[raarts]

> In practice not likely.

Depends. It apparently is real enough. Higher 5GHz WiFi band channels can interfere with airport radar. That's why the standard mandates a router to switch to another channel if it detects radar signals.[1]

But of course using an illegal channel is simply illegal...

[1] http://wifi-insider.com/wlan/dfs.htm

[swiley]

The rules for using DFS 5ghz channels are so harsh that the networks built with them are almost uselessly unreliable. You're /far/ better off just not using channels requiring DFS. Especially if it means you can actually own the equipment you paid for.

[yuhong]

Which also reminds me of LTE-U vs WiFi. I wonder if the fundamental problems are similar.

[pdabbadabba]

I cannot imagine why you're being down-voted. This isn't hypothetical; the FCC imposed these security restrictions after reports of actual interference to airport weather RADARs.

https://www.fcc.gov/general/u-nii-and-tdwr-interference-enfo...

[wtallis]

Note however that it appears that virtually all of those instances of interference were tracked down to Ubiquity point to point link devices. TP-Link's ordinary consumer access points and routers may have been out of compliance with the letter of the law, but they weren't causing actual harm to airport operations, let alone enough harm to justify banning OpenWRT.

[Sanddancer]

One individual home router operating illegally won't do much to increase the noise floor, but each router operating illegally adds that much more to the background noise and makes it that much more difficult for the weather radar to function properly. So yes, they were doing harm to airport operations. It's just like light pollution -- one light won't block out the stars, but a million will.

[wtallis]

Do you have specific knowledge that diffuse ground-based access points impair the narrow beam TDWRs at issue, or are you just making a broad generalization? It's a decent analogy, but I can think of quite a few differences between a short range weather radar and a radiotelescope.

[Sanddancer]

It was one of the things discussed when making the decision to allow restricted use of the frequencies. Also, keep in mind that more than just airport weather radar use the frequency range in question. That frequency range is also used for satellite uplinks and downlinks. There was a lot of research put into the FCC's decision before it was enacted.

https://www.ntia.doc.gov/files/ntia/publications/ntia_5_ghz_...

https://apps.fcc.gov/edocs_public/attachmatch/FCC-14-30A1.pd...

[wtallis]

Those are informative but rather long documents. Are there any specific portions you'd like to call my attention to? Because I'm seeing statements like "There have not been any cases of TDWR interference identified for other unlicensed device applications" (referring to things other than outdoor point to point links), and the sole satellite communications provider operating in the U-NII-1 band being concerned only with limiting the power radiated upwards from outdoor access points and unconcerned with indoor access points.

For such a well-studied topic and with such strong regulation on the table, there really ought to be something relevant and approaching a smoking gun to point to.

[yuhong]

And how many home users in practice even modify the firmware in the first place.

[pdabbadabba]

They were causing interference because they could be (and were) modified to behave in a way that violated FCC regulations. So the FCC made another regulation that said devices should not be modifiable in that way. This seems totally sensible to me. TP-Link violated this rule--not just the "letter" of it.

Also, nobody has banned OpenWRT. If you read the consent decree, you'll see quite the opposite.

[wtallis]

> "Also, nobody has banned OpenWRT. If you read the consent decree, you'll see quite the opposite."

The FCC's initial knee-jerk reaction was very much along the lines of banning OpenWRT, and TP-Link subsequently deployed firmware to make it harder to put OpenWRT on their routers. Sure, they're now saying that it wasn't their intention and that they'll try to find a way to avoid it, but banning OpenWRT was and still is on the table and TP-Link and others have taken steps down that road.

As for the FCC rules: they still haven't put forth a clear explanation of how easy or hard the modifications have to be to get a router vendor in trouble. TP-Link's routers are still not fully secured, and just about everybody else still has routers on the market that are no more secure against modification than the TP-Link products. Absent any evidence of actual interference being traced to TP-Link products, it doesn't look like the FCC is merely being strict about enforcing their rules—it's more like they're making an example of TP-Link but deliberately withholding from a broader enforcement campaign while they and the industry try to figure out what to do (ie. can currently deployed hardware be made secure enough without locking it out of third-party firmware?). Meanwhile, the FCC is still having a chilling effect on open-source wireless router software and they still haven't provided any strong evidence that the harm is justified.

[pdabbadabba]

This seems like a long way of saying: "correct, nobody has banned OpenWRT, but the new FCC rules have made it riskier for manufacturers to support things like OpenWRT in the future."

To which I would mostly agree, with an important caveat: TP-Link's violation actually had nothing to do with allowing third-party software like OpenWRT. Its own UI allowed end users to change region settings. This seems clearly problematic under the Commission's rules, even if the rules are vague in other respects.

So, on balance, I think this order sends an important signal that very well may be able to support things like OpenWRT without getting into trouble. But you're right that we don't know that for sure, given the language of the decree. All we know is that the FCC would really like it if the industry could figure out how to support OpenWRT, etc. without simultaneously making it easy to circumvent FCC rules.

[wtallis]

> This seems like a long way of saying: "correct, nobody has banned OpenWRT, but the new FCC rules have made it riskier for manufacturers to support things like OpenWRT in the future."

Nope. TP-Link has locked out OpenWRT. It's not a highly effective lock, but it is real and they actually deployed it as an update for existing hardware in the field and for new sales. They're not going to revert to the way things were and instead are trying to develop a new security strategy that clearly won't be feasible on the existing hardware that is now locked out.

And it's not like any router vendor ever actually actively supported third-party firmware; it's just a matter of how much DRM they use to interfere with it.