updated 12:10 am EDT, Fri September 20, 2013
iPhone can transmit data over Wi-Fi, 3G/LTE, Bluetooth simultaneously
In addition to offering the first consumer smartphones with a 64-bit processor, Apple's iOS 7 update has apparently become the first major commercial software to be released with a working implementation of "multipath TCP" (MCTCP). The technology allows devices to stay connected to the Internet over both Wi-Fi and 3G or LTE simultaneously, allowing each to act as a fallback to the other in cases of weak signal. It can also maintain certain kinds of connections over Bluetooth or Ethernet as well, using all connections at once if needed.
The technique does not require any additional or advanced hardware, meaning all iPhones that can run iOS 7 can utilize the technology for more reliable connections. While the most common use would be to allow cellular data to seamlessly keep a faltering Wi-Fi connection alive without losing any data, it has other applications as well for areas like telephony and IP TV. Apple's implementation is evident in Siri, which under iOS 7 can continue communicating with Apple's servers to assist in voice recognition even when Wi-Fi service is intermittent.
First implemented on the Linux kernel, the technology is intended to create more robust connections that better utilize local networks, improve throughput and increase reliability by allowing networks to instantly work around any path failures. Under current TCP technology, if a connection falters (such as walking out of range of Wi-Fi), the session is ended and must be restarted (though Apple has long used a "handshake" technology to make 3G/LTE resumption of dropped sessions relatively painless).
MCTCP allows the simultaneous use of multiple IP addresses or interfaces, meaning that existing application "see" only a single TCP connection and thus do not require any modifications. A video of the technology (seen below) demonstrates an SSH session being connected simultaneously through Ethernet, Wi-Fi and 3G. The session continues uninterrupted as researchers turn off one, then another of the connections.