Jim Martin

Delay-based congestion avoidance for TCP

The set of TCP congestion control algorithms associated with TCP/Reno (e.g., slow-start and congestion avoidance) have been crucial to ensuring the stability of the Internet. Algorithms such as TCP/NewReno (which has been deployed) and TCP/Vegas (which has not been deployed) represent incrementally deployable enhancements to TCP as they have been shown to improve a TCP connections throughput without degrading performance to competing flows. Our research focuses on delay-based congestion avoidance algorithms (DCA), like TCP/Vegas, which attempt to utilize the congestion information contained in packet round-trip time (RTT) samples. Through measurement and simulation, we show evidence suggesting that a single deployment of DCA (i.e., a TCP connection enhanced with a DCA algorithm) is not a viable enhancement to TCP over high-speed paths. We define several performance metrics that quantify the level of correlation between packet loss and RTT. Based on our measurement analysis we find that although there is useful congestion information contained within RTT samples, the level of correlation between an increase in RTT and packet loss is not strong enough to allow a TCP/Sender to reliably improve throughput. While DCA is able to reduce the packet loss rate experienced by a connection, in its attempts to avoid packet loss, the algorithm will react unnecessarily to RTT variation that is not associated with packet loss. The result is degraded throughput as compared to a similar flow that does not support DCA.

The efficacy of live virtual machine migrations over the internet

This paper describes a technique to enable live migration of virtual machines over the Internet. The method assumes the network supports Mobile IPv6 and that participating host devices support Xen 3.1. Unlike live migration schemes proposed by other researchers, virtual networks are not required. We describe our work in progress on developing a system that utilizes Mobile IPv6 to enable constant network connectivity through the migration. We identify the sources of delay associated with the live migration and conclude that as long as migrations occur relatively infrequently, live migration over the Internet is practical.

The incremental deployability of RTT-based congestion avoidance for high speed TCP Internet connections

Our research focuses on end-to-end congestion avoidance algorithms that use round trip time (RTT) fluctuations as an indicator of the level of network congestion. The algorithms are referred to as delay-based congestion avoidance or DCA. Due to the economics associated with deploying change within an existing network, we are interested in an incrementally deployable enhancement to the TCP/Reno protocol. For instance, TCP/Vegas, a DCA algorithm, has been proposed as an incremental enhancement. Requiring relatively minor modifications to a TCP sender, TCP/Vegas has been shown to increase end-to-end TCP throughput primarily by avoiding packet loss. We study DCA in todays best effort Internet where IP switches are subject to thousands of TCP flows resulting in congestion with time scales that span orders of magnitude. Our results suggest that RTT-based congestion avoidance may not be reliably incrementally deployed in this environment. Through extensive measurement and simulation, we find that when TCP/DCA (i.e., a TCP/Reno sender that is extended with DCA) is deployed over a high speed Internet path, the flow generally experiences degraded throughput compared to an unmodified TCP/Reno flow. We show (1) that the congestion information contained in RTT samples is not sufficient to predict packet loss reliably and (2) that the congestion avoidance in response to delay increase has minimal impact on the congestion level over the path when the total DCA traffic at the bottleneck consumes less than 10% of the bottleneck bandwidth.

Balancing Spectral Efficiency, Energy Consumption, and Fairness in Future Heterogeneous Wireless Systems with Reconfigurable Devices

In this paper, we present an approach to managing resources in a large-scale heterogeneous wireless network that supports reconfigurable devices. The system under study embodies internetworking concepts requiring independent wireless networks to cooperate in order to provide a unified network to users. We propose a multi-attribute scheduling algorithm implemented by a central Global Resource Controller (GRC) that manages the resources of several different autonomous wireless systems. The attributes considered by the multi-attribute optimization function consist of system spectral efficiency, battery lifetime of each user (or overall energy consumption), and instantaneous and long-term fairness for each user in the system. To compute the relative importance of each attribute, we use the Analytical Hierarchy Process (AHP) that takes interview responses from wireless network providers as input and generates weight assignments for each attribute in our optimization problem. Through Matlab/CPLEX based simulations, we show an increase in a multi-attribute system utility measure of up to 57% for our algorithm compared to other widely studied resource allocation algorithms including Max-Sum Rate, Proportional Fair, Max-Min Fair and Min Power.

Smart Grid communication using next generation heterogeneous wireless networks

In this paper, we present a Smart Grid Home Area Network communication infrastructure solution that is based on future next generation heterogeneous wireless systems. The heterogeneous wireless system is composed of several Radio Access Technologies (RATs) available at consumer premises. The smart devices that use Smart Grid applications are assumed to have reconfigurable radios. A centralized Global Resource Controller (GRC) instructs the smart devices to use a particular RAT at any given time. The device-to-RAT association is made by the GRC using a two-step scheduling algorithm that accounts for the requirements of both best-effort and real-time Smart Grid traffic. To make the solution scalable, the approach utilizes Dynamic Spectrum Access methods to obtain additional open spectrum. We show up to 80% increase in real-time traffic support and 726% increase in best-effort traffic support in our proposed heterogeneous wireless system that uses reconfigurable radios, compared to the homogeneous wireless networks used today by smart devices with static radios.

Performance Characteristics of an Operational WiMAX Network

The term WiMAX is used to refer to a collection of standards, products, and service offerings derived from the IEEE 802.16 family of standards for wireless networks. These standards define physical and MAC layer elements that ensure interoperability of compatible equipment. However, the standards leave both the details of the packet scheduling algorithms and the values of performance related configuration parameters to the discretion of the equipment vendor or network operator. These algorithms and parameters ultimately determine fundamental performance characteristics such as round-trip latency and sustainable throughput on the network. In this paper, we examine performance characteristics of an operational WiMAX testbed upon which we were able to conduct controlled experiments in the absence of competing traffic. We characterize latency, throughput, protocol overhead, and the impact of WiMAX on TCP dynamics. We show that scheduling policies and parameter values impact actual performance in ways that are not possible to characterize in generic studies of WiMAX.

A Fast Cloud-Based Network Selection Scheme Using Coalition Formation Games in Vehicular Networks

Leveraging multiple wireless technologies and radio access networks (RANs), vehicles on the move have the potential to get robust connectivity and continuous service. To support the demands of as many vehicles as possible, an efficient and fast network selection scheme is critically important to achieve high performance and efficiency. So far, prior works have primarily focused on design of optimization algorithms and utility functions for either user or network performance. Most such studies do not address the complexities involved in the acquisition of needed information and the execution of algorithms, making them unsuitable for practical implementations in vehicles. This paper proposes a fast cloud-based network selection scheme for vehicular networks. By leveraging a compute clouds abundant computing and data storage resources, vehicles can leverage wider scope network information for decision-making. Vehicles select best access networks through a coalition formation game approach. A one-iteration fast convergence algorithm is proposed to achieve the final state of coalition structure in the game. Through extensive simulation, the proposed network selection scheme was shown to balance system throughput and fairness with a built-in utility division rule of the framework. The algorithm efficiency showed eightfold enhancement over a conventional coalition formation algorithm. Such features validate the potential of implementation in practice.

An OpenFlow Testbed for the Evaluation of Vertical Handover Decision Algorithms in Heterogeneous Wireless Networks

This paper details a framework that leverages Software Defined Networking (SDN) features to provide a testbed for evaluating handovers for IPv4 heterogeneous wireless networks. The framework is intended to be an extension to the Global Environment for Network Innovations (GENI) testbed, but the essence of the framework can be applied on any OpenFlow (OF) enabled network. Our goal is to enable researchers to evaluate vertical handover decision algorithms using GENI resources, open source software, and low cost commodity hardware. The framework eliminates the triangle routing problem experienced by other previous IPv4-compatible IP mobility solutions. This paper provides an overview of the testbed framework, implementation details for our installation using GENI WiMAX resources, and a discussion of future work.

An Efficient Wireless Power Transfer System to Balance the State of Charge of Electric Vehicles

As an alternate form in the road transportation system, electric vehicle (EV) can help reduce the fossil-fuel consumption. However, the usage of EVs is constrained by the limited capacity of battery. Wireless Power Transfer (WPT) can increase the driving range of EVs by charging EVs in motion when they drive through a wireless charging lane embedded in a road. The amount of power that can be supplied by a charging lane at a time is limited. A problem here is when a large number of EVs pass a charging lane, how to efficiently distribute the power among different penetrations levels of EVs? However, there has been no previous research devoted to tackling this challenge. To handle this challenge, we propose a system to balance the State of Charge (called BSoC) among the EVs. It consists of three components: i) fog-based power distribution architecture, ii) power scheduling model, and iii) efficient vehicle-to-fog communication protocol. The fog computing center collects information from EVs and schedules the power distribution. We use fog closer to vehicles rather than cloud in order to reduce the communication latency. The power scheduling model schedules the power allocated to each EV. In order to avoid network congestion between EVs and the fog, we let vehicles choose their own communication channel to communicate with local controllers. Finally, we evaluate our system using extensive simulation studies in Network Simulator-3, MatLab, and Simulation for Urban MObility tools, and the experimental results confirm the efficiency of our system.

WiMAX performance at 4.9 GHz

Worldwide Interoperability for Microwave Access (referred to as WiMAX) is a MAC and physical layer wireless communications technology for outdoor broadband wireless coverage. In collaboration with the Clemson University Police Department, we have deployed an 802.16d WiMAX network that operates at 4.9 GHz at Clemson University. In this paper, we present the results from a performance analysis we have conducted of the WiMAX network. To the best of our knowledge the work reported in this paper is the first academic study of an operational 4.9 GHz WiMAX in which controlled experiments could be conducted. While neither the 4.9 GHz spectrum nor the current WiMAX profiles settings might be optimal for space or lunar communications, a study of WiMAX at any frequency is of value to both the aerospace industry and the research community. The WiMAX standard leaves key areas of the protocol, including packet scheduling, frame packing, and modulation/coding adaptation, unspecified. In order to accurately model and analyze WiMAX, realistic assumptions must be used. Because WiMAX systems have not been widely studied, there is a disconnect between theoretical WiMAX systems and real-world deployed systems. This motivates the research presented in this paper. Using knowledge of the equipments implementation choices, we derive theoretical application throughput for both TCP and UDP protocols and correlate expected results with empirical results. We also summarize results from a coverage analysis of the system. The combined results lead to an important point: although equipment implementation choices contribute to the achieved performance of WiMAX, the physics surrounding 4.9 GHz RF propagation will likely have the most significant impact on system performance.12