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A Little-Heralded New iOS 7 Feature: Multipath TCP
Olivier Bonaventure writes "Besides changes in UI, multitasking and other features that the press discusses, iOS7 also includes support for Multipath TCP. Multipath TCP is a major extension to TCP that is able to use different interfaces for the same connection. Until now, Multipath TCP has been mainly used by researchers with a modified Linux kernel. iOS7 changes that, with millions of Multipath-TCP enabled devices that can switch from 3G to WiFi without losing existing TCP connections. This is not yet the case on iOS7, which currently seems to only enable it for SIRI, but other use cases will likely appear in the future."
One of my everyday rituals is walking out of my office building and across the parking lot. During my walk across the parking lot, I ask Siri to call my wife. At some varying point, the building's Wifi cuts out and 3G kicks in. As soon as I read this headline, I knew exactly how it would apply to my life.
This would also be good for Pandora. My home's Wifi reaches almost to my street corner, so I can be several hundred feet away from my house using Pandora and still on Wifi. When I turn the corner, 3G goes on and Pandora cuts out because it lost Wifi. Again, another very practical use of this technology.
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You're right but consider this scenario. You're at a coffee shop that offers wifi and you also have mobile network. You're streaming something to your phone which naturally prefers the wifi network. You get up and walk away and lose wifi. The TCP connection is lost, even though you have a perfectly good moble network also available. The TCP connection needs to be reestablished.
With multipath TCP in the same scenario your phone would have the option of setting up two TCP connections, one over each network. It would present a single socket to the streaming application (who is none the wiser). The multipath TCP socket sends packets over both networks (using whatever spread it feels appropriate). When you walk out of the coffee shop and lose the wifi the multipath TCP socket would stop using the dead network and only use the good network (mobile in this case). No loss in connection.