Over the last decade, live video streaming applications have gained great popularity among users but put great pressure on video servers and the Internet. In order to satisfy the growing demands for live video streaming, Peer-to-Peer(P2P) has been developed to relieve the video servers of bandwidth bottlenecks and computational load. Furthermore, Network Coding (NC) has been proposed and proved as a significant breakthrough in information theory and coding theory. According to previous research, NC not only brings substantial improvements regarding throughput and delay in data transmission, but also provides innovative solutions for multiple issues related to resource allocation, such as the coupon-collection problem, allocation and scheduling procedure. However, the complex NC-driven P2P streaming network poses substantial challenges to the packet scheduling algorithm. This thesis focuses on the packet scheduling algorithm for video multicast in NC-driven P2P streaming network. It determines how upload bandwidth resources of peer nodes are allocated in different transmission scenarios to achieve a better Quality of Service(QoS). First, an optimized rate allocation algorithm is proposed for scalable video transmission (SVT) in the NC-based lossy streaming network. This algorithm is developed to achieve the tradeoffs between average video distortion and average bandwidth redundancy in each generation. It determines how senders allocate their upload bandwidth to different classes in scalable data so that the sum of the distortion and the weighted redundancy ratio can be minimized. Second, in the NC-based non-scalable video transmission system, the bandwidth ineffi- ciency which is caused by the asynchronization communication among peers is reduced. First, a scalable compensation model and an adaptive push algorithm are proposed to reduce the unrecoverable transmission caused by network loss and insufficient bandwidth resources. Then a centralized packet scheduling algorithm is proposed to reduce the unin- formative transmission caused by the asynchronized communication among sender nodes. Subsequently, we further propose a distributed packet scheduling algorithm, which adds a critical scalability property to the packet scheduling model. Third, the bandwidth resource scheduling for SVT is further studied. A novel multiple- generation scheduling algorithm is proposed to determine the quality classes that the receiver node can subscribe to so that the overall perceived video quality can be maxi- mized. A single generation scheduling algorithm for SVT is also proposed to provide a faster and easier solution to the video quality maximization function. Thorough theoretical analysis is conducted in the development of all proposed algorithms, and their performance is evaluated via comprehensive simulations. We have demon- strated, by adjusting the conventional transmission model and involving new packet scheduling models, the overall QoS and bandwidth efficiency are dramatically improved. In non-scalable video streaming system, the maximum video quality gain can be around 5dB compared with the random push method, and the overall uninformative transmiss- sion ratio are reduced to 1% - 2%. In scalable video streaming system, the maximum video quality gain can be around 7dB, and the overall uninformative transmission ratio are reduced to 2% - 3%.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Greg Plaxton. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 93-103).

One of the fundamental challenges in building Peer-to-Peer (P2P) applications is to locate resources across a dynamic set of nodes without centralised servers. Structured overlay networks solve this challenge by proving a key-based routing (KBR) layer that maps keys to nodes. The performance of KBR is strongly influenced by the dynamic and unpredictable conditions of P2P environments. To cope with such conditions a node must maintain its routing state. Routing state maintenance directly influences both lookup latency and bandwidth consumption. The more vigorously that state information is disseminated between nodes, the greater the accuracy and completeness of the routing state and the lower the lookup latency, but the more bandwidth that is consumed. Existing structured P2P overlays provide a set of configuration parameters that can be used to tune the trade-off between lookup latency and bandwidth consumption. However, the scale and complexity of the configuration space makes the overlays difficult to optimise. Further, it is increasingly difficult to design adaptive overlays that can cope with the ever increasing complexity of P2P environments. This thesis is motivated by the vision that adaptive P2P systems of tomorrow, would not only optimise their own parameters, but also generate and adapt their own design. This thesis studies the effects of using an adaptive technique to automatically adapt state dissemination cost and lookup latency in structured overlays under churn. In contrast to previous adaptive approaches, this work investigates the algorithmic adaptation of the fundamental data dissemination protocol rather than tuning the parameter values of a protocol with fixed design. This work illustrates that such a technique can be used to design parameter-free structured overlays that outperform other structured overlays with fixed design such as Chord in terms of lookup latency, bandwidth consumption and lookup correctness. A large amount of experimentation was performed, more than the space allows to report. This thesis presents a set of key findings. The full set of experiments and data is available online at: http://trombone.cs.st-andrews.ac.uk/thesis/analysis.

Information gathered socially online is a key feature of the growth and development of modern society. Presently the Internet is a platform for the distribution of data. Millions of people use Online Social Networks daily as a tool to get updated with social, political, educational or other occurrences. In many cases information derived from an Online Social Network is acted upon and often shared with other networks, without further assessments or judgments. Many people do not check to see if the information shared is credible. A user may trust the information generated by a close friend without questioning its credibility, in contrast to a message generated by an unknown user. This work considers the concept of credibility in the wider sense, by proposing whether a user can trust the service provider or even the information itself. Two key components of credibility have been explored; trustworthiness and expertise. Credibility has been researched in the past using Twitter as a validation tool. The research was focused on automatic methods of assessing the credibility of sets of tweets using analysis of microblog postings related to trending topics to determine the credibility of tweets. This research develops a framework that can assist the assessment of the credibility of messages in Online Social Networks. Four types of credibility are explored (experienced, surface, reputed and presumed credibility) resulting in a credibility hierarchy. To determine the credibility of messages generated and distributed in Online Social Networks, a virtual network is created, which attributes nodes with individual views to generate messages in the network at random, recording data from a network and analysing the data based on the behaviour exhibited by agents (an agent-based modelling approach). The factors considered for the experiment design included; peer-to-peer networking, collaboration, opinion formation and network rewiring. The behaviour of agents, frequency in which messages are shared and used, the pathway of the messages and how this affects credibility of messages is also considered. A framework is designed and the resulting data are tested using the design. The resulting data generated validated the framework in part, supporting an approach whereby the concept of tagging the message status assists the understanding and application of the credibility hierarchy. Validation was carried out with Twitter data acquired through twitter’s Application Programming Interface (API). There were similarities in the generation and frequency of the message distributions in the network; these findings were also recorded and analysed using the framework proposed. Some limitations were encountered while acquiring data from Twitter, however, there was sufficient evidence of correlation between the simulated and real social network datasets to indicate the validity of the framework.

Esta tese tem como objeto de estudo os mecanismos de reputação em comunidades virtuais de aprendizagem implementadas através de redes de compartilhamento Peer-to-Peer. Os sistemas de reputação, modelados através da TIS de Piaget e dos conceitos de comunidade e sociedade apresentados por Ferdinand Tonnies consistem na contribuição desta tese e visam a eficiente implantação de Comunidades Virtuais de Aprendizagem através de Peer-to-Peer. A implementação de Comunidades Virtuais de Aprendizagem através de redes de compartilhamento Peer-to-Peer apresenta diversos aspectos a serem observados. Podemos considerar como fator positivo a popularização do conceito pelo compartilhamento de materiais na Internet, com o aumento do numero de usuários de softwares como o e-mule e o kazaa. Como limitante, temos principalmente a dificuldade de identificação de relevância dos materiais disponibilizados em relação ao contexto de aprendizagem que se pretende estabelecer. Considerando que a identificação de origem e relevância é uma condição indispensável à constituição de Comunidade Virtuais de Aprendizagem, faz-se necessário estabelecer mecanismos de reputação que contemplem tais questões. O conceito de valor, o estabelecimento de critérios de avaliação para os objetos disponibilizados, bem como de classificação dos agentes componentes da comunidade são objetos de estudo da presente tese. Este trabalho situa-se, então, na área de intersecção da Ciência da Computação com as Ciências da Educação e Sociologia. Na área das Ciências da Educação temos o aporte da Teoria de Interação Social de Piaget, da Sociologia buscamos apoio em Tonnies e, visando suportar a comunidade virtual a ser modelada, buscamos o aporte da Ciência da Computação no que diz respeito as redes peer-to-peer. / The main focus of this dissertation is on the reputation mechanisms of virtual learning communities implemented as peer-to-peer content sharing networks. The reputation systems modeled according to the Social Interaction Theory of Piaget and to the concepts of community and society introduced by Ferdinand Tonnies are the main contributions of the present study. The idea is to reach an effective deployment of virtual learning communities through peer-to-peer networks. The implementation of peer-to-peer networks in virtual communities raises several issues that should be noticed. The popularization of this concept due to the increase of content sharing by means of software such as e-mule and kazaa may be considered positive, but there are also limiting factors, as how to identify which material would be relevant for the content in question. Considering that the identification of origin and relevance is a key condition to the constitution of virtual learning communities, it is necessary to establish reputation mechanisms that approach such questions. The concept of value, the establishment of evaluation criteria for objects available, as well as the classification of agents that constitute the community are objects of study of this dissertation. This work takes place in an intersection area among Computer Science, Education and Sociology. The Social Interaction Theory, by Piaget, supports the Education area, Tonnies provides the support for the Sociology issues and, from Computer Science we take the support for the peer-to-peer networks approach.

Esta tese tem como objeto de estudo os mecanismos de reputação em comunidades virtuais de aprendizagem implementadas através de redes de compartilhamento Peer-to-Peer. Os sistemas de reputação, modelados através da TIS de Piaget e dos conceitos de comunidade e sociedade apresentados por Ferdinand Tonnies consistem na contribuição desta tese e visam a eficiente implantação de Comunidades Virtuais de Aprendizagem através de Peer-to-Peer. A implementação de Comunidades Virtuais de Aprendizagem através de redes de compartilhamento Peer-to-Peer apresenta diversos aspectos a serem observados. Podemos considerar como fator positivo a popularização do conceito pelo compartilhamento de materiais na Internet, com o aumento do numero de usuários de softwares como o e-mule e o kazaa. Como limitante, temos principalmente a dificuldade de identificação de relevância dos materiais disponibilizados em relação ao contexto de aprendizagem que se pretende estabelecer. Considerando que a identificação de origem e relevância é uma condição indispensável à constituição de Comunidade Virtuais de Aprendizagem, faz-se necessário estabelecer mecanismos de reputação que contemplem tais questões. O conceito de valor, o estabelecimento de critérios de avaliação para os objetos disponibilizados, bem como de classificação dos agentes componentes da comunidade são objetos de estudo da presente tese. Este trabalho situa-se, então, na área de intersecção da Ciência da Computação com as Ciências da Educação e Sociologia. Na área das Ciências da Educação temos o aporte da Teoria de Interação Social de Piaget, da Sociologia buscamos apoio em Tonnies e, visando suportar a comunidade virtual a ser modelada, buscamos o aporte da Ciência da Computação no que diz respeito as redes peer-to-peer. / The main focus of this dissertation is on the reputation mechanisms of virtual learning communities implemented as peer-to-peer content sharing networks. The reputation systems modeled according to the Social Interaction Theory of Piaget and to the concepts of community and society introduced by Ferdinand Tonnies are the main contributions of the present study. The idea is to reach an effective deployment of virtual learning communities through peer-to-peer networks. The implementation of peer-to-peer networks in virtual communities raises several issues that should be noticed. The popularization of this concept due to the increase of content sharing by means of software such as e-mule and kazaa may be considered positive, but there are also limiting factors, as how to identify which material would be relevant for the content in question. Considering that the identification of origin and relevance is a key condition to the constitution of virtual learning communities, it is necessary to establish reputation mechanisms that approach such questions. The concept of value, the establishment of evaluation criteria for objects available, as well as the classification of agents that constitute the community are objects of study of this dissertation. This work takes place in an intersection area among Computer Science, Education and Sociology. The Social Interaction Theory, by Piaget, supports the Education area, Tonnies provides the support for the Sociology issues and, from Computer Science we take the support for the peer-to-peer networks approach.

Esta tese tem como objeto de estudo os mecanismos de reputação em comunidades virtuais de aprendizagem implementadas através de redes de compartilhamento Peer-to-Peer. Os sistemas de reputação, modelados através da TIS de Piaget e dos conceitos de comunidade e sociedade apresentados por Ferdinand Tonnies consistem na contribuição desta tese e visam a eficiente implantação de Comunidades Virtuais de Aprendizagem através de Peer-to-Peer. A implementação de Comunidades Virtuais de Aprendizagem através de redes de compartilhamento Peer-to-Peer apresenta diversos aspectos a serem observados. Podemos considerar como fator positivo a popularização do conceito pelo compartilhamento de materiais na Internet, com o aumento do numero de usuários de softwares como o e-mule e o kazaa. Como limitante, temos principalmente a dificuldade de identificação de relevância dos materiais disponibilizados em relação ao contexto de aprendizagem que se pretende estabelecer. Considerando que a identificação de origem e relevância é uma condição indispensável à constituição de Comunidade Virtuais de Aprendizagem, faz-se necessário estabelecer mecanismos de reputação que contemplem tais questões. O conceito de valor, o estabelecimento de critérios de avaliação para os objetos disponibilizados, bem como de classificação dos agentes componentes da comunidade são objetos de estudo da presente tese. Este trabalho situa-se, então, na área de intersecção da Ciência da Computação com as Ciências da Educação e Sociologia. Na área das Ciências da Educação temos o aporte da Teoria de Interação Social de Piaget, da Sociologia buscamos apoio em Tonnies e, visando suportar a comunidade virtual a ser modelada, buscamos o aporte da Ciência da Computação no que diz respeito as redes peer-to-peer. / The main focus of this dissertation is on the reputation mechanisms of virtual learning communities implemented as peer-to-peer content sharing networks. The reputation systems modeled according to the Social Interaction Theory of Piaget and to the concepts of community and society introduced by Ferdinand Tonnies are the main contributions of the present study. The idea is to reach an effective deployment of virtual learning communities through peer-to-peer networks. The implementation of peer-to-peer networks in virtual communities raises several issues that should be noticed. The popularization of this concept due to the increase of content sharing by means of software such as e-mule and kazaa may be considered positive, but there are also limiting factors, as how to identify which material would be relevant for the content in question. Considering that the identification of origin and relevance is a key condition to the constitution of virtual learning communities, it is necessary to establish reputation mechanisms that approach such questions. The concept of value, the establishment of evaluation criteria for objects available, as well as the classification of agents that constitute the community are objects of study of this dissertation. This work takes place in an intersection area among Computer Science, Education and Sociology. The Social Interaction Theory, by Piaget, supports the Education area, Tonnies provides the support for the Sociology issues and, from Computer Science we take the support for the peer-to-peer networks approach.