UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2010 - 20133

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    Observing and Improving the Reliability of Internet Last-mile Links
    (2013) Schulman, Aaron David; Spring, Neil; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    People rely on having persistent Internet connectivity from their homes and mobile devices. However, unlike links in the core of the Internet, the links that connect people's homes and mobile devices, known as "last-mile" links, are not redundant. As a result, the reliability of any given link is of paramount concern: when last-mile links fail, people can be completely disconnected from the Internet. In addition to lacking redundancy, Internet last-mile links are vulnerable to failure. Such links can fail because the cables and equipment that make up last-mile links are exposed to the elements; for example, weather can cause tree limbs to fall on overhead cables, and flooding can destroy underground equipment. They can also fail, eventually, because cellular last-mile links can drain a smartphone's battery if an application tries to communicate when signal strength is weak. In this dissertation, I defend the following thesis: By building on existing infrastructure, it is possible to (1) observe the reliability of Internet last-mile links across different weather conditions and link types; (2) improve the energy efficiency of cellular Internet last-mile links; and (3) provide an incrementally deployable, energy-efficient Internet last-mile downlink that is highly resilient to weather-related failures. I defend this thesis by designing, implementing, and evaluating systems.
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    Automating Performance Diagnosis in Networked Systems
    (2012) McCann, Justin N.; Hicks, Michael W; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Diagnosing performance degradation in distributed systems is a complex and difficult task. Software that performs well in one environment may be unusably slow in another, and determining the root cause is time-consuming and error-prone, even in environments in which all the data may be available. End users have an even more difficult time trying to diagnose system performance, since both software and network problems have the same symptom: a stalled application. The central thesis of this dissertation is that the source of performance stalls in a distributed system can be automatically detected and diagnosed with very limited information: the dependency graph of data flows through the system, and a few counters common to almost all data processing systems. This dissertation presents FlowDiagnoser, an automated approach for diagnosing performance stalls in networked systems. FlowDiagnoser requires as little as two bits of information per module to make a diagnosis: one to indicate whether the module is actively processing data, and one to indicate whether the module is waiting on its dependents. To support this thesis, FlowDiagnoser is implemented in two distinct environments: an individual host's networking stack, and a distributed streams processing system. In controlled experiments using real applications, FlowDiagnoser correctly diagnoses 99% of networking-related stalls due to application, connection-specific, or network-wide performance problems, with a false positive rate under 3%. The prototype system for diagnosing messaging stalls in a commercial streams processing system correctly finds 93% of message-processing stalls, with a false positive rate of 2%.
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    Properties of a DTN Packet Forwarding Scheme Inspired By Themodynamics
    (2010) Mathew, Bipin; La, Richard J.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis, we develop a discrete time model of a recently proposed algorithm, inspired by thermodynamics, for message routing in Disruption Tolerant Networks (DTNs). We model the evolution of the temperature at the nodes as a stochastic switched linear system and show that the temperatures converge in distribution to a unique stationary distribution that is independent of initial conditions. The proof of this result borrows tools from Iterated Random Maps (IRMs) and Queuing theory. Lastly, we simulate the proposed algorithm, using a variety of mobility models, in order to observe the performance of the algorithm under various conditions.