This is one of the better features found in iOS 9. When enabled, Wi-Fi Assist switches to a cellular connection when you're connected to a weak Wi-Fi signal. This is useful when you're away from home or work and are using a public Wi-Fi connection or provider hotspot. Your device will switch to a stronger cellular signal when your Wi-Fi dips below one bar or is not responding. You can enable Wi-Fi Assist on your iPod touch, iPhone or iPad by navigating to Settings > Cellular and scrolling all the way down until you see the Wi-Fi Assist slider.
What does Wi-Fi Assist do on my iPad?
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