Apple introduced Continuity as a way to bind together various features across the two kinds of systems. It’s great when it works, and it’s clearly gotten better. AirDrop only fails on me sometimes instead of mostly, for example. Continuity includes Instant Hotspot, Universal Clipboard, and other features.
But Macworld reader Tom is having trouble with the Cellular Calls part of Continuity, which effectively extends an iPhone voice calling service to work with any associated Mac or iOS device. He has both Wi-Fi and ethernet active on his Mac laptop when he’s using it at home, and phone calls ring on his Mac through Continuity. However, if he has both ethernet and Wi-Fi active, he can never answer the call: FaceTime reports the call has failed. Disable one networking method, and it works.
Apple’s Continuity setup instructions note that you need to use either ethernet or Wi-Fi for cell calls, but doesn’t say anything about both. My suspicion is that the protocol doesn’t distinguish between two different routes to reach the same destination, resulting in a jumble. (This limitation is likely artificial, as the technology could pick one address or the other on the local network, but it’s clearly not implemented for "multi-homed" situations like this.)
Tom prefers to use ethernet, because the connection is ostensibly faster and more stable than the Wi-Fi one. But he uses his Apple Watch to unlock his Mac (another Continuity feature) and that works only over Wi-Fi. Thus, he’ll have to pick just Wi-Fi if he wants both Auto Unlock and receiving voice calls on his Mac.
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