MCTCP: A Multipath Transport Shim Layer

Multipath transport protocols enable the concurrent use of different paths and resource pooling of their capacity. Ongoing research and standardization activities extend the Transmission Control Protocol (TCP) towards a Multipath TCP solution. The objective is to aggregate multiple subflows between two endpoints into a single session that can be accessed by an application like a single TCP connection. This paper presents and evaluates Multi-Connection TCP (MCTCP) as a new multipath transport solution. MCTCP consists of a shim layer on top of several TCP connections and encodes control information, as far as possible, in their payload. In this paper, we first motivate MCTCP's design and compare it to a multipath transport protocol that uses TCP option encoding only. Second, we show that MCTCP can be implemented in the Linux stack with very few kernel modifications. We also demonstrate that MCTCP can be combined with a coupled multipath congestion control mechanism. Measurement results prove that MCTCP is an efficient and robust protocol that can dynamicall.y pool the bandwidth of several paths.