DFS: Meaning of Fractional PRI in wireless context

[ANDREAS LIEBE]

Currently I look a DFS and noticed a lot of messages like this

Aug 9 05:43:01 aps307c kernel: [*08/09/2019 05:43:01.5923] dfs_confirm_radar: Rejecting Radar since Fractional PRI detected: searchpri=272, threshold=6, fractional PRI=136, Fractional PRI score=10

Can you help me to understand the meaning of "Fractional PRI" in this context?

I assume the syslog message means that the AP detected some non-WiFi signal but decided not to classify it as a radar signal. If this is true it should be save to ignore this message. Is this correct?

Thanks

Andreas

[patoberli]

You could be hitting this bug: https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvc08052/?rfs=iqvred
Which version of software are you running?

[ANDREAS LIEBE]

Thanks for your reply. I see the messages both with 8.5.140.0 (5520) and with 16.12.1 (Cat9800).

Basically I want to learn about the technical meaning of the term "fractional PRI"

[patoberli · Accepted solution]

I don't think this is publically documented. I think it's the inner functions of DFS.

While searching for it, I found this document: https://dl.khadas.com/test/github/hardware/wifi/qualcomm/drivers/qca6174/AIO/drivers/qcacld-new/CORE/SERVICES/DFS/src/dfs_process_radarevent.c which probably is the same code as Cisco uses/used.

[ANDREAS LIEBE]

Thank you, you're absolutely right. This was the information I was looking for!