Olivier Bonaventure

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Apple seems to also believe in Multipath TCP

Multipath TCP is a TCP extension that allows a TCP connection to send/receive packets over different interfaces. Multipath TCP has various use cases, including :

Designing such a major TCP extension has been a difficult problem and took a lot of effort within several research projects. The work started within the FP7 Trilogy project funded by the European Commission. It continues within the CHANGE and Trilogy 2 projects.

After five years of effort, we are getting close to a wide adoption of Multipath TCP.

  • In January 2013, the IETF published the Multipath specification as an Experimental standard in RFC 6824
  • In July 2013, the MPTCP working group reported three independent implementations of Multipath TCP, including our implementation in the Linux kernel. To my knowledge, this is the first time that a large TCP extension is implemented so quickly.
  • On September 18th, 2013, Apple releases iOS7 which includes the first large scale commercial deployment of Multipath TCP. Given the marketing buzz around new iOS7 releases, when can expect tens of millions of users who will use a Multipath TCP enabled device.

Packet traces collected on an iPad running iOS7 reveal that it uses Multipath TCP to reach some destinations that seem to be directly controlled by Apple. You won’t see Multipath TCP for regular TCP connections from applications like Safari, but if you use SIRI, you might see that the connection with one of the apple servers uses Multipath TCP. The screenshot below shows the third ACK of a three-way handshake sent by an ipad running iOS7.

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At this stage, the actual usage of Multipath TCP by iOS7 is unclear to me. If you have any hint on the type of information exchanged over this SSL connection, let me know.

The next step will, of course, be the utilisation of Multipath TCP by default for all applications running over iOS7.