Smart devices equipped with multiple network interfaces are becoming commonplace. Nevertheless, even though multiple interfaces can be used to connect to the Internet, their capabilities have not been fully utilized yet because the default TCP/IP stack supports only a single interface for communication. This situation is now changing due to the emergence of multipath protocols on different network stack layers. For example, many IP level approaches have been proposed utilizing tunneling mechanisms for hiding multipath transmission from the transport protocols. Several working groups under IEEE and IETF are actively standardizing multipath transmission on the link layer and transport layer. Application level approaches enable multipath transmission capability by establishing multiple transport connections and distributing data over them. Given all these efforts, it is beneficial and timely to summarize the state-of-the-art, compare their pros and cons, and discuss about the future directions. To that end, we present a survey on multipath transmission and make several major contributions: (1) we present a complete taxonomy pertaining to multipath transmission, including link, network, transport, application and cross layers; (2) we survey the state-of-the-art for each layer, investigate the problems that each layer aims to address, and make comprehensive assessment of the solutions; (3) based on the comparison, we identify open issues and pinpoint future directions for multipath transmission research.

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The Multipath Transport Control Protocol (MPTCP) is undergoing a rapid deployment after a recent and quick standardization. MPTCP allows a network node to use multiple network interfaces and IP paths concurrently, which can lead to several advantages for the user in terms of performance and reliability. In this paper, we describe an MPTCP implementation in the Network Simulator 3 (ns3), comparing it with both the Linux implementation and previous ns3 implementations. We show that it is compatible with the Linux implementation and that it has a desirable similar behavior in traffic handling. Our goal is to allow researchers develop and evaluate new features of MPTCP using our simulator in a much faster way than they would with a kernel implementation, hence boosting MPTCP research.