Multi-path TCP extension for multimedia QoS in wireless networks

Abstract

Multi-Path TCP (MPTCP) has attracted much attention as a promising technology to improve throughput performance of wireless devices that support multi-homed heterogeneous networks. Although MPTCP provides significant increase in network capacity, it may suffer from poor delay performance since the delay tends to be aligned with the worst-performing path: packets delivered through a short-delay subflow have to wait in the reordering buffer for packets being transmitted over a long-delay subflow. In this dissertation, we address the application-level delay problem of MPTCP and propose three different solutions that aim to improve delay performance of MPTCP and link utilization of bottleneck links. First, we provide the analytical framework of the application-level delay of MPTCP in wireless networks based on queueing theory. Based on the framework, we formulate the network utility minimization problem considering delay and throughput performance. Our proposed traffic splitting scheme (TSC) minimizes the network cost, as well as control application traffic. We use ns-3 simulation to verify delay distribution of delivered traffic and evaluate the proposed rate control scheme. Second, we extend the traffic splitting scheme to design a receiver-side window control scheme. For window control, we develop an analytical framework of application-level delay to take into account non-negligible network queuing delay and the interplay of congestion control between multiple subflows. We design a simple threshold-based subflow traffic allocation scheme that aims to minimize user-level delay and develop a receiver centric traffic splitting control (R-TSC) that can be tuned to user preferences. The receiver-side R-TSC solution facilitates incremental deployment of low-delay streaming services over MPTCP. Lastly, we reveal that Droptail queue with various buffer space and CoDeL shows low link utilization under varying wireless capacity, and propose a scheme that aims to exploit multiple subflows on single path using MPTCP. Adaptation of subflows in number along with receiver-centric CoDeL achieves high link utilization and small delay simultaneously. Potentially, it can be extended to a scenario of using multiple networks. Through simulation and testbed experiments using commercial LTE and WiFi networks, we demonstrate significant performance gains of the proposed scheme over the standard MPTCP protocol.