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DTUS065 rev A.7 – June 27, 2014
A: Initialization = a few ms
B: Channel scan = 56ms
C: Padding = configurable by steps of 250ms
R: Breathe time = 200ms
The ‘R’ delay is removed in reactive (foreground) scan cycles, thus shortening them while
the client is not connected to an AP.
NOTE: the ‘B’ delay is configurable in versions 2.4.3 and later. See next section.
Scanning itself normally takes place unconditionally. To gain extra
throughput when the signal level is good, you can configure a “scan
threshold”. This parameter sets the signal level above which you estimate
that no roaming is ever necessary. Setting the “scan threshold” to zero
disables this feature (default).
When set, the scan threshold is compared to the power received from the
current AP. When the power is greater than the threshold, the scan process is
interrupted at the next scan period. When the power received is lower than
the threshold, the scan process is restarted.
To avoid oscillation effects due to a received power rapidly changing around
the threshold, a hysteresis is implemented. Its value is the same as the
hysteresis used for the “leave threshold”.
NOTE: the scan threshold is configurable in versions 2.2.7 and later.
Scanning
enforced
Scanning
enforced
time
Radio
signal
Scanning disabled
Threshold
Hysteresis
(configurable)
Leave
threshold
Current AP signal level
Scan
threshold
(configu-
rable)
roaming
takes place
scanning
restarts
scanning
stops