DFS is a mechanism to allow unlicensed devices to use the 5 GHz frequency bands already allocated to radar systems without causing interference to those radars. The concept of DFS is to have the unlicensed device detect the presence of a radar system on the channel they are using and, if the level of the radar is above a certain threshold, vacate that channel and select an alternate channel.
In a default configuration, 13 of the available 22 (20 MHz) 5 GHz channels in the US are subject to Dynamic Frequency Selection (DFS) rules. The Aruba controller will not select the DFS channels as "allowed" for ARM to assign to the APs due to the concerns of interference from satellite and radar transmissions, if you select 5 GHz, the DFS channels will not be used until you enable them. You can see this by looking at the regulatory domain profile in use on the controller for that region ad checking the allowed channels.
Note:- One must be careful when attempting to use these channels to ensure they either know they will not be impacted by radar and/or know the side effects if you do. When enabling DFS channels the APs will perform off-channel scanning to detect the presence of satellite and radar transmissions, and switch to a different channel if it detects that satellite or radar transmissions are present. Also Enable " Advertise 802.11d and 802.11h Capabilities " under AP Configuration>802.11a radio profile>Advanced This Enable the radio to advertise its 802.11d (Country Information) and 802.11h (TransmitPower Control) capabilities. This standard provides Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to the 802.11a This option is disabled by default.
ArubaOS 6.2 enables FCC DFS channels in the 5GHz band for the following APs: AP-92 and AP-93 AP-93H AP-105 AP-104 AP-134 and AP-135 Prior to ArubaOS 6.2, FCC DFS channels were only enabled on the AP-120 Series AP. Note:- For info on DFS support for newer AP's please refer to the corresponding AP datasheet.
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