News for multipath TCP

http://arstechnica.com/apple/2013/09/multipath-tcp-lets-siri-seamlessly-switch-between-wi-fi-and-3glte/

In theory, a router could just load balance packets over two or more paths by sending packet 1 over path A, packet 2 over path B, 3 over A, 4 over B, and so on. It turns out that this doesn't work so well, because one path is always a bit faster than the other path, meaning packets will arrive out of order. For instance, if path A is a bit shorter or path B has a bit more traffic, packet 3 may arrive at the receiver before packet 2. If this happens too often, TCP thinks packets were lost because it was transmitting too fast. So it slows down, which is not what we want.

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MPTCP avoids these issues by having the sending system determine which packets go down which path. It can then measure the properties of each path independently and send more packets over the faster path. This is a key part of MPTCP, because without it, the system would simply send half of its traffic over a 10Mbps path and the other half over a 100Mbps path (the system would impose the limit of the first on the second, splitting the delivery equally for a total of 20Mbps). By dynamically balancing traffic, MPTCP can use the full 110Mbps in this scenario. And if one path stops working, it is smart enough to retransmit any lost packets over another, working path. This part seems to be the thing that Apple is after by having Siri use MPTCP.

http://www.technologyreview.com/news/519646/how-apple-could-boost-speeds-20-times-on-the-next-iphone/

http://www.idownloadblog.com/2013/09/24/apple-using-multi-path-tcp/