Migrating Unfairness Among Subflows in MPTCP With Network Coding for Wired–Wireless Networks

Recently, two new technologies have been introduced into the transport layer. One is network coding, and the other is multipath transmission control protocol (MPTCP). Network coding is introduced into the transport layer to enhance the performance of transmission control protocol (TCP) in wireless networks. Benefiting from multi-interface devices, MPTCP is proposed to make full use of the network resource. Theoretically, combining these two technologies can utilize resources more adequately. However, network coding and multipath transportation cannot collaborate well with each other because network coding invalidates the load-balancing feature of MPTCP congestion control schemes. In this paper, we first discuss the unfair congestion control issue in MPTCP combined with network coding (MPTCP/NC). Then, a new end-to-end congestion control solution, named Couple+, is presented to deal with the unfairness among subflows. In Couple+, sender tries to slightly slow down sending rate if the reason of packet loss is not decided. After judging of packet loss reason based on the characteristics of packet loss events, the rate will be recovered soon if the loss is caused by wireless error (wireless noise or collision) or be further reduced if the loss is caused by congestion. By simulation, we compare the performances of Couple+ and the previous congestion control scheme of MPTCP. The performance analysis proves that unfairness among subflows indeed exists, and our scheme can balance congestion among coded and noncoded subflows and can stay friendly with TCP flow.