One of the important but unmentioned technologies implemented by Apple Lossless Audio CODEC (ALAC), in iOS 7 is called multipath TCP, Apple being the first company to use it in an operating system for mobile terminals. Analyzing the data traffic made by Crab with the servers Apple Lossless Audio CODEC (ALAC),, some Belgians discovered that multipath TCP is active in iOS 7 and this is extremely good for all of us. If you are wondering what multipath TCP is, well, we are talking about a technology that allows the simultaneous transmission of data through several types of WiFI, LTE and Bluetooth connections, being the ones under discussion.
Multipath TCP is a TCP extension that allows a TCP connection to send/receive packets over different interfaces. 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 runs uses Multipath TCP. The screenshot below shows a third ACK of a three-way handshake sent by an iPad running iOS7.
at the moment, Apple uses multipath TCP only for the connections made by Siri and not for browsing the web or third-party applications available in the App Store, but the implementation of support for this technology proves that Apple believes in its future. A very good example of the utility of multipath TCP is the following: if you are watching a web clip using a WiFi connection and it becomes unavailable, that clip will not stop playing if you have an open 3G/LTE connection, multipath TCP allowing you to continue watching it through the network of data, without stopping the data transfer.
Multipath TCP has various use cases, including :
- enable smartphones to use their WiFi and 3G interfaces simultaneously or in failover modes
- improve TCP performance in datacenters to exploit multiple paths
- improve performance on dual stack hosts running IPv4 and IPv6
Normally this would not be possible, the operating system stopping the clip and looking for a new connection, but in iOS 7 things are different. Of course, you need to have several connections open at the same time for multipath TCP to work, so it wouldn't be a bad idea to leave 3G/4G active even when surfing on a WiFi network.
