| From: James Knott via talk <talk@gtalug.org> | On 08/01/2016 05:27 PM, D. Hugh Redelmeier via talk wrote: | > So the original problem remains: how can TP-Link prevent existing | > hardware from generating too strong signals if it cannot control the | > firmware? | | The limits might be hard coded elsewhere. No, they are not. That's the problem: 1) FCC has made a new rule that manufacturers are to prevent customers from breaking the signal strength limitations. 2) current and past hardware is "dumb" and depends on software to do correct configuration (sensible from an engineering standpoint) Bonus complexity: the power limits and channel frequencies depend on the country you are currently in. If the device has to enforce this then it needs to know the country and probably not trust the user to get it right. Second best: sell a different model in each country. Alternative solutions: a) customers must not be allowed to replace the software (pretty easy and cheap; works on existing hardware) b) new hardware with "smart" radios that know not to accept violating parameters (this requires a new generation of devices, ones that are more complicated and likely more expensive; probably one device per jurisdiction). c) some kind of sandboxing of user-supplied firmware. This seems to be mentioned in the article. This is probably the most complicated solution. It would probably increase the engineering and manufacturing cost, all for a small minority of customers. And it actually limits the reach of the third party firmware in unintended ways. z) ignore the FCC. Only (a) can be retrofitted on existing hardware. TP-Link did the obvious thing. I hate it (as a customer who actually bought one of their devices to run OpenWRT). But it really is a choice between (a) and (z) on existing devices. TP-Link seems to be the first manufacturer to stop doing (z). The FCC's reaction seems to suggest that they really didn't think through what their rule meant. They really ought to clarify it. Perhaps they think that users shouldn't easily be able to violate the signal strength standards, but that flashing firmware isn't "easy". ===================== The same problem exists in the cellphone world. It used to be that there was a "baseband processor" which was kind of the gatekeeper to the radio. Android or whatever lived on another processor. They communicated with AT commands, just like a Hayes modem! But at least some systems have eliminated the baseband processor.