Improving Multipath TCP

Preamble The 20th century has seen the digital revolution, introducing the change from analog to digital technology. It is continuing right into the 21st century, interconnecting billions of digital devices over the Internet. Different types of devices and ways of communication have been designed. From smartphones to personal computers; from small servers connected to the Internet to huge content delivery networks serving millions of users simultaneously. The scale of the Internet and the mass of traffic it is transporting is continuously increasing [LIJM + 11]. In order to cope with this increasing amount of traffic, redundancy and load-balancing is the rule on the Internet. Indeed, there often exist many different paths between any two pair of hosts connected to the Internet. Internet Service Providers (ISPs) extensively use redundant paths to be resilient against link-failures. The load along these redundant paths is often balanced by using techniques like Equal Cost Multipath which distribute the traffic across multiple paths. Data centers have a similar incentive like ISPs to balance the load and be resilient against link failures. Finally, end-user devices also employ such kind of redundancy. Smart-phones are typically equipped with a WiFi and a 3G/4G interface. This allows to remain connected to the Internet, even if the next WiFi access point is far away. It becomes obvious that the Internet architecture offers a large number of paths between the end hosts. There remains however one problem. The protocols in use today are not able to efficiently use these paths. The most used protocol is the Transmission Control Protocol (TCP). It allows to send a byte stream in a reliable and in-order manner between two devices. It uses the IP addresses and port numbers to identify to which connection the payload belongs to. In order to steer a packet along a specific path, the IP address (or port numbers) must change. This would effectively break TCP's way of demultiplexing, making it unable to reconstruct the byte stream. There is a gap between the single-path transport protocols and the multi-path network. Multipath TCP, a recently proposed TCP extension, attempts to fill this gap. It extends TCP to allow transmitting a single byte stream across different paths. i ii Preamble This kind of multipath transmission has several benefits. First, it increases the resilience to failures. If a link disappears, Multipath TCP can simply continue the transmission on another one-without disrupting the byte stream. Second, …