alvarion BreezeACCESS VL 5.4 System Manual page 115

Operation and Administration
For SU-A-24 VL the available rates are 6, 9, 12, 18 and 24 Mbps, and the
default is 24 Mbps.
Number of HW Retries
The Number of HW Retries parameter defines the maximum number of
times that an unacknowledged packet is retransmitted. When the Multi
Rate Support algorithm is disabled, or when the Multi Rate Support
algorithm is enabled but the Software retry Support is disabled, a frame
will be dropped when the number of unsuccessful retransmissions reaches
this value. For details on the effect of this parameter when both the Multi
Rate Support algorithm and the Software Retry Support feature are
enabled, refer to Multi-Rate on page 5-55.
The available values range from 0, which means no retransmissions to 10.
The default value is 4.
Multi-Rate
The Multi Rate algorithm enables to adapt the transmission rate to the
prevailing conditions of the applicable radio link. The algorithm provides
Access Units with simultaneous, adaptive support for multiple Subscriber
Units at different rates, as transmission rate decisions are made separately
for each associated SU.
Link quality fluctuates due to various environmental conditions.
Dynamically switching between the possible transmission rates increases
the probability of using the maximum rate suitable for the current radio
link quality at any given moment.
The decisions made by the Multi Rate algorithm relate to the transmission
rate for new frames (first trial attempt) as well as the rate for
retransmissions. The decisions are based on multiple parameters,
including the RSSI of received acknowledgements from the relevant unit,
the time that has passed since last transmission to the relevant unit, and
the recent history of successful and unsuccessful
transmissions/retransmissions. In the AU the decision algorithm is
performed separately for each SU.
The transmission/retransmission mechanism operates as follows:
a. Each new frame (first transmission attempt) will be transmitted at
a rate selected by the Multi Rate algorithm.
5-55