R-MPTCP: a rank-based data scheduler for wireless networks

The Multi-Path Transmission Control Protocol (MPTCP) leverages multiple network interfaces available in multi-homing devices to optimize performance and aggregate bandwidth over the Internet. However, MPTCP is not completely immune to the inherent challenges of multipathing, as packet losses and path heterogeneity in terms of available bandwidth, Packet Loss Rate (PLR), and delay cause severe reordering issues. The continual receipt of Out-oF-Order (OFO) packets eventually leads to excessive Receiver Buffer Blocking (RBB), needless congestion window (cwnd) adaptations, and unnecessary retransmissions. These actions deteriorate application-level throughput performance, which in turn affects the user’s Quality of Experience (QoE) and Quality of Service (QoS). Therefore, the MPTCP scheduler requires an appropriate cwnd adaptation policy that wisely deals with packet losses and path heterogeneity. Such a policy could help MPTCP attain maximum path utilization, eventually leading to enhanced throughput performance. This paper presents a path Rank-based MPTCP scheduler (R-MPTCP) that adjusts cwnd growth based on path rank. The rank is dynamically determined by considering each path’s successful transmission rate. A fast retransmission policy is additionally presented, which selects the highest-ranked path to retransmit lost or timed-out packets, helping to recover from packet loss and timeouts more effectively. The simulation results show that R-MPTCP performs better than existing variants regarding throughput and file transfer time under various PLRs, bandwidth, and latency.