I may well not understand the purpose of Wi-Fi Assist in the Cellular Settings on the iPhone so…
If I/we are in a situation where either our LAN is down or more likely Comcast is down, our iPhones do not switch to cellular.
When we turn Wifi Off then all is good and we can proceed with whatever using cellular but then one or both of us will forget to switch back when Comcast is back up.
Shouldn’t Wifi Assist do this automatically… That is switch the iPhone to cellular if it is not getting a good local network or internet connection over Wifi?
According to the Apple web page on Wi-Fi Assist your phone should start using data over cellular when your Wi-Fi signal is poor if you have Wi-Fi Assist enabled. It doesn’t say anything about it automatically switching back to Wi-Fi automatically, but one would assume that it should. Note that there are a few situations where Wi-Fi Assist won’t kick in listed at the bottom of that web page. Sometimes iPhone strange behavior can be resolved by restarting your phone. You might also check your phone’s setting for Cellular to be sure the apps you are using are allowed to use cellular data. That may override your preference to use cellular when Wi-Fi is not available via Wi-Fi Assist.
My guess is the wifi throughput between your iPhone and your access point is still perfectly fine even when Comcast service to your AP goes down. My understanding is Wi-Fi Assist will switch you over to cellular when the connection to the AP is bad. But in your case that connection is fine, the problem is further upstream.
You’d think though that it should be easy for iOS to discover there’s no working upstream connection on the AP—in fact Apple’s AirPort Utility will report exactly that when it’s an AirPort base station that loses its WAN connection. But considering your report, my guess is that’s not happening here. Perhaps because indeed that’s not part of Wi-Fi Assist’s functionality. Unfortunately, Apple doesn’t clarify that point in the KB article.
I’m wondering if it’s the word “switch” that is confusing. Apple uses that word in the support doc linked in this thread, but I’m wondering if to you it means that the toggle in Settings > Wi-Fi should visibly switch back and forth between the on and off states? If that is what you’re expecting, I don’t believe that’s what Wi-Fi Assist will actually do. My interpretation is that the “switch” is happening internally, and that the toggle remains in the Wi-Fi on position. Just a hunch; correct me if I’m wrong.
I think you’re correct. It’s not that the wi-fi toggle will actually switch to the off position. It remains on which also makes sense because if connection between the iPhone and the AP is restored, you’ll be back to using wifi.
When Wi-Fi Switching activates because of poor wifi connection, as Apple plus it, “you’ll see the cellular data icon in the status bar on your device.” The switching in that sense is indeed internal — you won’t see any UI toggles in Settings change.