Goodput improvement for multipath TCP by congestion window adaptation in multi-radio devices

Multipath Transport Control Protocol (MPTCP) has been standardized by Internet Engineering Task Force (IETF) to support simultaneous delivery of transport control protocol (TCP) packets over multiple interfaces of multi-radio mobile devices. Although MPTCP provides an efficient solution to aggregate the available bandwidth of multiple paths, the goodput of MPTCP is usually far lower than the aggregate throughput due to out-of-order received packets. One key reason for the out-of-order issue is the large variation of end-to-end delay for multiple paths over wireless channels. In this paper, we propose a congestion window adaption algorithm for the MPTCP source (referred to as CWA-MPTCP), which dynamically adjusts the congestion window for each TCP subflow so as to mitigate the variation of end-to-end path delay. We consider typical multipath transmission scenarios over wireless links, as well as a cooperative multi-hop wireless network with multiple relays. For wired paths with stable end-to-end delay, we further develop a proactive scheduling algorithm to determine the packet sending sequence to each path. This algorithm effectively reduces the out-of-order packets by predicting the receiving sequence. Experiments are conducted to evaluate the goodput performance of the two enhancements to MPTCP. Significant performance gain is achieved in terms of goodput, while the receive buffer requirement is minimized.