A Multipath Transport Protocol for Future Internet

Our work aims to assess a multipath transport protocol named MPTCP (Multipath TCP), especially the various congestion control and coupling mechanisms considered for this protocol. Many authors propose to take advantage of the multiple paths that are often available for a data flow to improve its performance and its robustness to the varying transmission conditions. The different layers of the TCP/IP stack have been considered. At the application level, some authors suggest to handle many simultaneous TCP sockets and to shuffle the data upon them, like PSockets (Parallel Sockets). Other authors propose to open many end-to-end sub-connections in the transport layer transparently for the application, like cTCP (Concurrent TCP). At the network layer, some routing protocols may use multiple paths to route packets, like CMR (Concurrent Multipath Routing). And some algorithms have also been proposed at the Link layer, to split the data flow over several channels, like McMAC (Multiple channel MAC). Multiple paths between two end-points may have different characteristics (i.e. capacity, latency, etc.), or diverse and varying traffic conditions. In consequence, packets using different paths may arrive out of sequence to the receiver. In this case, according to the classical cumulative acknowledgement mechanism of TCP, the data receiver sends back duplicate acknowledgements. With the TCP mechanism Fast Retransmit the data source may then misinterpret these duplicate acknowledgements as an indication of packet loss due to a congestion in the network, and then wrongly reduce its throughput. An efficient multipath protocol has then to be able to deal with these diversity of characteristics to optimize the throughput and to react nonetheless properly to any change. Transport protocols can take advantage of feedback mechanisms, through the acknowledgements for example, to gather end-to-end up-to-date information about each path. This information can then be used to optimize dynamically the control of the traffic on the multiple available paths, for instance moving the traffic away from a congested path. An IETF working group, Multipath TCP (MPTCP), has started in 2009 to specify a multipath transport protocol. The aims are to improve the performance of a multi-path flow, i.e. to be at least as good as a single-path flow on the best route, without consuming on