Apple’s latest operating system contains a new function called ‘Wifi Assist’ which is switched on by default.
When the signal strength of 3G or 4G mobile data is greater than your wi-fi router signal the app automatically switches to receive mobile data instead. You think that you are connected to free wi-fi but are actually eating up your mobile data bundle. If you are on an unlimited data plan this might be acceptable as it will give you uninterrupted service when moving locations – if however you (or your staff) have a fixed data bundles then you might see mobile data use increase unexpectedly.
The app is accessed via Settings>Mobile Data>WiFi Assist.
One possible compromise is as follows – iOS9 includes the ability to control which apps have access to mobile data and which can only use wi-fi. Users can restrict non-essential data-intensive applications (such as media streaming) to wi-fi, and allow more critical functions to use mobile data as required. This option is accessed via the same Settings>Mobile Data menu.