SEARCH, REPLICATION AND GROUPING FOR UNSTRUCTURED P2P NETWORKS

In my dissertation, I present a suite of protocols that assist in efficient content location and distribution in unstructured Peer-to-Peer overlays. The basis of these schemes is their ability to learn from past interactions, increasing their performance with time. Peer-to-Peer (P2P) networks are gaining increasing attention from both the scientific and the large Internet user community. Popular applications utilizing this new technology offer many attractive features to a growing number of users. P2P systems have two basic functions: Content search and dissemination. Search (or lookup) protocols define how participants locate remotely maintained resources. In data dissemination, users transmit or receive content from single or multiple sites in the network. P2P applications traditionally operate under purely decentralized and highly dynamic environments. Unstructured systems represent a particularly interesting class of P2P networks. Peers form an overlay in an ad-hoc manner, without any guarantees relative to lookup performance or content availability. Resources are locally maintained, while participants have limited knowledge, usually confined to their immediate neighborhood in the overlay. My work aims at providing effective and bandwidth-efficient searching and data sharing. A suite of algorithms which provide peers in unstructured P2P overlays with the state necessary in order to efficiently locate, disseminate and replicate objects is presented. The Adaptive Probabilistic Search (APS) scheme utilizes directed walkers to forward queries on a hop-by-hop basis. Peers store success probabilities for each of their neighbors in order to efficiently route towards object holders. AGNO performs implicit grouping of peers according to the demand incentive and utilizes state maintained by APS in order to route messages from content holders towards interested peers, without requiring any subscription process. Finally, the Adaptive Probabilistic REplication (APRE) scheme expands on the state that AGNO builds in order to replicate content inside query intensive areas according to demand

Rapid Prototyping of Topology Control Algorithms by Graph Transformation

Topology control algorithms are used to improve the energy efficiency (or other quality parameters) of wireless sensor networks. In this paper, we propose a model-driven rapid prototyping approach for the kTC topology control algorithm to enable the fast implementation and the evaluation of its different variants, and consequently, to accelerate the network quality experimentation cycle. In our approach, wireless sensor networks are described by graph-based models, and three variants of the kTC topology control algorithm are implemented by graph transformation, which are then executed on input network descriptions to derive modified topologies whose quality is then measured in several contexts to be able to assess the achieved network quality improvement

SoS: self-organizing substrates

Large-scale networked systems often, both by design or chance exhibit self-organizing properties. Understanding self-organization using tools from cybernetics, particularly modeling them as Markov processes is a first step towards a formal framework which can be used in (decentralized) systems research and design.Interesting aspects to look for include the time evolution of a system and to investigate if and when a system converges to some absorbing states or stabilizes into a dynamic (and stable) equilibrium and how it performs under such an equilibrium state. Such a formal framework brings in objectivity in systems research, helping discern facts from artefacts as well as providing tools for quantitative evaluation of such systems. This thesis introduces such formalism in analyzing and evaluating peer-to-peer (P2P) systems in order to better understand the dynamics of such systems which in turn helps in better designs. In particular this thesis develops and studies the fundamental building blocks for a P2P storage system. In the process the design and evaluation methodology we pursue illustrate the typical methodological approaches in studying and designing self-organizing systems, and how the analysis methodology influences the design of the algorithms themselves to meet system design goals (preferably with quantifiable guarantees). These goals include efficiency, availability and durability, load-balance, high fault-tolerance and self-maintenance even in adversarial conditions like arbitrarily skewed and dynamic load and high membership dynamics (churn), apart of-course the specific functionalities that the system is supposed to provide. The functionalities we study here are some of the fundamental building blocks for various P2P applications and systems including P2P storage systems, and hence we call them substrates or base infrastructure. These elemental functionalities include: (i) Reliable and efficient discovery of resources distributed over the network in a decentralized manner; (ii) Communication among participants in an address independent manner, i.e., even when peers change their physical addresses; (iii) Availability and persistence of stored objects in the network, irrespective of availability or departure of individual participants from the system at any time; and (iv) Freshness of the objects/resources' (up-to-date replicas). Internet-scale distributed index structures (often termed as structured overlays) are used for discovery and access of resources in a decentralized setting. We propose a rapid construction from scratch and maintenance of the P-Grid overlay network in a self-organized manner so as to provide efficient search of both individual keys as well as a whole range of keys, doing so providing good load-balancing characteristics for diverse kind of arbitrarily skewed loads - storage and replication, query forwarding and query answering loads. For fast overlay construction we employ recursive partitioning of the key-space so that the resulting partitions are balanced with respect to storage load and replication. The proper algorithmic parameters for such partitioning is derived from a transient analysis of the partitioning process which has Markov property. Preservation of ordering information in P-Grid such that queries other than exact queries, like range queries can be efficiently and rather trivially handled makes P-Grid suitable for data-oriented applications. Fast overlay construction is analogous to building an index on a new set of keys making P-Grid suitable as the underlying indexing mechanism for peer-to-peer information retrieval applications among other potential applications which may require frequent indexing of new attributes apart regular updates to an existing index. In order to deal with membership dynamics, in particular changing physical address of peers across sessions, the overlay itself is used as a (self-referential) directory service for maintaining the participating peers' physical addresses across sessions. Exploiting this self-referential directory, a family of overlay maintenance scheme has been designed with lower communication overhead than other overlay maintenance strategies. The notion of dynamic equilibrium study for overlays under continuous churn and repairs, modeled as a Markov process, was introduced in order to evaluate and compare the overlay maintenance schemes. While the self-referential directory was originally invented to realize overlay maintenance schemes with lower overheads than existing overlay maintenance schemes, the self-referential directory is generic in nature and can be used for various other purposes, e.g., as a decentralized public key infrastructure. Persistence of peer identity across sessions, in spite of changes in physical address, provides a logical independence of the overlay network from the underlying physical network. This has many other potential usages, for example, efficient maintenance mechanisms for P2P storage systems and P2P trust and reputation management. We specifically look into the dynamics of maintaining redundancy for storage systems and design a novel lazy maintenance strategy. This strategy is algorithmically a simple variant of existing maintenance strategies which adapts to the system dynamics. This randomized lazy maintenance strategy thus explores the cost-performance trade-offs of the storage maintenance operations in a self-organizing manner. We model the storage system (redundancy), under churn and maintenance, as a Markov process. We perform an equilibrium study to show that the system operates in a more stable dynamic equilibrium with our strategy than for the existing maintenance scheme for comparable overheads. Particularly, we show that our maintenance scheme provides substantial performance gains in terms of maintenance overhead and system's resilience in presence of churn and correlated failures. Finally, we propose a gossip mechanism which works with lower communication overhead than existing approaches for communication among a relatively large set of unreliable peers without assuming any specific structure for their mutual connectivity. We use such a communication primitive for propagating replica updates in P2P systems, facilitating management of mutable content in P2P systems. The peer population affected by a gossip can be modeled as a Markov process. Studying the transient spread of gossips help in choosing proper algorithm parameters to reduce communication overhead while guaranteeing coverage of online peers. Each of these substrates in themselves were developed to find practical solutions for real problems. Put together, these can be used in other applications, including a P2P storage system with support for efficient lookup and inserts, membership dynamics, content mutation and updates, persistence and availability. Many of the ideas have already been implemented in real systems and several others are in the way to be integrated into the implementations. There are two principal contributions of this dissertation. It provides design of the P2P systems which are useful for end-users as well as other application developers who can build upon these existing systems. Secondly, it adapts and introduces the methodology of analysis of a system's time-evolution (tools typically used in diverse domains including physics and cybernetics) to study the long run behavior of P2P systems, and uses this methodology to (re-)design appropriate algorithms and evaluate them. We observed that studying P2P systems from the perspective of complex systems reveals their inner dynamics and hence ways to exploit such dynamics for suitable or better algorithms. In other words, the analysis methodology in itself strongly influences and inspires the way we design such systems. We believe that such an approach of orchestrating self-organization in internet-scale systems, where the algorithms and the analysis methodology have strong mutual influence will significantly change the way future such systems are developed and evaluated. We envision that such an approach will particularly serve as an important tool for the nascent but fast moving P2P systems research and development community

Designs and Analyses in Structured Peer-To-Peer Systems

Peer-to-Peer (P2P) computing is a recent hot topic in the areas of networking and distributed systems. Work on P2P computing was triggered by a number of ad-hoc systems that made the concept popular. Later, academic research efforts started to investigate P2P computing issues based on scientific principles. Some of that research produced a number of structured P2P systems that were collectively referred to by the term "Distributed Hash Tables" (DHTs). However, the research occurred in a diversified way leading to the appearance of similar concepts yet lacking a common perspective and not heavily analyzed. In this thesis we present a number of papers representing our research results in the area of structured P2P systems grouped as two sets labeled respectively "Designs" and "Analyses". The contribution of the first set of papers is as follows. First, we present the princi- ple of distributed k-ary search and argue that it serves as a framework for most of the recent P2P systems known as DHTs. That is, given this framework, understanding existing DHT systems is done simply by seeing how they are instances of that frame- work. We argue that by perceiving systems as instances of that framework, one can optimize some of them. We illustrate that by applying the framework to the Chord system, one of the most established DHT systems. Second, we show how the frame- work helps in the design of P2P algorithms by two examples: (a) The DKS(n; k; f) system which is a system designed from the beginning on the principles of distributed k-ary search. (b) Two broadcast algorithms that take advantage of the distributed k-ary search tree. The contribution of the second set of papers is as follows. We account for two approaches that we used to evaluate the performance of a particular class of DHTs, namely the one adopting periodic stabilization for topology maintenance. The first approach was of an intrinsic empirical nature. In this approach, we tried to perceive a DHT as a physical system and account for its properties in a size-independent manner. The second approach was of a more analytical nature. In this approach, we applied the technique of Master Equations, which is a widely used technique in the analysis of natural systems. The application of the technique lead to a highly accurate description of the behavior of structured overlays. Additionally, the thesis contains a primer on structured P2P systems that tries to capture the main ideas prevailing in the field

Irlen Syndrome and the reading process

The purpose of the project was to determine if a school-wide intervention for students demonstrating symptons of Irlen Syndrome would result in improvements in reading skills and a reduction in physical symptoms that might impede visual processing necessary for successful reading

Human Connection as a Treatment for Addiction

Research supports that social connection is important in both humans and animals. In humans, having a cohesive support/social network system and healthy attachments in childhood predict low risk of later addiction (i.e. substance use disorder), as does perceived support from a religious or other cohesive community. Moreover, personal characteristics such as identifying as religious or spiritual can predict low risk for addiction, but little is known about the intersection of neuroscience and religion/spirituality in this regard. Conversely, adverse childhood experiences (ACEs) have repeatedly been shown to predict later addiction. However, the role of the body’s neuro-hormonal responses, such as the endogenous opioid and oxytocin systems in this process merits further exploration, such as how the production or deprivation of endogenous opioids impact later substance use patterns. Existing research also provides evidence that individuals decrease pursuit of interpersonal connections and social bonds when they use substances that activate opioid receptors. This has been found with both substances of abuse and medications used to treat addiction (e.g., methadone, buprenorphine, naltrexone). Research has also demonstrated that addiction often results in situations of social isolation. However, it remains to be elucidated whether the substances of abuse physiologically meet that need for connection. Importantly, research across numerous fields indicates that intentionally increasing interpersonal connection may be an effective treatment for addiction. However, less is known about how specific characteristics of communities impact the quantity, quality, or effectiveness of care and support for a person with addiction [...]https://dc.etsu.edu/etsu_books/1292/thumbnail.jp

Integrating Data Science and Earth Science

This open access book presents the results of three years collaboration between earth scientists and data scientists, in developing and applying data science methods for scientific discovery. The book will be highly beneficial for other researchers at senior and graduate level, interested in applying visual data exploration, computational approaches and scientifc workflows

Integrating Data Science and Earth Science

This open access book presents the results of three years collaboration between earth scientists and data scientist, in developing and applying data science methods for scientific discovery. The book will be highly beneficial for other researchers at senior and graduate level, interested in applying visual data exploration, computational approaches and scientifc workflows

A network QoS management architecture for virtualization environments

Network quality of service (QoS) and its management are concerned with providing, guaranteeing and reporting properties of data flows within computer networks. For the past two decades, virtualization has been becoming a very popular tool in data centres, yet, without network QoS management capabilities. With virtualization, the management focus shifts from physical components and topologies, towards virtual infrastructures (VI) and their purposes. VIs are designed and managed as independent isolated entities. Without network QoS management capabilities, VIs cannot offer the same services and service levels as physical infrastructures can, leaving VIs at a disadvantage with respect to applicability and efficiency. This thesis closes this gap and develops a management architecture, enabling network QoS management in virtulization environments. First, requirements are dervied, based on real world scenarios, yielding a validation reference for the proposed architecture. After that, a life cycle for VIs and a taxonomy for network links and virtual components are introduced, to arrange the network QoS management task with the general management of virtualization environments and enabling the creation of technology specific adaptors for integrating the technologies and sub-services used in virtualization environments. The core aspect, shaping the proposed management architecture, is a management loop and its corresponding strategy for identifying and ordering sub-tasks. Finally, a prototypical implementation showcases that the presented management approach is suited for network QoS management and enforcement in virtualization environments. The architecture fulfils its purpose, fulfilling all identified requirements. Ultimately, network QoS management is one amongst many aspects to management in virtualization environments and the herin presented architecture shows interfaces to other management areas, where integration is left as future work.Verwaltungsaufgaben für Netzdienstgüte umfassen das Bereitstellen, Sichern und Berichten von Flusseigenschaften in Rechnernetzen. Während der letzen zwei Jahrzehnte entwickelte sich Virtualisierung zu einer Schlüsseltechnologie für Rechenzentren, bisher ohne Möglichkeiten zum Verwalten der Netzdienstgüte. Der Einsatz von Virtualisierung verschiebt den Fokus beim Betrieb von Rechenzentren weg von physischen Komponenten und Netzen, hin zu virtuellen Infrastrukturen (VI) und ihren Einsatzzwecken. VIs werden als unabhängige, voneinander isolierte Einheiten entwickelt und verwaltet. Ohne Netzdienstgüte, sind VIs nicht so vielseitig und effizient einsetzbar wie physische Aufbauten. Diese Arbeit schließt diese Lücke mit der Entwicklung einer Managementarchitektur zur Verwaltung der Netzdienstgüte in Virtualisierungsumgebungen. Zunächst werden Anforderungen aus realen Szenarios abgeleitet, mit denen Architekturen bewertet werden können. Zur Abgrenzung der speziellen Aufgabe Netzdienstgüteverwaltung innerhalb des allgemeinen Managementproblems, wird anschließend ein Lebenszyklusmodell für VIs vorgestellt. Die Entwicklung einer Taxonomie für Kopplungen und Komponenten ermöglicht technologiespezifische Adaptoren zur Integration von in Virtualisierungsumgebungen eingesetzten Technologien. Kerngedanke hinter der entwickelten Architektur ist eine Rückkopplungsschleife und ihre einhergehende Methode zur Strukturierung und Anordnung von Teilproblemen. Abschließend zeigt eine prototypische Implementierung, dass dieser Ansatz für Verwaltung und Durchsetzung von Netzdienstgüte in Virtualisierungsumgebungen geeignet ist. Die Architektur kann ihren Zweck sowie die gestellten Anforderungen erfüllen. Schlussendlich ist Netzdienstgüte ein Bereich von vielen beim Betrieb von Virtualisierungsumgebungen. Die Architektur zeigt Schnittstellen zu anderen Bereichen auf, deren Integration zukünftigen Arbeiten überlassen bleibt

Informing an integrated and sustainable urbanism through rapid, defragmented analysis and design

Urban design has splintered into increasingly narrow specialist disciplines since the mid Twentieth Century. Traffic engineers, statutory planners, civil engineers, landscape architects and architects each make specific but isolated contributions to urban design frameworks. Each consultant documents their position predominantly through text and two dimensional representations, occasionally with specious perspective images produced by a hand rendering specialist. This fragmented and sequential design approach inadequately addresses contemporary urban agendas, practice constraints or the potential of digital design techniques, particularly in light of increasing fears of an imminent environmental crisis and peak oil, and concerns for health, amenity and accommodating an increasingly urbanised population. The aim of my thesis is to identify and address disparities between contemporary urban design practice and society's prevailing urban agendas for integrated and sustainable cities. The hypothesis tested by my thesis is that the gulf between prevailing urban agendas of society and urban design can be reduced by developing a 'defragmented' design approach that uses rapid, parametric, four-dimensional, digital analysis and design techniques, which build upon software commonly available within the industry. This hypothesis has been tested in four ways: firstly through the analysis of urban agendas, design techniques and urban design paradigms, in both historic and contemporary contexts; secondly by identifying currently available technologies with the potential for adaptation and customisation; thirdly by development of new digital techniques; and finally by testing this defragmented approach on both simplified models and various case studies within an urban design practice as part of the embedded research program. Techniques I have developed and tested as part of the approach fit into four categories: firstly pedestrian connectivity - walkability and accessibility; secondly daylight amenity assessment; thirdly visual impact analysis assessing urban form visualisation, generation and composition; and finally feasibility modelling, including linked data yield analysis. I have evaluated the success of the approach in these studies with regard to practice constraints (time and budget) and contemporary society's pr evailing urban agendas. My rapid, defragmented design approach has resulted in new techniques shown to be used quickly and concurrently 'in-house' contributing to the urban design process, whilst meeting fee budgets and project deadlines. I have demonstrated that issues that are currently difficult to solve using the constraints of conventional planning techniques can be addressed more effectively than they are currently, whilst avoiding the considerable expense of specialised hardware/software or the appointment of additional consultants. My thesis concludes that the rapid, defragmented approach can demonstrably yield more synergistic urban design responses. The inherently flexible approach can be tailored for a myriad of different urban design scenarios, as well as potentially other disciplines. The defragmented approach can expand the realm of urban designers and increase their contribution in the generation and advocacy of sustainable planning policy and reduce the disparities between contemporary urban design practice and society's need for integrated and sustainable cities