What does DFS Timeout

  • 3 April 2014
  • 3 replies

What does DFS Timeout mean in the 5.0 gig freq range of aps.

3 replies

Userlevel 4
DFS in the 5GHz spectrum refers to specific bands/channels that must co-exist with weather, police, and other radar applications. If an AP is using a DFS channel and it detects a radar signal in the channel the AP must change channels within microseconds and cannot go back to that channel for a minimum predetermined amount of time. The minimum cannot be lowered because it is predicated by regulations specific to the country the AP is in, but I suspect you can increase the time whereby the AP will not attempt to use the channel where radar signals were originally detected. As a best practice, in the 11abgn days DFS channels were not commonly used in deployments because most clients did not support DFS channels. However, with the advent of 11ac, the 5G will come under a spectrum crunch when you start using 80 MHz and eventually 160 MHz channels. We have heard (but have not confirmed) that many of the new 11ac clients support DFS channels, so it is possible that with 11ac the use of DFS channels will become more widespread. But keep in mind that if you use DFS channels in your deployment, you still need to service legacy 11an clients which most likely will not support DFS channels. So if you do decide to use DFS channels in your RF plan make sure that you have enough overlap with non-DFS channels in the same coverage area to provide connectivity to 11an clients.


Thanks for the detailed info. 5 years later 🙂 as you know most clients do support and use DFS channels, I am downtown and in a building so any extra channel helps 


My question is when a DFS timeout occurs, what is the impact on the client connected to that ap? Is it a transparent? Do they disconnect and reconnect? If I don't have enough non DFS coverage because I know all our clients support DFS, should I worry about client connetivity impact during a timeout?



Userlevel 7

If a DFS event is triggered the client will drop to hopefully another access point while the ap goes into a scan state looking for an unoccupied channel.