Packet Scheduling in Multipath TCP: Fundamentals, Lessons, and Opportunities

Multipath transmission control protocol (MPTCP) is a transport protocol that allows the simultaneous use of multiple transmission control protocol subflows across the existing IP addresses between peers. Since each subflow undergoes the bottleneck link condition of its path, selecting the best subflow to schedule an outgoing packet plays a key role in the multipath performance. While good scheduling decisions can significantly improve throughput, wrong decisions prevent users from benefiting the aggregating capacities of available subflows. To deal with this concern, in the last years, several scheduling solutions were proposed to achieve different goals and applications. Different from other surveys and tutorials, in this article, we provide a tutorial of packet scheduling in the MPTCP that brings not only its fundamentals but also a detailed analysis of multipath performance from a consistent experimental methodology. In a multipath network setup, we compare single-criterion and multicriteria schedulers under different bottleneck conditions and multipath congestion controls. From a comprehensive experimental analysis that unveils several performance issues, we discuss the lessons learned and research opportunities regarding the multipath throughput improvement as the central motivation. In this way, this article provides a comprehensive analysis of packet scheduling in the MPTCP, not only in theory but in practice as well.