Existe um interesse crescente do mercado por aplicações de multimídia em streaming via rede. Particularmente, as aplicações de live streaming que utilizam a tecnologia de redes P2P para a disseminação de conteúdo têm sido alvo de grande atenção. Aplicações como PPLive e PPStream provam que as aplicações de live streaming em redes P2P são uma realidade com relação à tecnologia atual. Os sistemas de live streaming fornecem um serviço de multicast no nível de aplicação para transmissões ao vivo na Internet. Essas aplicações de live streaming, quando executadas em redes P2P, têm potencial para serem altamente robustas, escaláveis e adaptativas devido à redundância e não dependência de recursos particulares dentre os nodos participantes. Porém, para fazer uso de todas as vantagens disponíveis, a aplicação deve contornar alguns desafios: i) manter a qualidade de playback mesmo com a inerente dinamicidade das redes P2P; ii) impedir que nodos incorretos escondam ações maliciosas atrás do anonimato que existe em P2P; iii) manter a taxa de upload dos nodos participantes da aplicação em um nível aceitável. A taxa de upload dos nodos é muito importante porque a aplicação de live streaming em P2P é uma aplicação cooperativa. Desta forma, esperase que todo novo usuário ajude a aplicação retransmitindo pacotes para outros usuários, mantendo, desta forma, a capacidade global de upload do sistema. Infelizmente, manter a cooperação em live streaming não é uma tarefa trivial, visto que cada nodo enfrenta o dilema social do interesse próprio (individualmente é melhor explorar a cooperação dos outros usuários sem reciprocidade) versus a cooperação para com o grupo. A principal contribuição deste trabalho consiste na apresentação de um modelo matemático baseado em Teoria dos Jogos Evolucionários, cujo objetivo é ajudar a compreender as aplicações de live streaming em redes P2P e os fatores que influenciam o seu correto funcionamento. Como contribuição secundária, este trabalho fornece uma análise estatística do comportamento do download e upload observado nestas aplicações. A análise estatística mostra que existe um decaimento da variância temporal de download e upload nas aplicações de live streaming, e que tal decaimento segue uma lei de potência. Os resultados evolucionários do modelo indicam que, se a queda do índice de satisfação dos usuários com a taxa de download for suave, e se a redução da satisfação devido ao custo de upload for insignificante, então existe um ambiente propício para que a cooperação entre os nodos cresça. De forma inversa, se a queda do índice de satisfação dos usuários com a taxa de download for abrupta, e a redução da satisfação devido ao custo de upload for significativa, então existe um ambiente propício para proliferação de nodos oportunistas. A realização e descrição desta pesquisa é composta de quatro etapas principais: i) a delimitação do cenário de live streaming e a definição do jogo para modelagem; ii) a definição do conjunto de estratégias e da função de utilidade; iii) a criação do modelo; iv) a análise do modelo e a apresentação dos resultados de simulação. A análise do modelo abrange três fases: i) análise estatística e comparação das características de download e upload dos dois simuladores utilizados; ii) avaliação do modelo de Teoria dos Jogos Evolucionários através de simulações; e iii) análise dos resultados evolucionários gerados pelo simulador de Teoria dos Jogos Evolucionários. / There is a growing interest in the market for networked multimedia applications. Live streaming applications that use the technology of P2P networks for distribution of live content have specially been the subject of great attention. Applications such as PPLive and PPStrem demonstrate that P2P live streaming applications are already possible with our present technology. Live streaming systems provide a multicast service in the application level for live broadcasts to users through the Internet. These systems executing in P2P networks have the potential to be highly robust, scalable and adaptive due to the characteristics of these scenarios. However, to take advantage of these potential properties, they must overcome some challenges: i) to maintain the playback quality even with the inherent dynamics of P2P networks; ii) to prevent that incorrect peers hide malicious behavior behind their anonymity; iii) to maintain the upload contribution of peers at acceptable levels. The upload contribution of peers is highly important because live streaming applications are cooperative applications. Therefore, every new user must help the application forwarding packets to other users, thereby maintaining the global upload capacity of the system. Unfortunately, the maintenance of cooperation in live streaming system is not a trivial task, since each node faces the social dilemma of self-interest (individually is always better to explore the cooperation of other users without reciprocity) versus cooperation to the group. The main contribution of this dissertation is the presentation of a mathematical model based on Evolutionary Game Theory, whose goal is to help understanding live streaming P2P applications and the factors that influence their correct operation. As a secondary contribution, this work provides a statistical analysis of download and upload behaviors of peers in live streaming P2P systems. The statistical analysis indicates that there is a decay in the download and upload variances, and that this decay follows a power law. The evolutionary results of the model indicate that, if the satisfaction of users with the download rate is smooth, and the reduction of satisfaction due to the upload cost is negligible, then there is a favorable environment for the growth of cooperation. Conversely, if the satisfaction of users with the download rate is abrupt, and the reduction of satisfaction due to the upload cost is significant, then there is a favorable environment to the proliferation of opportunistic nodes. The realization and description of this research is composed of four main steps: i) the definition of the live streaming scenario and the definition of the game to model this scenario; ii) the definition of the strategy set and of the utility function; iii) the suggestion of a model; iv) the analysis of the proposed model and the presentation of obtained results. The model analysis comprehends three phases: i) the statistical analysis and the comparison of the characteristics of download and upload of the two simulators used in this work; ii) the evaluation of the Evolutionary Game Theory model through simulation; and iii) the analysis of the results generated by the Evolutionary Game Theory simulator.

Landmark-based architecture has been commonly adopted in the networking community as a mechanism to measure and characterize a host's location on the Internet. In most existing landmark based approaches, end hosts use the distance measurements to a common, fixed set of landmarks to derive an estimated location on the Internet. This paper investigates whether it is possible for participating peer nodes in an overlay network to collaboratively construct an accurate geometric model of its topology in a completely decentralized peer-to-peer fashion, without using a fixed set of landmarks. We call such a peer-to-peer approach in topology discovery and modeling using landmarks PALM (Peers As LandMarks). We evaluate the performance characteristics of such a decentralized coordinates-based approach under several factors, including dimensionality of the geometric space, peer distance distribution, and the number of peer-to-peer distance measurements used. We evaluate two PALM-based schemes: RAND-PALM and ISLAND. In RAND-PALM, a peer node randomly selects from existing peer nodes as its landmarks. In ISLAND (Intelligent Selection of Landmarks), each peer node selects its landmarks by exploiting the topological information derived based on existing peer nodes' coordinates values. / Singapore-MIT Alliance (SMA)

Research has shown that late-arriving teen English language learners (ELLs) are deeply rooted in the sociocultural and educational system of their home country for a majority of their schooling time (Duff, 2001; Minichello, 2001). In their transition to a new society in North America, this group encounters sociocultural and linguistic differences in their daily lives. Through a lens entitled Critical Multiple Social Spaces, which combines the Multiple Worlds Model (Phelan et al., 1991), the concept of Third Space (Bhabha, 1994) and a sociocultural perspective on language use (Fairclough, 2001; Pennycook, 2010), this qualitative case study focuses on 10 Chinese ELL adolescents who came to Canada after the age of 15, and examines their cross-trajectory experiences of English practice in their daily lives and their language identities. At the time of this study, they were at the stage of completing high school and applying for admission to higher education institutions. Findings showed that this group’s language use in daily life is full of conflicts, negotiation and consolidation, not only at school as a usual space of contested language practice, but also at home, with peers and in other spaces. At school, social division existed both in and out of class, yet such social division was not merely due to ELLs’ reluctance to integrate. Participants positioned themselves differently in English Literature courses and core classes in accordance with their perceived proficiency. Home, generally regarded as a traditionally stable space of language practice, became another site of complex dynamics. Peer networks also emerged as embodying similar complications. In addition to racial and ethnic factors, age on arrival and length of residence played a significant role in social interaction, impacting both same-ethnic and cross-ethnic peer networks. Based on these findings, four categories are identified pertaining to participants’ cross-trajectory language experiences, in which English spaces are positioned differently in relation to other spaces. Equally noteworthy are the dynamics between social spaces, social relations and language use, which shape – and are shaped by – symbolic power, investment and language identities. The implications of these findings on ELL adolescents’ language use in a broader migration space are also discussed.

Η ανοδική πορεία των Ρ2Ρ δικτύων ήταν το αναπόφευκτο συνεπακόλουθο της ραγδαίας ανάπτυξης του διαδικτύου. Δυστυχώς, τα Ρ2Ρ δίκτυα εξελίχθησαν από χρήσιμα εργαλεία για την εύκολη και γρήγορη διαμοίραση της πληροφορίας, σε δίκτυα που επιτρέπουν τη μη εξουσιοδοτημένη διακίνηση των παράνομων αντιγραφών της πνευματικής ιδιοκτησίας. Για το λόγο αυτό, οι κάτοχοι της πνευματικής ιδιοκτησίας, χρησιμοποιούν ως αμυντικό τους όπλο, για την προστασία τους από τις παραβιάσεις στο copyright της πνευματικής τους ιδιοκτησίας, τις DRM τεχνολογίες, έτσι ώστε να κατορθώνεται ο έλεγχος στη διανομή της πνευματικής ιδιοκτησίας για να μην πέφτει το περιεχόμενο τους σε λάθος χέρια. Οι οπαδοί των Ρ2Ρ δικτύων εμφανίζονται να μην συμφωνούν με την εφαρμογή της DRM τεχνολογίας, η οποία τεχνολογία υποστηρίζει τους κατόχους της πνευματικής ιδιοκτησίας. Τα Ρ2Ρ δίκτυα προσφέρουν πολλές δυνατότητες στους χρήστες, καθώς και στους άλλους συμμετέχοντες στα επιχειρηματικά μοντέλα διανομής περιεχομένου. Για τους λόγους αυτούς, η μελλοντική ύπαρξη των Ρ2Ρ δικτύων θεωρείτε δεδομένη. Επομένως, η ενοποίηση της DRM τεχνολογίας με τις Ρ2Ρ αρχιτεκτονικές είναι αναπόφευκτή, επειδή οι κάτοχοι της πνευματικής ιδιοκτησίας προσπαθούν να διατηρούν τις ισορροπίες, ώστε να συνδυάζουν τη διατήρηση του ελέγχου της πνευματικής ιδιοκτησίας που τους ανήκει, με τη λειτουργικότητα που επιθυμούν οι χρήστες να εμφανίζει το ψηφιακό περιεχόμενο. Στα πλαίσια αυτής της διπλωματικής εργασίας θα μελετήσουμε το ζήτημα της ολοκλήρωσης των Ρ2Ρ δικτύων μέσω της τεχνολογίας των DRM συστημάτων. Στο πρώτο κεφάλαιο της εργασίας μας, θα αναφερθούμε γενικά στο τι είναι η DRM τεχνολογία, για ποιο λόγο είναι σημαντική η εφαρμογή της τεχνολογίας αυτής στα ψηφιακά δεδομένα, ποιους περιορισμούς θέτει στους χρήστες και ποια μειονεκτήματα εμφανίζει. Στη συνέχει του κεφαλαίου, θα παρουσιάσουμε μια αναλυτική μελέτη της έννοιας του Digital Rights Management, των τεχνολογιών που σχετίζονται με την έννοια αυτή και θα γίνει μελέτη της μορφής που εμφανίζουν τα υπάρχοντα DRM συστήματα. Αρχικά, παρουσιάσουμε τους ορισμούς που σχετίζονται με την έννοια του DRM, καθώς και τις υπάρχουσες όψεις. Έπειτα, παραθέτουμε τις υπάρχουσες DRM τεχνολογίες, καθώς και τις ελλείψεις που παρουσιάζουνε οι τεχνολογίες αυτές. Στη συνέχεια, παρουσιάζουμε περιληπτικά ένα τυπικό DRM σύστημα και αναφερόμαστε στις απαιτήσεις και στα συστατικά στοιχεία ενός τέτοιου συστήματος. Επίσης, κάνουμε μια μικρή αναφορά στους τύπους των επιθέσεων που αντιμετωπίσουν συνήθως τα DRM συστήματα. Στο δεύτερο κεφάλαιο της εργασίας μας μελετάμε την έννοια Ρ2Ρ και αναφερόμαστε στην τεχνολογία των Ρ2Ρ δικτύων. Στο πρώτο μέρος του κεφαλαίου, θα ασχοληθούμε με την περιγραφή των Ρ2Ρ δικτύων. Θα αναφερθούμε στη δομή τους, στις κατηγοριοποιήσεις τους, καθώς και στα πλεονεκτήματα που εμφανίζουν. Στο δεύτερο μέρος του κεφαλαίου, ασχολούμαστε με την οικονομία των Ρ2Ρ δικτύων. Αρχικά, μελετάμε κάποιες σημαντικές Ρ2Ρ αρχιτεκτονικές και εφαρμογές, ενώ στη συνέχεια τονίζουμε τα οικονομικά χαρακτηριστικά που εμφανίζουν τα δίκτυα αυτά και τα συγκρίνουμε με τα όμοια χαρακτηριστικά που εμφανίζονται στη βιβλιογραφία της οικονομίας. Στο τρίτο μέρος του κεφαλαίου, συζητάμε τους κινδύνους που αντιμετωπίζουν οι προμηθευτές περιεχομένου και τις επιχειρηματικές ευκαιρίες που προκύπτουν από τα μοντέλα των Ρ2Ρ υπηρεσιών. Προτείνονται κάποιοι μηχανισμοί, οι οποίοι δίνουν κίνητρα συμμετοχής για το μετριασμό των κινδύνων που προκύπτουν από το free-riding και για τη βελτίωση της συνολικής οικονομικής δραστηριότητας των Ρ2Ρ υπηρεσιών συναλλαγής και περιγράφουμε σε γενικές γραμμές πως αυτό μπορεί να εφαρμοστεί ως χαρακτηριστικό του λογισμικού στα Ρ2Ρ συστήματα εφαρμογών. Εξετάζουμε επίσης, το ρόλο που παίζουν οι ενδιάμεσοι στα Ρ2Ρ συστήματα και τελειώνουμε το κεφάλαιο με την περιγραφή ενός μοντέλου τριών επιπέδων, το οποίο περιγράφει τις Ρ2Ρ υπηρεσίες στο επίπεδο των τεχνολογικών εφαρμογών, στο επίπεδο των εφαρμογών της κοινότητας και τέλος, στο επίπεδο των επιχειρηματικών εφαρμογών. Στο τρίτο κεφάλαιο της διπλωματικής, επεξηγείται το κίνητρο για την αναπόφευκτη κατάσταση της ενοποίησης της DRM τεχνολογίας με τις αρχιτεκτονικές των Ρ2Ρ δικτύων. Μετά από τη σύντομη ανασκόπηση που θα κάνουμε για το πώς απέκτησαν ύπαρξη τα DRM συστήματα και τα Ρ2Ρ δίκτυα, επεξηγούμε τις ανάγκες που δημιούργησαν και τις ευκαιρίες που οδήγησαν στην ανάπτυξη της διαδικασίας ενοποίησης της λειτουργικότητας των DRM συστημάτων με τα Ρ2Ρ δίκτυα. Στη συνέχεια, συζητάμε τα χαρακτηριστικά της DRM τεχνολογίας, τα οποία καθιστούν την τεχνολογία αυτή εξαιρετικά κατάλληλη για την ενοποίηση της με τα Ρ2Ρ δίκτυα, και συνοψίζουμε με τις ελλείψεις που εμφανίζουν πολλές από τις υπάρχουσες DRM επιλύσεις, εκτιμώντας και τα χαρακτηριστικά που αυτές εμφανίζουν. Τέλος, στο τελευταίο μέρος του κεφαλαίου μελετάμε κάποιες υπάρχουσες μελέτες για αρχιτεκτονικές συστημάτων, τα οποία συστήματα προσπαθούν να ενοποιήσουν τις εφαρμογές των DRM συστημάτων με τις τεχνολογίες των Ρ2Ρ δικτύων. Για την κάθε αρχιτεκτονική συστήματος παρουσιάζουμε μια αναλυτική μελέτη των τεχνολογιών που χρησιμοποιεί και των συστημάτων που εφαρμόζει. Τέλος, στα πλαίσια της διπλωματικής θα προσπαθήσουμε να υλοποιήσουμε ένα σύστημα το οποίο θα παρουσιάζει τα DRM συστήματα και τα Ρ2Ρ δίκτυα ως συμπληρωματικές τεχνολογίες. Πιο συγκεκριμένα, προτείνεται μια Ρ2Ρ υποδομή, η οποία επιτρέπει την ευρεία ανταλλαγή του ψηφιακού περιεχομένου, ενώ παράλληλα υποστηρίζει την προστασία του copyright και τη διαχείριση του διαμέσου των DRM τεχνολογιών. Η προστασία του ψηφιακού περιεχομένου θα πραγματοποιείται με τον έλεγχο στη πρόσβαση και τη χρησιμοποίηση των τεχνολογιών κρυπτογράφησης και ψηφιακής υδατοσήμανσης για τα υπό προστασία πνευματικά δεδομένα. / The ascendant course of P2P networks were the inevitable consequence of rapid growth of the internet. Unfortunately, the P2P networks were evolved by useful tools for the easy and fast distribution of information, in networks that allow the not permitted distribution of illegal copies of intellectual property. For this reason, the holders of intellectual property, use as their defensive arm, for their protection from the violations in the copyright of their intellectual property, the DRM technologies, so as to is achieved the control in the distribution of intellectual property in order to not fall their content in error hands. The partisans of P2P networks present itself to not agree with the application of DRM technology, which supports the holders of intellectual property. The P2P networks offer a lot of possibilities in the users, as well as in the other participating in the enterprising models for the distribution of the content. For this reasons, the future existence of P2P networks considering given. Consequently, the integration of DRM technology with the P2P architectures is inevitable, because the holders of intellectual property try to maintain the balances, so that they combine the maintenance of control of intellectual property that belongs to them, with the functionality that wish the users to present the digital content. In the frames of this diplomatic work, we will study the question of completion of P2P networks via the technology of DRM systems. In the first chapter of our work, we will be reported, as generally speaking, in what is the DRM technology, for who reason is important the application of this technology in the digital data, who restrictions it places in the users and what disadvantages it presents. Then, we will present an analytic study of significance of Digital Rights Management, the technologies that are related with this significance and will become study of form that presents the existing DRM systems. Initially, we present the definitions that are related with the significance of DRM, as well as the existing aspects. Then, we mention the existing DRM technologies, as well as the lack of these technologies. Afterwards, we present a formal DRM system and then, we report the requirements and the constitutive elements of such system. Also, we make a small report in the types of attacks that face usually the DRM systems. In the second chapter of our work, we study the significance of P2P and report the technology of P2P networks. In the first part of chapter, we will deal with the description of P2P of networks. We will be reported in their structure, in their classifications, as well as in the advantages that they present. In the second part, we dealt with the economy of P2P networks. Initially, we study certain important P2P architectures and applications, while afterwards we stress the economic characteristics that present these networks and compare these characteristics with the similar characteristics that are presented in the bibliography of economy. In the third part, we discuss the dangers that face the suppliers of content and the enterprising occasions that result from the models of P2P services. Are proposed certain mechanisms, which give motives of attendance for the mitigation of dangers that results from the free-riding and for improvement of total economic activity of P2P services of transaction and describes in general lines that this can be applied as characteristic of software in the applications of P2P systems. We examine also, the role that play the intermediary in the P2P systems and we finish the chapter with the description of a three-levels model, which describes the P2P services in the level of technological applications, in the level of applications of community and finally, in the level of enterprising applications. In the third chapter of diplomatic, is explained the motive for the inevitable situation of integrating DRM technology with the architecture of P2P networks. After the short examination that we will make for how acquired existence the DRM systems and the P2P networks, we explain the needs that created and the occasions that led to the growth of process of integrating the functionality of DRM systems with the P2P networks. Afterwards, we discuss the characteristics of DRM technology, which render this technology exceptionally suitable for integration with P2P networks, and we conclude with the lacks that present many from the existing DRM resolutions, appreciating and the characteristics that these present. Finally, in the last part of chapter we study some existing studies on architecture systems, which systems try to integrate the applications of DRM systems with the technologies of P2P networks. For each architecture system we present an analytic study of technologies that it uses and the systems that it applies. Finally, in the frames of diplomatic we will try to implement a system which will present the DRM systems and P2P networks as complementary technologies. More concretely, is proposed a P2P infrastructure, which allows the wide exchange of digital content, while at the same time supports the protection of the copyright and the management of digital content through the DRM technology. The protection of digital content will be realized with access control and utilization of encryption and digital watermarking technologies for the protected intellectual data.

Research has shown that late-arriving teen English language learners (ELLs) are deeply rooted in the sociocultural and educational system of their home country for a majority of their schooling time (Duff, 2001; Minichello, 2001). In their transition to a new society in North America, this group encounters sociocultural and linguistic differences in their daily lives. Through a lens entitled Critical Multiple Social Spaces, which combines the Multiple Worlds Model (Phelan et al., 1991), the concept of Third Space (Bhabha, 1994) and a sociocultural perspective on language use (Fairclough, 2001; Pennycook, 2010), this qualitative case study focuses on 10 Chinese ELL adolescents who came to Canada after the age of 15, and examines their cross-trajectory experiences of English practice in their daily lives and their language identities. At the time of this study, they were at the stage of completing high school and applying for admission to higher education institutions. Findings showed that this group’s language use in daily life is full of conflicts, negotiation and consolidation, not only at school as a usual space of contested language practice, but also at home, with peers and in other spaces. At school, social division existed both in and out of class, yet such social division was not merely due to ELLs’ reluctance to integrate. Participants positioned themselves differently in English Literature courses and core classes in accordance with their perceived proficiency. Home, generally regarded as a traditionally stable space of language practice, became another site of complex dynamics. Peer networks also emerged as embodying similar complications. In addition to racial and ethnic factors, age on arrival and length of residence played a significant role in social interaction, impacting both same-ethnic and cross-ethnic peer networks. Based on these findings, four categories are identified pertaining to participants’ cross-trajectory language experiences, in which English spaces are positioned differently in relation to other spaces. Equally noteworthy are the dynamics between social spaces, social relations and language use, which shape – and are shaped by – symbolic power, investment and language identities. The implications of these findings on ELL adolescents’ language use in a broader migration space are also discussed.

In the past few years, we have witnessed the continuous growth in popularity of delay-sensitive applications. Applications like live video streaming, multimedia conferencing, VoIP and online gaming account for a major part of Internet traffic these days. It is also predicted that this trend will continue in the coming years. This emphasizes the significance of developing efficient scheduling algorithms in communication networks with guaranteed low delay performance. In our work, we try to address the delay issue in some major instances of wireless communication networks. First, we study a wireless content distribution network (CDN), in which the requests for the content may have service deadlines. Our wireless CDN consists of a media vault that hosts all the content in the system and a number of local servers (base stations), each having a cache for temporarily storing a subset of the content. There are two major questions associated with this framework: (i) content caching: which content should be loaded in each cache? and (ii) wireless network scheduling: how to appropriately schedule the transmissions from wireless servers? Using ideas from queuing theory, we develop provably optimal algorithms to jointly solve the caching and scheduling problems. Next, we focus on wireless relay networks. It is well accepted that network coding can enhance the performance of these networks by exploiting the broadcast nature of the wireless medium. This improvement is usually evaluated in terms of the number of required transmissions for delivering flow packets to their destinations. In this work, we study the effect of delay on the performance of network coding by characterizing a trade-off between latency and the performance gain achieved by employing network coding. More specifically, we associate a holding cost for delaying packets before delivery and a transmission cost for each broadcast transmission made by the relay node. Using a Markov decision process (MDP) argument, we prove a simple threshold-based policy is optimal in the sense of minimum long-run average cost. Finally, we analyze delay-sensitive applications in wireless peer-to-peer (P2P) networks. We consider a hybrid network which consists of (i) an expensive base station-to-peer (B2P) network with unicast transmissions, and (ii) a free broadcast P2P network. In such a framework, we study two popular applications: (a) a content distribution application with service deadlines, and (b) a multimedia live streaming application. In both problems, we utilize random linear network coding over finite fields to simplify the coordination of the transmissions. For these applications, we provide efficient algorithms to schedule the transmissions such that some quality of service (QoS) requirements are satisfied with the minimum cost of B2P usage. The algorithms are proven to be throughput optimal for sufficiently large field sizes and perform reasonably well for finite fields.

Existe um interesse crescente do mercado por aplicações de multimídia em streaming via rede. Particularmente, as aplicações de live streaming que utilizam a tecnologia de redes P2P para a disseminação de conteúdo têm sido alvo de grande atenção. Aplicações como PPLive e PPStream provam que as aplicações de live streaming em redes P2P são uma realidade com relação à tecnologia atual. Os sistemas de live streaming fornecem um serviço de multicast no nível de aplicação para transmissões ao vivo na Internet. Essas aplicações de live streaming, quando executadas em redes P2P, têm potencial para serem altamente robustas, escaláveis e adaptativas devido à redundância e não dependência de recursos particulares dentre os nodos participantes. Porém, para fazer uso de todas as vantagens disponíveis, a aplicação deve contornar alguns desafios: i) manter a qualidade de playback mesmo com a inerente dinamicidade das redes P2P; ii) impedir que nodos incorretos escondam ações maliciosas atrás do anonimato que existe em P2P; iii) manter a taxa de upload dos nodos participantes da aplicação em um nível aceitável. A taxa de upload dos nodos é muito importante porque a aplicação de live streaming em P2P é uma aplicação cooperativa. Desta forma, esperase que todo novo usuário ajude a aplicação retransmitindo pacotes para outros usuários, mantendo, desta forma, a capacidade global de upload do sistema. Infelizmente, manter a cooperação em live streaming não é uma tarefa trivial, visto que cada nodo enfrenta o dilema social do interesse próprio (individualmente é melhor explorar a cooperação dos outros usuários sem reciprocidade) versus a cooperação para com o grupo. A principal contribuição deste trabalho consiste na apresentação de um modelo matemático baseado em Teoria dos Jogos Evolucionários, cujo objetivo é ajudar a compreender as aplicações de live streaming em redes P2P e os fatores que influenciam o seu correto funcionamento. Como contribuição secundária, este trabalho fornece uma análise estatística do comportamento do download e upload observado nestas aplicações. A análise estatística mostra que existe um decaimento da variância temporal de download e upload nas aplicações de live streaming, e que tal decaimento segue uma lei de potência. Os resultados evolucionários do modelo indicam que, se a queda do índice de satisfação dos usuários com a taxa de download for suave, e se a redução da satisfação devido ao custo de upload for insignificante, então existe um ambiente propício para que a cooperação entre os nodos cresça. De forma inversa, se a queda do índice de satisfação dos usuários com a taxa de download for abrupta, e a redução da satisfação devido ao custo de upload for significativa, então existe um ambiente propício para proliferação de nodos oportunistas. A realização e descrição desta pesquisa é composta de quatro etapas principais: i) a delimitação do cenário de live streaming e a definição do jogo para modelagem; ii) a definição do conjunto de estratégias e da função de utilidade; iii) a criação do modelo; iv) a análise do modelo e a apresentação dos resultados de simulação. A análise do modelo abrange três fases: i) análise estatística e comparação das características de download e upload dos dois simuladores utilizados; ii) avaliação do modelo de Teoria dos Jogos Evolucionários através de simulações; e iii) análise dos resultados evolucionários gerados pelo simulador de Teoria dos Jogos Evolucionários. / There is a growing interest in the market for networked multimedia applications. Live streaming applications that use the technology of P2P networks for distribution of live content have specially been the subject of great attention. Applications such as PPLive and PPStrem demonstrate that P2P live streaming applications are already possible with our present technology. Live streaming systems provide a multicast service in the application level for live broadcasts to users through the Internet. These systems executing in P2P networks have the potential to be highly robust, scalable and adaptive due to the characteristics of these scenarios. However, to take advantage of these potential properties, they must overcome some challenges: i) to maintain the playback quality even with the inherent dynamics of P2P networks; ii) to prevent that incorrect peers hide malicious behavior behind their anonymity; iii) to maintain the upload contribution of peers at acceptable levels. The upload contribution of peers is highly important because live streaming applications are cooperative applications. Therefore, every new user must help the application forwarding packets to other users, thereby maintaining the global upload capacity of the system. Unfortunately, the maintenance of cooperation in live streaming system is not a trivial task, since each node faces the social dilemma of self-interest (individually is always better to explore the cooperation of other users without reciprocity) versus cooperation to the group. The main contribution of this dissertation is the presentation of a mathematical model based on Evolutionary Game Theory, whose goal is to help understanding live streaming P2P applications and the factors that influence their correct operation. As a secondary contribution, this work provides a statistical analysis of download and upload behaviors of peers in live streaming P2P systems. The statistical analysis indicates that there is a decay in the download and upload variances, and that this decay follows a power law. The evolutionary results of the model indicate that, if the satisfaction of users with the download rate is smooth, and the reduction of satisfaction due to the upload cost is negligible, then there is a favorable environment for the growth of cooperation. Conversely, if the satisfaction of users with the download rate is abrupt, and the reduction of satisfaction due to the upload cost is significant, then there is a favorable environment to the proliferation of opportunistic nodes. The realization and description of this research is composed of four main steps: i) the definition of the live streaming scenario and the definition of the game to model this scenario; ii) the definition of the strategy set and of the utility function; iii) the suggestion of a model; iv) the analysis of the proposed model and the presentation of obtained results. The model analysis comprehends three phases: i) the statistical analysis and the comparison of the characteristics of download and upload of the two simulators used in this work; ii) the evaluation of the Evolutionary Game Theory model through simulation; and iii) the analysis of the results generated by the Evolutionary Game Theory simulator.

Sistemas corporativos modernos cada vez mais dependentes da rede e a integração de serviços entorno do modelo TCP/IP elevam a exigência de Qualidade de Serviço da infraestrutura de TI. Neste cenário, o dinamismo das redes atuais em conjunto com os novos requisitos de QoS exigem que a infra-estrutura de TI seja mais autônoma e confiável. Para tratar esta questão, o modelo de Gerenciamento de Redes Baseado em Políticas, proposto pelo IETF, vem se consolidando como uma abordagem para controlar o comportamento da rede através do controle das configurações dos seus dispositivos. Porém, o foco deste modelo é o gerenciamento de políticas internas a um domínio administrativo. Esta característica faz com que o modelo possua algumas limitações, tais como a incapacidade de estabelecer qualquer tipo de coordenação entre diferentes PDPs e a impossibilidade de reagir a eventos externos. Visando agregar autonomia ao modelo de gerenciamento baseado em políticas, este trabalho propõe uma arquitetura em camadas que empregue os conceitos de Autonomic Computing relacionados a: i) adaptação dinâmica dos recursos gerenciados em resposta às mudanças no ambiente, ii) integração com sistemas de gerenciamento de outros domínios através do recebimento de notificações destes, iii) capacidade de planejar ações de gerenciamento e iv) promoção de ações de gerenciamento que envolvam mais de um domínio administrativo, estabelecendo uma espécie de coordenação entre PDPs. Para a implementação destes conceitos, a arquitetura prevê o uso de uma camada peerto- peer (P2P) sobre a plataforma de políticas. Desta forma, a partir de uma notificação recebida, a camada P2P planeja ações visando adaptar o comportamento da rede aos eventos ocorridos na infra-estrutura de TI. As ações planejadas traduzem-se em inclusões ou remoções de políticas da plataforma de políticas responsável por gerenciar a configuração dos dispositivos de rede. Para notificações que envolvam recursos de mais de um domínio administrativo, os peers de gerenciamento agem de forma coordenada para implantar as devidas ações em cada domínio. A arquitetura proposta foi projetada com foco em prover QoS em uma rede com suporte à DiffServ, embora acredite-se que a sua estrutura seja genérica o bastante para ser aplicada a outros contextos. Como estudo de caso, foi analisado o emprego da arquitetura em resposta a eventos gerados por uma grade computacional. Foi elaborado ainda um protótipo da arquitetura utilizando o Globus Toolkit 4 como fonte de eventos. / Modern corporative systems becoming more dependent of the network and the integration of services around the TCP/IP model increase the requirement of Quality of Service (QoS) of the IT infrastructure. In this scene, the dynamism of current networks together with the new requirements of QoS demands a more autonomous and reliable IT infrastructure. To address this issue, the model of Police Based Network Management, proposed by IETF, has been consolidated as an approach to control the behavior of the network through the control of the configurations of its devices. However, the focus of this model is the management of the policies internal to an administrative domain. This feature brings some limitations to the model, such as the incapacity to establish any kind of coordination between different PDPs and the impossibility to react to external events. Aiming at to add autonomy to the model of Policy Based Network Management, this work proposes a layered architecture based on the concepts of Autonomic Computing related to: i) the dynamic adaptation of the managed resources in response to changes in the environment, ii) integration with management systems of other domains through the reception of notifications of these systems, iii) ability of planning the management actions and iv) execution of multi-domain management actions, establishing a kind of coordination between PDPs. To implement these concepts, the architecture was designed with a peer-to-peer layer above the policy platform. Thus, from a received notification, the P2P layer plans actions aiming to adapt the network behavior in response to the events occurred in the IT infrastructure. The planned actions are, actually, inclusions or removals of policies in the policy platform responsible for the management of the network devices configuration. For notifications related with resources of more than one administrative domain, the management peers act in a coordinated way in order to establish the suitable actions in each domain. The proposed architecture was designed with focus in providing QoS in a network with support to DiffServ, although we believe that its structure is generic enough to be applied to other contexts. As case study, it was analyzed the use of the architecture in response to events generated by a computational grid. Additionally, a prototype of the architecture was build making use of Globus Toolkit 4 as an event source.

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.

Sistemas corporativos modernos cada vez mais dependentes da rede e a integração de serviços entorno do modelo TCP/IP elevam a exigência de Qualidade de Serviço da infraestrutura de TI. Neste cenário, o dinamismo das redes atuais em conjunto com os novos requisitos de QoS exigem que a infra-estrutura de TI seja mais autônoma e confiável. Para tratar esta questão, o modelo de Gerenciamento de Redes Baseado em Políticas, proposto pelo IETF, vem se consolidando como uma abordagem para controlar o comportamento da rede através do controle das configurações dos seus dispositivos. Porém, o foco deste modelo é o gerenciamento de políticas internas a um domínio administrativo. Esta característica faz com que o modelo possua algumas limitações, tais como a incapacidade de estabelecer qualquer tipo de coordenação entre diferentes PDPs e a impossibilidade de reagir a eventos externos. Visando agregar autonomia ao modelo de gerenciamento baseado em políticas, este trabalho propõe uma arquitetura em camadas que empregue os conceitos de Autonomic Computing relacionados a: i) adaptação dinâmica dos recursos gerenciados em resposta às mudanças no ambiente, ii) integração com sistemas de gerenciamento de outros domínios através do recebimento de notificações destes, iii) capacidade de planejar ações de gerenciamento e iv) promoção de ações de gerenciamento que envolvam mais de um domínio administrativo, estabelecendo uma espécie de coordenação entre PDPs. Para a implementação destes conceitos, a arquitetura prevê o uso de uma camada peerto- peer (P2P) sobre a plataforma de políticas. Desta forma, a partir de uma notificação recebida, a camada P2P planeja ações visando adaptar o comportamento da rede aos eventos ocorridos na infra-estrutura de TI. As ações planejadas traduzem-se em inclusões ou remoções de políticas da plataforma de políticas responsável por gerenciar a configuração dos dispositivos de rede. Para notificações que envolvam recursos de mais de um domínio administrativo, os peers de gerenciamento agem de forma coordenada para implantar as devidas ações em cada domínio. A arquitetura proposta foi projetada com foco em prover QoS em uma rede com suporte à DiffServ, embora acredite-se que a sua estrutura seja genérica o bastante para ser aplicada a outros contextos. Como estudo de caso, foi analisado o emprego da arquitetura em resposta a eventos gerados por uma grade computacional. Foi elaborado ainda um protótipo da arquitetura utilizando o Globus Toolkit 4 como fonte de eventos. / Modern corporative systems becoming more dependent of the network and the integration of services around the TCP/IP model increase the requirement of Quality of Service (QoS) of the IT infrastructure. In this scene, the dynamism of current networks together with the new requirements of QoS demands a more autonomous and reliable IT infrastructure. To address this issue, the model of Police Based Network Management, proposed by IETF, has been consolidated as an approach to control the behavior of the network through the control of the configurations of its devices. However, the focus of this model is the management of the policies internal to an administrative domain. This feature brings some limitations to the model, such as the incapacity to establish any kind of coordination between different PDPs and the impossibility to react to external events. Aiming at to add autonomy to the model of Policy Based Network Management, this work proposes a layered architecture based on the concepts of Autonomic Computing related to: i) the dynamic adaptation of the managed resources in response to changes in the environment, ii) integration with management systems of other domains through the reception of notifications of these systems, iii) ability of planning the management actions and iv) execution of multi-domain management actions, establishing a kind of coordination between PDPs. To implement these concepts, the architecture was designed with a peer-to-peer layer above the policy platform. Thus, from a received notification, the P2P layer plans actions aiming to adapt the network behavior in response to the events occurred in the IT infrastructure. The planned actions are, actually, inclusions or removals of policies in the policy platform responsible for the management of the network devices configuration. For notifications related with resources of more than one administrative domain, the management peers act in a coordinated way in order to establish the suitable actions in each domain. The proposed architecture was designed with focus in providing QoS in a network with support to DiffServ, although we believe that its structure is generic enough to be applied to other contexts. As case study, it was analyzed the use of the architecture in response to events generated by a computational grid. Additionally, a prototype of the architecture was build making use of Globus Toolkit 4 as an event source.