While I was performing WiFi client troubleshooting, I captured the following Cisco WCS events about radar detection :
In the above figure, two APs selected a different channel because they detected a radar using the same frequency on the 5 GHz band. The Cisco UWN Solution complies with regulations that require radio devices to use Dynamic Frequency Selection (DFS) to detect radar signals and avoid interfering with them.
Using DFS, a Cisco controller monitors operating frequencies for radar signals. If it detects radar signals on a channel, the controller takes these steps:
- It changes the access point channel to a channel that has not shown radar activity within the last 30 minutes. (The radar event is cleared after 30 minutes.) The controller selects the channel at random
- If the channel selected is one of the channels in Table-A,itscans the new channel for radar signals for 60 seconds. If there are no radar signals on the new channel, the controller accepts client associations.
- It records the channel that showed radar activity as a radar channel and prevents activity on that channel for 30 minutes
- It generates a trap to alert the network manager (in this case, WCS)
Table A - DFS-Enabled 5-GHz Channels
DFS (dynamic frequency selection) is published as part of IEEE Std. 802.11h amendment.
If you wish to know more about DFS and other WiFi topics, I encourage you to read CWNA Certified Wireless Network Administrator.
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