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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Computer Science

Year Degree Awarded

2017

Month Degree Awarded

February

First Advisor

Donald F. Towsley

Subject Categories

OS and Networks | Systems Architecture

Abstract

Multi-Path TCP (MPTCP) is a new transport protocol that enables mobile devices to simultaneously use several physical paths through multiple network interfaces. MPTCP is particularly useful for mobile devices, which usually have multiple wireless interfaces such as IEEE 802.11 (WiFi), cellular (3G/LTE), and Bluetooth. However, applying MPTCP to mobile devices introduces new concerns since they operate in harsh environments with resource constraints due to intermittent path availability and limited power supply. The goal of this thesis is to resolve these problems so as to be able to practically deploy MPTCP in mobile devices.

The first part of the thesis develops a cross-layer path management approach that exploits information from the physical and medium access control layers to deal with intermittent path availability in mobile environment while increasing path utilization of MPTCP over lossy links. Experimental results show that this approach efficiently utilizes intermittently available WiFi paths, with throughput improvements of up to 72%.

In addition to the need to manage intermittent path availability, MPTCP must deal with the increased energy consumption due to simultaneous operation of multiple network interfaces. Hence, it is important to understand the energy consumption behavior to deploy MPTCP in mobile devices. We develop an energy model for MPTCP power consumption derived from experimental measurements. Experimental results show that the model accurately estimates the MPTCP energy consumption.

Based on the MPTCP energy model, we further explore conditions under which MPTCP is more energy-efficient than either standard TCP or MPTCP. Informed by this finding, we design and implement an energy-aware MPTCP variant for mobile devices. Experimental results show that our approach reduces power consumption compared to standard MPTCP by up to 80% for small file downloads and up to 15% for large file downloads, while preserving the availability and robustness benefits of MPTCP.

Finally, we study the impact of path asymmetry on MPTCP performance. Since path asymmetries frequently appear in mobile networks, it is crucial to design a MPTCP path scheduler that properly distributes traffic across available paths, which has different network characteristics such as round-trip time and bandwidth. We propose and implement a new MPTCP path scheduler, ECF (Earliest Completion First), that utilizes all relevant information about a path. Experimental results show that in the presence of path asymmetries ECF consistently utilizes all available paths more efficiently while mitigating out-of-order delay compared to the default scheduler.

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