I actually watched a session that talked about this very briefly. Apparently what happens is when you are on the fringe of your wifi (meaning it still shows your connected, but in an extremely weak state), he wifi icon will go gray and then switch over to cellular. It works quite well, and I have actually seen an improvement. So when your wifi icon shows you have one (1) bar, but it is not responding, it will just switch over to cellular. I hope this helps.
Which session did you watch that covered Wi-Fi Assist? Was it located in the WWDC Videos, and if so do you recall which video it was in? If you happen to remember which one it was in, I'd love to know.
You're very unlikely to find any information on the threshold value (whether that's RSSI or milliseconds of lost connection etc.) that triggers the switch because Apple have no history of publishing technical specifications of the inner workings of its OSs.
It's expected to "just work" and, if it doesn't, there are various feedback channels in place.
Hi all, thank you for responses.
We create Apps that communicate with hosts on "local area network".
So if iPhone suddenly switches to cellular network, our Apps can't work.
I'm afraid that some users may use it in environment RSSI is not so good, and may experience switching to cellular network although it works on older version iOS.
For that reason, we may have to announce "use our apps at <suitable> environment" to users, but I have no idea about what is <suitable> environment...
Does anyone have updates?
It seems that there are no documents in iOS Developer Library yet.