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Appendix A:
Dynamic Frequency Selection
The following section details notes and questions concerning the 2.4 / 5.4 GHz MOTOMESH Duo and
dynamic frequency selection in the presence or radar triggers and interference. First it is important to
detail the auto channel selection feature and the specific behaviors with respect to radar and interference
will be discussed.
Auto-Channel Selection
Auto-channel selection is a feature that attempts to choose the best operating channel for one of the
transceivers in a Duo access point at the time it is initiated. Auto-channel selection can be enabled /
disabled independently on both the 2.4 GHz and 5.4 GHz transceivers in the Duo product.
Preferred Channel List
Each access point has a list of preferred channels that are configured by the operator. The list contains all
of the channels that a Duo device is allowed to operate in for a given transceiver. There is a separate
preferred channels list for the 2.4 GHz and the 5.4 GHz transceiver. When a scan is performed only the
channels in this preferred channel list are considered.
Scan Triggers
An auto channel selection scan is triggered by five stimuli:
1. Reboot – Upon reboot the Duo transceivers will auto channel select on each of the transceiver
that it is enabled on.
2. Very high route metric – The Duo node will automatically establish a route to the best IAP in its
current operating channel. This IAP route is selected based on the lowest routing metric to an IAP
and is constantly updated. If adverse channel conditions are encountered the route metric will
become higher than channels that are not impaired. If the auto-channel selection feature is
enabled, and the current best IAP has a route exceeding a high threshold for 10 minutes then the
device will initiate an auto channel scan to find an operating channel where a route to new route
to an IAP can be established with a lower (better) route metric. If the result of the scan indicates
that the original channel is still the best operating channel, the Duo will return to the original
channel.
3. Extremely high noise floor – When a noise floor is detected that would prohibit successful
communication with other devices the Duo will reboot and initiate the channel scan detailed in 1.
4. DFS radar detection – When radar is detected and the auto-channel scan is enabled, the radar
detection will trigger and auto-channel scan.
5. One Point Wireless Manager has the ability to initiate a channel rescan, either as a periodically
scheduled or one-time event.
The Scan
Once a scan is triggered on a transceiver that has auto-channel scan enabled the Duo will switch to the
next channel in the preferred channel list and listen passively for a few hundred milliseconds. While it is
listening, it records all of the beacons that are present in the channel. Duo then moves to the next
channel in the list until all of the channels have been sampled. If the trigger that caused the scan was a
DFS trigger that channel is marked unavailable for 30 minutes and it is not scanned. Once the scan is
complete an algorithm inspects the list of beacons in all of the available channels and picks a channel
that has the best route metric and channel conditions to an IAP. It then retunes to that channel. Under
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