RLX2-IHx Series ♦ 802.11a, b, g, n
Configuring a Radio - Detailed Configuration
Industrial Hotspots
User Manual
ProSoft Technology, Inc.
Page 96 of 248
Background Scan
The
B
ACKGROUND
S
CAN
parameters group are used to modify the algorithm used by an
RLX2-IHx in Repeater or a Client mode to search for parent candidates that may be on
other channels.
The list of channels to be scanned for potential Parents is obtained from the current
Parent, either from its Beacon or an explicit Neighbor Report request.
It is critical when doing a background scan that data loss be minimized or eliminated
when switching to scan a radio channel different than that of the current Parent. When
configuring these settings it is important to be cognizant of overall time the background
scan will take, as that will be added latency to data before it can be delivered after the
background scan.
Latency = Scan Delay + (Scan Dwell x Channels-per-Scan)
Therefore the following steps are taken during a background scan attempt.
1
Signal the current parent that we are about to do a background scan.
2
Wait for
Scan Delay
time to receive any data packets sent by the parent before it
was able to process our background scan signal.
3
Switch to another channel and Probe for an alternate parent that is using our SSID.
4
Wait for
Scan Dwell
time on this channel to receive any Probe Responses.
5
If the number of channels scanned is less than the
Channels/Scan
value go to step
3.
6
Otherwise once the
Channels/Scan
channels have been scanned, switch back to
the current Parent’s channel.
7
Signal the current parent that we have completed our background scan allowing it to
send any data frames it has buffered since our signal in Step 1.
Parameter
Description
Scan Threshold
Background scans will be triggered as long as the current Parent’s
RSSI is below this threshold, with units of dBm. At each
Scan Interval
the RLX2-IHx will scan the number of channels set by the
Channels/Scan
parameter before returning to the current Parent’s
channel and resuming normal operation.
A value of 0 in this parameter shall disable background scanning.
Valid threshold values range from -30 to -99 dBm. Typically this value
should be set 5 to 10 dB lower than the
Roam Threshold
parameter
so that when moving away for the current Parent, the best alternate
Parent can be found prior to having to make a roam decision.
Scan Delay
This parameter is used when the RLX2-IHx is in a Client mode and
determines the amount of time the unit will wait after having sent the
AP a signal telling the AP that the unit will be going off channel. This
delay allows some time for the AP to deliver any data frames that have
already been committed to the radio hardware for transmission.
Valid values range from 10 to 250 msec. and must be a multiple of 10.
This value should be as small as possible to minimize overall latency
introduced by each background scan attempt, but large enough so
that data is not lost each time a background scan is performed.