Say you didn’t pay your internet bill or your internet connection is interrupted due to a fault with your service provider. As far as your phone or computer is concerned, your wireless router is perfectly functional and will remain connected despite not having an internet connection. With WiFi Assist, iOS 9 will attempt to automatically switch between WiFi and cellular data depending on the situation.
So like in the example above if iOS 9 detects that your WiFi connection is weak or if its performance falls below a certain threshold, it will then automatically swap to cellular. Prior to this, users would have to disable WiFi manually, which while it isn’t that big of a deal, sometimes you might forget to turn it back on.
The feature will also better indicate when WiFi Assist is active as the WiFi icon will now turn grey before one of the symbols for cellular data is shown. Unfortunately there is still no word on when iOS 9 will be officially released, but chances are we will learn more come next month when Apple is expected to announce their new iPhones.