Adaptive Caching of Distributed Components

Die Zugriffslokalität referenzierter Daten ist eine wichtige Eigenschaft verteilter Anwendungen. Lokales Zwischenspeichern abgefragter entfernter Daten (Caching) wird vielfach bei der Entwicklung solcher Anwendungen eingesetzt, um diese Eigenschaft auszunutzen. Anschliessende Zugriffe auf diese Daten können so beschleunigt werden, indem sie aus dem lokalen Zwischenspeicher bedient werden. Gegenwärtige Middleware-Architekturen bieten dem Anwendungsprogrammierer jedoch kaum Unterstützung für diesen nicht-funktionalen Aspekt. Die vorliegende Arbeit versucht deshalb, Caching als separaten, konfigurierbaren Middleware-Dienst auszulagern. Durch die Einbindung in den Softwareentwicklungsprozess wird die frühzeitige Modellierung und spätere Wiederverwendung caching-spezifischer Metadaten gewährleistet. Zur Laufzeit kann sich das entwickelte System außerdem bezüglich der Cachebarkeit von Daten adaptiv an geändertes Nutzungsverhalten anpassen.Locality of reference is an important property of distributed applications. Caching is typically employed during the development of such applications to exploit this property by locally storing queried data: Subsequent accesses can be accelerated by serving their results immediately form the local store. Current middleware architectures however hardly support this non-functional aspect. The thesis at hand thus tries outsource caching as a separate, configurable middleware service. Integration into the software development lifecycle provides for early capturing, modeling, and later reuse of cachingrelated metadata. At runtime, the implemented system can adapt to caching access characteristics with respect to data cacheability properties, thus healing misconfigurations and optimizing itself to an appropriate configuration. Speculative prefetching of data probably queried in the immediate future complements the presented approach

Entrega de conteúdos multimédia em over-the-top: caso de estudo das gravações automáticas

Doutoramento em Engenharia EletrotécnicaOver-The-Top (OTT) multimedia delivery is a very appealing approach for providing ubiquitous, exible, and globally accessible services capable of low-cost and unrestrained device targeting. In spite of its appeal, the underlying delivery architecture must be carefully planned and optimized to maintain a high Qualityof- Experience (QoE) and rational resource usage, especially when migrating from services running on managed networks with established quality guarantees. To address the lack of holistic research works on OTT multimedia delivery systems, this Thesis focuses on an end-to-end optimization challenge, considering a migration use-case of a popular Catch-up TV service from managed IP Television (IPTV) networks to OTT. A global study is conducted on the importance of Catch-up TV and its impact in today's society, demonstrating the growing popularity of this time-shift service, its relevance in the multimedia landscape, and tness as an OTT migration use-case. Catch-up TV consumption logs are obtained from a Pay-TV operator's live production IPTV service containing over 1 million subscribers to characterize demand and extract insights from service utilization at a scale and scope not yet addressed in the literature. This characterization is used to build demand forecasting models relying on machine learning techniques to enable static and dynamic optimization of OTT multimedia delivery solutions, which are able to produce accurate bandwidth and storage requirements' forecasts, and may be used to achieve considerable power and cost savings whilst maintaining a high QoE. A novel caching algorithm, Most Popularly Used (MPU), is proposed, implemented, and shown to outperform established caching algorithms in both simulation and experimental scenarios. The need for accurate QoE measurements in OTT scenarios supporting HTTP Adaptive Streaming (HAS) motivates the creation of a new QoE model capable of taking into account the impact of key HAS aspects. By addressing the complete content delivery pipeline in the envisioned content-aware OTT Content Delivery Network (CDN), this Thesis demonstrates that signi cant improvements are possible in next-generation multimedia delivery solutions.A entrega de conteúdos multimédia em Over-The-Top (OTT) e uma proposta atractiva para fornecer um serviço flexível e globalmente acessível, capaz de alcançar qualquer dispositivo, com uma promessa de baixos custos. Apesar das suas vantagens, e necessario um planeamento arquitectural detalhado e optimizado para manter níveis elevados de Qualidade de Experiência (QoE), em particular aquando da migração dos serviços suportados em redes geridas com garantias de qualidade pré-estabelecidas. Para colmatar a falta de trabalhos de investigação na área de sistemas de entrega de conteúdos multimédia em OTT, esta Tese foca-se na optimização destas soluções como um todo, partindo do caso de uso de migração de um serviço popular de Gravações Automáticas suportado em redes de Televisão sobre IP (IPTV) geridas, para um cenário de entrega em OTT. Um estudo global para aferir a importância das Gravações Automáticas revela a sua relevância no panorama de serviços multimédia e a sua adequação enquanto caso de uso de migração para cenários OTT. São obtidos registos de consumos de um serviço de produção de Gravações Automáticas, representando mais de 1 milhão de assinantes, para caracterizar e extrair informação de consumos numa escala e âmbito não contemplados ate a data na literatura. Esta caracterização e utilizada para construir modelos de previsão de carga, tirando partido de sistemas de machine learning, que permitem optimizações estáticas e dinâmicas dos sistemas de entrega de conteúdos em OTT através de previsões das necessidades de largura de banda e armazenamento, potenciando ganhos significativos em consumo energético e custos. Um novo mecanismo de caching, Most Popularly Used (MPU), demonstra um desempenho superior as soluções de referencia, quer em cenários de simulação quer experimentais. A necessidade de medição exacta da QoE em streaming adaptativo HTTP motiva a criaçao de um modelo capaz de endereçar aspectos específicos destas tecnologias adaptativas. Ao endereçar a cadeia completa de entrega através de uma arquitectura consciente dos seus conteúdos, esta Tese demonstra que são possíveis melhorias de desempenho muito significativas nas redes de entregas de conteúdos em OTT de próxima geração

Understanding and Improving the Performance of Web Page Loads

The web is vital to our daily lives, yet web pages are often slow to load. The inefficiency and complexity of loading web pages can be attributed to the dependencies between resources within a web page, which also leads to underutilization of the CPU and network on client devices. My thesis research seeks solutions that enable better use of the client-side CPU and network during page loads. Such solutions can be categorized into three types of approaches: 1) leveraging a proxy to optimize web page loads, 2) modifying the end-to-end interaction between client browsers and web servers, and 3) rewriting web pages. Each approach offers various benefits and trade-offs. This dissertation explores three specific solutions. First, CASPR is a proxy-based solution that enables clients to offload JavaScript computations to proxies. CASPR loads web pages on behalf of clients and transforms every page into a version that is simpler for clients to process, leading to a 1.7s median improvement in web page rendering for popular CASPR web pages. Second, Vroom rethinks how page loads work; in order to minimize dependencies between resources, it enables web servers to provide resource hints to clients and ensures that resources are loaded with proper prioritization. As a result, Vroom halves the median load times for popular news and sports websites. Finally, I conducted a longitudinal study to understand how web pages have changed over time and how these changes have affected performance.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163157/1/vaspol_1.pd

Ubiquitous Computing

The aim of this book is to give a treatment of the actively developed domain of Ubiquitous computing. Originally proposed by Mark D. Weiser, the concept of Ubiquitous computing enables a real-time global sensing, context-aware informational retrieval, multi-modal interaction with the user and enhanced visualization capabilities. In effect, Ubiquitous computing environments give extremely new and futuristic abilities to look at and interact with our habitat at any time and from anywhere. In that domain, researchers are confronted with many foundational, technological and engineering issues which were not known before. Detailed cross-disciplinary coverage of these issues is really needed today for further progress and widening of application range. This book collects twelve original works of researchers from eleven countries, which are clustered into four sections: Foundations, Security and Privacy, Integration and Middleware, Practical Applications

Knowledge-based web services for context adaptation.

The need for higher value, reliable online services to promote new Internet-based business models is a requirement facing many technologists and business leaders. This need coupled with the trend towards greater mobility of networked devices and consumers creates significant challenges for current and future systems developers. The proliferation of mobile devices and the variability of their capabilities present an overwhelming number of options to systems designers and engineers who are tasked with the development of next generation context adaptive software services. Given the dynamic nature of this environment, implementing solutions for the current set of devices in the held makes an assumption that this deployment situation is somehow fixed this assumption does little to support the future and longer term needs within the marketplace. To add to the complexity, the timeframes necessary to develop robust and adaptive online software services can be long by comparison, so that the development projects and their resources are often behind on platform support before the first release is launched to the public. New approaches and methodologies for engineering dynamic and adaptive online services will be necessary and, as will be shown, are in fact mandated by the regulation imposed by service level guarantees. These new techniques and technology are commercially useless unless they can be used in engineering practice. New context adaptation processes and architectures must be capable of performing under strict service level agreements those that will undoubtedly govern future business relationships between online parties. This programme of engineering study and research investigates several key issues found in the emerging area of context adaptation services for online mobile networks. As a series of engineering investigations, the work described here involves a wider array of technical activity than found in traditional doctoral work and this is reflected throughout the dissertation. First, a clear definition of industrial motivation is stated to provide the engineering foundation. Next, the programme focuses on the nature of contextual adaptation through product development projects. The development process within these projects results in several issues with the commercial feasibility of the technology. From this point, the programme of study then progresses through the lifecycle of the engineering process, investigating at each stage the critical engineering challenges. Further analysis of the problems and possible solutions for deploying such adaptive solutions are reviewed and experiments are undertaken in the areas of systems component and performance analysis. System-wide architectural options are then evaluated with specific interest in using knowledge-base systems as one approach to solving some of the issues in context adaptation. The central hypothesis is that due to the dynamic nature of context parameters, the concept of a mobile device knowledge base as a necessary component of an architectural solution is presented and justified through prototyping efforts. The utility of web ontologies and other "soft computing" technologies on the nature of the solution are also examined through the review of relevant work and the engineering design of the demonstration system. These technology selections are supported directly by the industrial context and mission. In the final sections, the architecture is evaluated through the demonstration of promising techniques and methods in order to confirm understanding and to evaluate the use of knowledge-bases, AI and other technologies within the scope of the project. Through the implementation of a context adaptation architecture as a business process workflow, the impact of future trends of device reconfiguration are highlighted and discussed. To address the challenge of context adaptation in reconftgurable device architectures, an evolutionary computation approach is then presented as a means to provide an optimal baseline on which a service may execute. These last two techniques are discussed and new designs are proposed to specifically address the major issues uncovered in timely collection and evaluation of contextual parameters in a mobile service network. The programme summary and future work then brings together all the key results into a practitioner's reference guide for the creation of online context adaptive services with a greater degree of intelligence and maintainability while executing with the term of a service level agreement

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

Cooperative determination on cache replacement candidates for transcoding proxy caching

The original publication is available at www.springerlink.comTranscoding proxy caching is an important technology for improving the services over Internet, especially in the environment of mobile computing systems. In this paper, we address cooperative determination on cache replacement candidates for transcoding proxies. An original model which determines cache replacement candidates on all candidate nodes in a coordinated fashion with the objective of minimizing the total cost loss is proposed. We formulate this problem as an optimization problem and present a low-cost optimal solution for deciding cache replacement candidates.Keqiu Li, Hong Shen and Francis Y.L. Chi