Unstable DFS channel selection

[RandomRancho]

I've a Netgear R7450 AC router which slowly drifts back to channel 48 from any DFS channels I set. Once the router is on 48, it doesn't go back DFS channel. At the same time, I've an Ubiquiti access point in my house which constantly stays at either 100 or 102. I'm guessing it's the problem with the Netgear router which is not doing great job at staying on a DFS channel.

Is there any setting which can force the router to come back to DFS channel?

Thanks!!

 

[TheLostSwede]

It could be because it's an older device and as such it only moves away from the DFS channels when there's a trigger event and doesn't move back. If I remember correctly, this was an issue with some early DFS devices.

 

[RandomRancho]

It could be because it's an older device and as such it only moves away from the DFS channels when there's a trigger event and doesn't move back. If I remember correctly, this was an issue with some early DFS devices.

Bought this recently since this has wave-2 and DFS frequency. If the DFS is not functional then it's a deal breaker

Any suggestion of a decent AC/AX router which has a functioning DFS frequency?

 

[TheLostSwede]

Bought this recently since this has wave-2 and DFS frequency. If the DFS is not functional then it's a deal breaker

Any suggestion of a decent AC/AX router which has a functioning DFS frequency?

Wave 2 doesn't mean DFS was properly implemented though. I have an R7800 and it didn't ship with DFS support and a lot of other features have been added over time.

It's also a "cheaper" Netgear router based on a Mediatek platform, which they don't use in a lot of their products.
I don't want to pick on Mediatek as such, but I used to work for a router manufacturer that made Mediatek based products and they are sloppy sometimes. We had an issue that it took us two months to find the source of, which was related to their Wi-Fi driver. It took them three months to fix it after we reported it and only after multiple calls and meetings.

I'm not saying it's the case here, as Netgear has also had some weird DFS related issues if you search their forums. It doesn't help that your router is a shop specific SKU. That said, have you updated to the latest firmware?

 

[ColinTaylor]

I'm guessing it's the problem with the Netgear router which is not doing great job at staying on a DFS channel.

Not necessarily. It could be that it's the Ubiquiti that is at fault because it should be moving channel (because of radar) but isn't.

It could be because it's an older device and as such it only moves away from the DFS channels when there's a trigger event and doesn't move back. If I remember correctly, this was an issue with some early DFS devices.

All Asus devices I've had work this way. There's nothing in the DFS regulations that say a device should move back to a channel that previously had radar interference. Arguably you wouldn't want to this to happen.

The 5GHz “Problem” For Wi-Fi Networks: DFS

Wi-Fi networking provides us with 2 bands for the operation of wireless LAN networks: the 2.4Ghz band and the 5GHz band. The 2.4GHz band has...

wifinigel.blogspot.com

 

[TheLostSwede]

All Asus devices I've had work this way. There's nothing in the DFS regulations that say a device should move back to a channel that previously had radar interference. Arguably you wouldn't want to this to happen.

The 5GHz “Problem” For Wi-Fi Networks: DFS

Wi-Fi networking provides us with 2 bands for the operation of wireless LAN networks: the 2.4Ghz band and the 5GHz band. The 2.4GHz band has...

wifinigel.blogspot.com

Sorry, but why wouldn't you want that to happen? The idea with DFS as far as I understood it, was that there are more available channels, but if the router detects radar signals, it switches - temporarily, for a defined period of time - to a non DFS channel. Once it either detects that there is no longer any radar signals, or after the pre-defined time period, it moves back to the DFS channel.
I mean, if it didn't, the whole implementation would be pointless, as you could use the DFS channel once and then you'd be back at the default channels outside of the DFS ones and would be limited to the same issues that existed before DFS was implemented.
Edit: The non-occupancy period is apparently 30 minutes at a minimum and after that the router should switch back to the previous DFS channel. It even says as much in your link.

Non-Occupancy Period​

Once radar has been detected on a channel, then the “Non-Occupancy Period” begins. This is a 30-minute period in which no further transmissions will be made by the AP on the affected channel.
At the end of the 30-minute period, most APs will attempt to return to their original channel, subject to a channel availability check. (Again behaviour in this area varies between vendors)

 

[ColinTaylor]

I did say "arguably". In other words a case can be made for either behaviour. I'm not saying one way is right and the other is wrong.

but if the router detects radar signals, it switches - temporarily, for a defined period of time - to a non DFS channel.

It doesn't have to switch to a non-DFS channel. It can be any channel including DFS.

In some solutions, APs that detect radar will move to channel 36 exclusively. In other solutions, APs will choose to move to any of the available non-DFS channels. Some will jump to any available 5GHz channel they find (DFS or non-DFS). Behaviour in this area seems to be inconsistent and is not defined within the 802.11 standard.

Edit: The non-occupancy period is apparently 30 minutes at a minimum and after that the router should switch back to the previous DFS channel. It even says as much in your link.
:
At the end of the 30-minute period, most APs will attempt to return to their original channel, subject to a channel availability check. (Again behaviour in this area varies between vendors)

As stated, whether an AP attempts to change back is down to the vendor. There is nothing in the DFS regulations that say this should/must happen. Bear in mind that that blog post is written from the perspective of an enterprise setup where it's very desirable that APs return to their original channels. With consumer equipment it's probably more desirable that the router just finds the best channel for itself and stays there rather than constantly switching back and forth between channels.

 

[RandomRancho]

Thanks @ColinTaylor and @TheLostSwede for your input.

If router manufactures are doing what Colin mentioned, then DFS channels are mostly useless considering it's almost impossible to avoid radar signals in cities. Also, there is also false positives which even makes it more unreliable.

Are there any router manufacture who implement the version where they try to go back to DFS channel after the detection grace period?

 

[thiggins]

Using 80 MHz or, worse, 160 MHz wide channels and trying to use DFS channels is not a recipie for stable operation in many cases.

Large multi-AP networks typically use 20 or maybe 40 MHz channels at most. This provides more options for switching channels when radar is detected in DFS.

With wider channels, there are not many channels left to switch to. And trying to switch back would lead to posts like yours and probably calls/emails to the manufacturer's support team.

Consumer manufacturers usually walk a line on default settings that balances performance and minimizes the chance of support contacts.