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Use fix 5GHz RF channels for AP7131 Wing 5.4


Dear,
I'm using three Wifi AP7131 for a wifi load balancing application.
I use the 5GHz band and want to use a fixed channel for each one :
- 100
- 108
- 116
I disabled the DFS (Dynamic Frequency Selection), and disabled the Smart RF.
When i apply this configuration, at startup the radio on each AP are in "Radar scan" state, and they get anothers channels, like 36, 48 etc.
Is it possible to force theses RF to the mentionned channels ?
Thank

9 replies

Userlevel 4
Hi,

It sounds like your operating the radios in an area where there is 5GHz radar or satellite being detected. In which case DFS (dynamic frequency selection) will move the radios onto a channel that does not fall under the DFS requirements (channels 36, 40, 44 or 48) as per the 802.11h standard.

I would suggest at looking for an alternative channel plan should these radar/satellite detection occur on a regular basis.

Hope this helps,

- Sam
Userlevel 4
Do you use the AP indoor or outdoor? In what country you try to use it.

If you hit a radar (for this channels very unusual), you can see it in the event-history.

I'll also suggest to update to the latest firmware version. I know there was a lot of DFS problems with old firmware versions.
Userlevel 3
More specifically, the implementation of DFS requires that the radios go through a listening phase before enabling their transmitters to ensure there are no radar pulses present. This is called the "Radar Scan".
There is no workaround for this, as it is required by the radio frequency management authorities of the respective countries (eg: FCC is USA, IC in Canada, etc).
Thank you for replies,
I'm in France, using AP indoor.
I thought it was possible to disable DFS.
I didn't found any upgrade firmware on this hardware.
Userlevel 2
Channels 100, 108 and 116 are DFS channels. So, it sounds like you need to use non-dfs channels which are 36-48 and 149-161. Change to one of those channels and you won't get the "radar scanning" message anymore.
Userlevel 5
Hi, Stephane.

There is one nice article to explain how to create 5Ghz Wi-Fi channel plan.

https://gtacknowledge.extremenetworks.com/articles/How_To/How-to-create-a-5GHz-WiFi-Channel-Plan/

Best regards,
Userlevel 4
France is ETSI.

You can use indoor channel 36-48 without DFS and channel 52-64 and 100-140 with DFS.

If you use a DFS channel, the radio go online with RADAR SCAN for 1 minute (120-128 5 min). If the AP see no primary sender, it start working on the DFS channel. If it see a RADAR you get a log event and the AP check a other channel.
Userlevel 3
The main issue with DFS channels is that if the AP detects a radar signal at any point in time, it must immediately get off the channel. This triggers the radar-scan for 1 minute before a different channel is selected. You cannot reliably service clients on only DFS channels, you need some non-DFS channels present in your infrastructure.
Furthermore, some radar signals can be fairly wide-band and hit several adjacent channels at the same time, knocking them all off.
False positive detections is another matter to consider when working with DFS channels.

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