Alvarion BreezeACCESS VL System Manual page 158

Chapter 4 - Operation and Administration
ESSID - The ESSID of the AU.
In addition to the neighboring AU data table, the following information is
displayed:
Best AU Support
Preferred AU MAC Address
Number of Scanning Attempts
Associated AU MAC Address (the MAC address of the selected AU)
4.2.6.2.7 Scanning Mode (SU only)
The Scanning Mode parameter defines whether the SU will use Passive or Active
scanning when searching for an AU.
In passive scanning, the SU "listens" to the wireless medium for approximately
two seconds at each frequency, searching for beacons. The disassociation period,
which is the time from the moment the link was lost until the SU decides that it
should start searching for another AU, is approximately seven seconds.
In some situations when there is a high probability that SUs might need to roam
among different AUs, the use of active scanning enables to significantly reduce
the link establishment time. This is achieved by using shorter dwell periods,
transmitting a Probe Request at each frequency. This reduces the time spent at
each frequency as well as the disassociation period.
When DFS Option is enabled, Scanning Mode is forced to Passive.
The default selection is Passive.
4.2.6.2.8 Power Control Parameters
The Automatic Transmit Power Control (ATPC) algorithm simplifies the
installation process and ensures optimal performance while minimizing
interference to other units. This is achieved by automatically adjusting the power
level transmitted by each SU according to the actual level at which it is received
by the AU. To support proper operation of the system with optimal performance
and minimum interference between neighboring sectors, the ATPC algorithm
should be enabled in all units.
The algorithm is controlled by the AU that calculates for each received frame the
average SNR at which it receives transmissions from the specific SU. The average
calculation takes into account the previous calculated average, thus reducing the
effect of short temporary changes in link conditions. The weight of history (the
previous value) in the formula used for calculating the average SNR is determined
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BreezeACCESS VL System Manual