Abstract—Vehicular Internet access via open WLAN access points (AP) has been demonstrated to be a feasible solution to provide opportunistic data service to moving vehicles. Using an in situ deployment, however, such a solution does not provide worstcase performance guarantees due to unpredictable intermittent connectivity. On the other hand, a solution that tries to cover every point in an entire road network with APs (a full coverage) is not very practical due to prohibitive deployment and operational costs. In this paper, we introduce a new notion of intermittent coverage for mobile users, called α-coverage, which provides worst-case guarantees on the interconnection gap while using significantly fewer APs than needed for full coverage. We propose efficient algorithms to verify whether a given deployment provides α-coverage and approximation algorithms for determining an economic deployment of APs that will provide α-coverage. Our algorithms can also be used to supplement open WLAN APs in a region with appropriate number of additional APs that will provide worst-case guarantees on interconnection gap. We compare α-coverage with opportunistic access of open WLAN APs (modeled as a random deployment) via simulations over real-world road networks and show that using the same number of APs as in case of random deployment, α-coverage limits the interconnection gap to a much smaller distance. I.

We investigate if WiFi access can be used to augment 3G capacity. To understand the feasibility of 3G augmentation, we conduct a detailed study of 3G and WiFi access from moving vehicles, in three different cities. We find that the average 3G and WiFi availability across the testbeds is 87 % and 11%, respectively. We also find that, unlike stationary environments, WiFi throughput is lower than 3G throughput in mobile environments, and WiFi loss rates are higher. We then design a system, called Wiffler, that uses two key ideas—leveraging delay tolerance and fast switching. For delay tolerant applications, Wiffler uses a simple model of the environment to predict WiFi connectivity, and delays applications to offload more data on WiFi. But Wiffler delays applications only if it results in 3G savings. For applications that are extremely sensitive to delay or loss (e.g., VoIP), Wiffler quickly switches to 3G if WiFi is unable to successfully transmit the packet within a small time window. We implement and deploy Wiffler in our vehicular testbed. Both our implementation and trace-driven experiments show that Wiffler significantly increases 3G savings. For example, for a realistic workload, Wiffler reduces 3G usage by 45 % for a delay tolerance of 60 seconds. 1.

While computers and Internet access have growing penetration amongst schools in the developing world, intermittent connectivity and limited bandwidth often prevent them from being fully utilized by students and teachers. In this paper, we make two contributions to help address this problem. First, we characterize six weeks of HTTP traffic from a primary school outside of Bangalore, India, illuminating opportunities and constraints for improving performance in such settings. Second, we deploy an aggressive caching and prefetching engine and show that it accelerates a user’s overall browsing experience (apart from video content) by 2.8x. Unlike proxy-based techniques, our system is bundled as an open-source Firefox plugin and runs directly on client machines. This allows easy installation and configuration by end users, which is especially important in developing regions where a lack of permissions or technical expertise often prevents modification of internal network settings.

We investigate if WiFi access can be used to augment 3G capacity in mobile environments. We first conduct a detailed study of 3G and WiFi access from moving vehicles, in three different cities. We find that the average 3G and WiFi availability across the cities is 87 % and 11%, respectively. WiFi throughput is lower than 3G throughput, and WiFi loss rates are higher. We then design a system, called Wiffler, to augments mobile 3G capacity. It uses two key ideas— leveraging delay tolerance and fast switching—to overcome the poor availability and performance of WiFi. For delay tolerant applications, Wiffler uses a simple model of the environment to predict WiFi connectivity. It uses these predictions to delays transfers to offload more data on WiFi, but only if delaying reduces 3G usage and the transfers can be completed within the application’s tolerance threshold. For applications that are extremely sensitive to delay or loss (e.g., VoIP), Wiffler quickly switches to 3G if WiFi is unable to successfully transmit the packet within a small time window. We implement and deploy Wiffler in our vehicular testbed. Our experiments show that Wiffler significantly reduces 3G usage. For a realistic workload, the reduction is 45 % for a delay tolerance of 60 seconds.

are going to become an indispensable part of the modern day automotive experience. For people on the move, vehicular networks can provide critical network connectivity and access to real-time information. Infostations play a vital role in these networks by acting as gateways to the Internet and by extending network connectivity. In this context, an important question is “What is the minimum number of infostations that need to be deployed in an area in order to support vehicular applications?” Optimizing infostation density is vital to understanding and reducing the cost of deployment and management. In this paper, we examine the required infostation density in a highway scenario using different data dissemination models. We start from a simple analysis that captures the required density under idealized assumptions. We then run detailed QualNet simulations on both controlled and realistic vehicular traces to observe the information density trends in practical environments, and consequently propose techniques to improve dissemination performance and reduce the required infostation density. I.

The majority of people in rural developing regions do not have access to the World Wide Web. Traditional network connectivity technologies have proven to be prohibitively expensive in these areas. The emergence of new long-range wireless technologies provide hope for connecting these rural regions to the Internet. However, the network connectivity provided by these new solutions are by nature intermittent due to high network usage rates, frequent power-cuts and the use of delay tolerant links. Typical applications, especially interactive applications like web search, do not tolerate intermittent connectivity. In this paper, we present the design and implementation of Rural-Cafe, a system intended to support efficient web search over intermittent networks. RuralCafe enables users to perform web search asynchronously and find what they are looking for in one round of intermittency as opposed to multiple rounds of search/downloads. RuralCafe does this by providing an expanded search query interface which allows a user to specify additional query terms to maximize the utility of the results returned by a search query. Given knowledge of the limited available network resources, RuralCafe performs optimizations to prefetch pages to best satisfy a search query based on a user’s search preferences. In addition, RuralCafe does not require modifications to the web browser, and can provide single round search results tailored to various types of networks and economic constraints. We have implemented and evaluated the effectiveness of Rural-Cafe using queries from logs made to a large search engine, queries made by users in an intermittent setting, and live queries from a small testbed deployment. We have also deployed a prototype of RuralCafe in Kerala, India.

I would like to start by expressing my deepest gratitude to my advisor, Lakshminarayanan Subramanian (or just “Lakshmi”). It was Lakshmi who set me on the path toward my eventual area of research. Lakshmi has always been generous with his time, and never short on ideas or enthusiasm. Without Lakshmi’s courage to pursue the research that inspires him, I would not have found my own passion: to build systems that benefit people- as many people as much as possible by inventing ways to bring technology to people living outside of the privileged regions of the world. Contributors to this dissertation- This thesis is based on research that I performed over the past five years with many colleagues contributing directly to the work in this dissertation. Many people helped me along the way whose help I could not have done without. The RuralCafe user study would not have been possible without the help of Saleema Amershi and Aditya Dhananjay (Chapter 6.6). Our low bandwidth transport modeling and analysis (Chapter 3.1) was an effort largely attributable to Janardhan Iyengar and long discussions with Bryan Ford. Russell Power implemented the feature reduction algorithm for CIPs (Chapter 7.2.2) in his “spare time”. Our ELF deployments (Chapters 2.2 and 5.3) were only possible with help from David Hutchful.

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