How ios’s Wi-fi Assist works
A bad Wi-fi connection can still cause your iphone (or ipad) to use cellular data.
Added in IOS 9, Wi-fi Assist recognizes when you’re connected to a Wi-fi network, but have a poor or erratic signal. When this happens, Wi-fi Assist kicks over automatically to cellular for foreground apps to keep data flowing.
This feature is enabled by default.
Wi-fi Assist automatically excludes third-party audio and video streaming, and doesn’t relay data from apps working in the background. Nonetheless, some users wound up with surprising cellular bills ( go. macworld.com/b1ll) when they thought
they were on Wi-fi networks—it turned out Wi-fi Assist used cellular data because the Wi-fi connections were marginal. (U.S. carriers have largely switched to a fixed or flexible monthly maximum after which your cellular data rate is throttled to a very slow speed, so surprise bills are less likely.)
WHEN A WI-FI NETWORK FAILS
But Apple also may quietly switch your IOS device to cellular data in another circumstance when you think you’re connected to Wi-fi: when the Wi-fi network’s broadband connection fails, and there’s no internet link.
IOS can tell if there’s no active internet connection via Wi-fi, which is distinctly different than an active connection but poor Wi-fi reception. At least one reader has encountered this problem with a problematic ISP, which regularly drops their broadband connection, and their family’s iphones switch to cellular data, even though they all have Wi-fi Assist. Unlike with Wi-fi Assist, which limits data usage, this “no internet over Wi-fi” scenario appears to use all your cellular settings for system activities and apps. (You can modify how apps and IOS use cellular data in Settings → Cellular, then swipe down for apps and System Services.)
If you’re not sure whether you’re consuming data in this way, you can use Settings → Cellular to view current usage.
The only way to avoid using cellular data in this circumstance is to open Settings → Cellular and disable the Cellular Data switch whenever you’re on such a network. This means you won’t have internet access when the broadband connection isn’t working, but it also means you won’t consume cellular data unexpectedly. ■
IOS can tell if there’s no active internet connection via Wi-fi, which is distinctly different than an active connection but poor Wi-fi reception.