I'm sure a lot of AP or WiFi modem/router can perform an autoscan to select the best channel to be used during the boot.
Is the channel selection also performed in other situations (other than device boot)?
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2 Answers
This is not a general truth, but some WiFi Routers/ AP's do change the channel without rebooting. Some reasons include, but not limit to:
- Noisy environment on specific channel
- Lots of other AP's on the same channel
- Interference with Bluetooth and/or other RF Communication
- Intrusion Prevention/Detection Systems trigger such as routers sensing that the WPS PIN is being bruteforced by Reaver or other tools
- Another AP with the same ESSID (name) on that channel
Please note that this behavior is very manufacturer specific / firmware specific, for example some Open Source Firmware such as OpenWRT or DD-WRT can be configured to hop channels based on user defined conditions
If your AP want to use a 5 GHz channel which is also used by radars, it NEED to support Dynamic Frequency Selection (DFS for short).
In that case, it may perform a survey on the target 5 GHz channel to check the presence of radar pulses, then may start using it, while still checking for radars.
If a radar pulse is detected after the AP has started, it sends a Channel Switch Announcement telling the stations that the AP will change channel after the next X beacons. The stations must obey or they will be disconnected.
Of course, the channel switch mechanism may also be used for other purpose than to switch away from a radar channel.
