Com o aumento da concorrência sofrido pelas operadoras de telecomunicações frente à entrada de diversas empresas de outros ramos no mercado de comunicação, como, por exemplo, os Provedores de Serviço de Internet (ISPs - Internet Service Providers) através da oferta de serviços de voz sobre IP, tais operadoras viram-se obrigadas a diversificar sua oferta de serviços para gerar novas fontes de receita. Por possuírem ampla infra-estrutura instalada, as operadoras de telecomunicações passaram a oferecer, também, serviço de TV aos usuários, através de suas redes (convergentes) de telefonia e dados já existentes, o chamado IPTV. O objetivo deste trabalho foi possibilitar, neste cenário, que estas empresas consigam oferecer, além dos serviços convencionais de TV (e.g., transmissões lineares dos conteúdos nos canais de TV), serviços diferenciados empregando-se a mesma infra-estrutura. O foco deste trabalho é a oferta do serviço de apresentação deslocada no tempo dos conteúdos transmitidos linearmente nos canais de TV, sem a necessidade de configuração prévia por parte do usuário. Desta maneira, dá-se maior flexibilidade ao usuário, possibilitando-o assistir aos conteúdos que lhe interessam, no horário mais conveniente, sem ter que se preocupar com isso antecipadamente (i.e., sem a necessidade de configurar algum equipamento para gravar o conteúdo ou saber antecipadamente quais programas lhe interessam). Para isso foram pesquisadas e analisadas tanto tecnologias de transmissão e distribuição de conteúdos, como também o paradigma peer-to-peer, muito utilizado atualmente no compartilhamento de arquivos na Internet. A partir daí, foi concebida uma arquitetura capaz de oferecer tanto o serviço tradicional de transmissão linear de TV, quanto de apresentar vídeos deslocados no tempo (i.e., vídeos cuja transmissão linear já foi iniciada ou até concluída, a partir de qualquer posição já transmitida), combinando-se técnicas de multidifusão de dados, armazenamento distribuído e protocolos peer-to-peer. Desta maneira, obteve-se uma solução eficiente, utilizando-se os recursos disponíveis em todo o sistema, incluindo recursos ociosos dos usuários finais, para auxiliar no armazenamento e distribuição dos conteúdos deslocados no tempo. Finalmente, um protótipo foi desenvolvido como prova de conceito da arquitetura proposta neste trabalho, e, juntamente com os testes realizados, comprovam a viabilidade de se utilizar redes P2P para a distribuição dos conteúdos para a apresentação deslocada no tempo. / Telecommunication companies are suffering from the increasing offer of cheap and reliable voice over IP services, being forced to diversify their services looking for new revenue possibilities. Since these companies have a vast infrastructure, they are now providing TV services through the same telephony and data infrastructure, using their IP networks to offer IPTV. The goal of the present work is to allow, in this scenario, that such companies offer, additionally to the traditional TV services (e.g., the linear transmissions of the TV channels), differentiated services through the same infrastructure. The focus of the present work is, therefore, the offering of the time-shift service, allowing users to watch linear transmitted contents, time-shifted, without the need for any in-advance configuration. This approach gives more flexibility to the users, allowing them to choose the most appropriate time to watch some content without having to specify their interests in advance (i.e., without configuring some equipment to record the content or knowing in advance which programs will interest themselves). To achieve this goal, technologies for content transmission and distribution, as well as the peer-to-peer paradigm for file sharing were studied, resulting in the development of an architecture capable of offering the traditional linear transmissions service as well as the possibility of time-shift, combining multicast, distributed caching and peer-to-peer technologies. Accordingly, an efficient solution was envisioned, making use of all available resources in the system, including idle resources in the user equipments, to help in the caching and distribution of the time-shifted contents. Finally, a prototype was developed as a proof-of-concept for the designed architecture, which together with the performed tests, shows the viability of utilizing P2P networks in the distribution of time-shifted contents.

Com o aumento da concorrência sofrido pelas operadoras de telecomunicações frente à entrada de diversas empresas de outros ramos no mercado de comunicação, como, por exemplo, os Provedores de Serviço de Internet (ISPs - Internet Service Providers) através da oferta de serviços de voz sobre IP, tais operadoras viram-se obrigadas a diversificar sua oferta de serviços para gerar novas fontes de receita. Por possuírem ampla infra-estrutura instalada, as operadoras de telecomunicações passaram a oferecer, também, serviço de TV aos usuários, através de suas redes (convergentes) de telefonia e dados já existentes, o chamado IPTV. O objetivo deste trabalho foi possibilitar, neste cenário, que estas empresas consigam oferecer, além dos serviços convencionais de TV (e.g., transmissões lineares dos conteúdos nos canais de TV), serviços diferenciados empregando-se a mesma infra-estrutura. O foco deste trabalho é a oferta do serviço de apresentação deslocada no tempo dos conteúdos transmitidos linearmente nos canais de TV, sem a necessidade de configuração prévia por parte do usuário. Desta maneira, dá-se maior flexibilidade ao usuário, possibilitando-o assistir aos conteúdos que lhe interessam, no horário mais conveniente, sem ter que se preocupar com isso antecipadamente (i.e., sem a necessidade de configurar algum equipamento para gravar o conteúdo ou saber antecipadamente quais programas lhe interessam). Para isso foram pesquisadas e analisadas tanto tecnologias de transmissão e distribuição de conteúdos, como também o paradigma peer-to-peer, muito utilizado atualmente no compartilhamento de arquivos na Internet. A partir daí, foi concebida uma arquitetura capaz de oferecer tanto o serviço tradicional de transmissão linear de TV, quanto de apresentar vídeos deslocados no tempo (i.e., vídeos cuja transmissão linear já foi iniciada ou até concluída, a partir de qualquer posição já transmitida), combinando-se técnicas de multidifusão de dados, armazenamento distribuído e protocolos peer-to-peer. Desta maneira, obteve-se uma solução eficiente, utilizando-se os recursos disponíveis em todo o sistema, incluindo recursos ociosos dos usuários finais, para auxiliar no armazenamento e distribuição dos conteúdos deslocados no tempo. Finalmente, um protótipo foi desenvolvido como prova de conceito da arquitetura proposta neste trabalho, e, juntamente com os testes realizados, comprovam a viabilidade de se utilizar redes P2P para a distribuição dos conteúdos para a apresentação deslocada no tempo. / Telecommunication companies are suffering from the increasing offer of cheap and reliable voice over IP services, being forced to diversify their services looking for new revenue possibilities. Since these companies have a vast infrastructure, they are now providing TV services through the same telephony and data infrastructure, using their IP networks to offer IPTV. The goal of the present work is to allow, in this scenario, that such companies offer, additionally to the traditional TV services (e.g., the linear transmissions of the TV channels), differentiated services through the same infrastructure. The focus of the present work is, therefore, the offering of the time-shift service, allowing users to watch linear transmitted contents, time-shifted, without the need for any in-advance configuration. This approach gives more flexibility to the users, allowing them to choose the most appropriate time to watch some content without having to specify their interests in advance (i.e., without configuring some equipment to record the content or knowing in advance which programs will interest themselves). To achieve this goal, technologies for content transmission and distribution, as well as the peer-to-peer paradigm for file sharing were studied, resulting in the development of an architecture capable of offering the traditional linear transmissions service as well as the possibility of time-shift, combining multicast, distributed caching and peer-to-peer technologies. Accordingly, an efficient solution was envisioned, making use of all available resources in the system, including idle resources in the user equipments, to help in the caching and distribution of the time-shifted contents. Finally, a prototype was developed as a proof-of-concept for the designed architecture, which together with the performed tests, shows the viability of utilizing P2P networks in the distribution of time-shifted contents.

This PhD thesis treats some problems concerning nonlinear differential equations. In the first two papers computer-assisted proofs are used. The differential equations there are rewritten as fixed point problems, and the existence of solutions are proved. The problem in the first paper is one-dimensional; with one boundary condition given by an integral. The problem in the second paper is three-dimensional, and Dirichlet boundary conditions are used. Both problems have their origins in fluid dynamics. Paper III describes an inverse problem for the heat equation. Given the solution, a solution dependent diffusion coefficient is estimated by intervals at a finite set of points. The method includes the construction of set-valued level curves and two-dimensional splines. In paper IV we prove that there exists a unique, globally attracting fixed point for a differential equation system. The differential equation system arises as the number of peers in a peer-to-peer network, which is described by a suitably scaled Markov chain, goes to infinity. In the proof linearization and Dulac's criterion are used.

Today’s technology of music file sharing in peer-to-peer networks is genius. Peer-to-peer are networks composed of several computers enabling files to be shared among users. A substantial part of the files shared constitute unlawful copies; uploading and downloading of such files infringes copyright legislation. File sharing through peer-to-peer networks is therefore both a genius technology and a copyright infringement. Peer-to-peer technology has been subject to heavy debate in media, both nationally and internationally. The issue of illegal downloads of music is an international dilemma since music is a global commodity. Sweden has been accused of being file sharers’ haven by organisations such as the Recording Industry Association of America (RIAA). Internet access and broadband capacity is very high in Sweden, which is a reason why many Swedes engage in file sharing. The Swedish company, The Pirate Bay, is the creator of one of the most popular file sharing websites in the world, using the BitTorrent application. The website offers free downloading of inter alia music, films and software. Like most peer-to-peer networks the Pirate Bay website includes copyrighted material, which often is published without the consent of copyright holders. As a result The Pirate Bay is facing a lawsuit on behalf of numerous organisations and companies in the music and film industry. The Pirate Bay is accused of contributory infringement and of preparation to commit a copyright infringement according to the Swedish Copyright Act (SwCA).  Contrary to the American copyright legislation, the SwCA does not contain any explicit provisions regarding contributory infringement. The SwCA refers to the Swedish Criminal Code, which states that preparation to copyright infringement and contributing to such infringement is illegal and punishable. There is currently a lack of Swedish case law regarding copyright infringement and there are no cases concerning contributory infringement. One reason is that the field of law is constantly changing; the copyright legislation is adjusted to the technological developments. The lack of case law causes unpredictability of the SwCA, which may be harmful to the rule of law. International organisations, such as the RIAA, consider the SwCA to be somewhat ineffective and that it needs to be amended in order to uphold the fundamental purpose of copyright. Copyright is a partly harmonised area of law from a global perspective. However, since the Internet and file sharing through peer-to-peer networks is an international phenomenon, copyright legislation needs further harmonisation internationally. At the time there is an ongoing process of implementing the European Union (EU) Enforcement Directive into the SwCA, which grants greater rights to copyright holders. The Directive contains provisions that simplify the process of taking action against an alleged infringer, which may in the long run increase the amount of case law in Sweden. At the same time the implementation of the Enforcement Directive has been criticised as being too far reaching and intruding people’s privacy. File sharing through peer-to-peer networks benefits consumers by offering easy access to a wide range of music for a low cost, at the same time enabling artists to reach out to a larger audience. Consumers are vital for the music industry, since they purchase the music. However, the fundamental aim of copyright is to reward copyright holders and function as an incentive to encourage creativity. Consequently, without economic rights the incentive to create is forfeit and music production might decrease. Even if the justification of copyright is primarily to protect creators of a work, it is also essential to emphasise the consumer aspect. Therefore it is of importance to balance the interests of all parties involved. In order to uphold the purpose of copyright and interests of the general public, it is necessary to promote and develop more legal file sharing alternatives. Music in digital formats has to some extent replaced the traditional Compact Disc (CD) format. Therefore the music industry must cooperate with among others Internet Service Providers (ISPs) in order to embrace the digital developments of music and offer better solutions to consumers. Simultaneously, there is a lack of knowledge of copyright among the Swedish population, which is why more education is required. In conclusion, advertisement and education could decrease illegal file sharing and enhance all the parties’ interests. / Dagens fildelningsteknologi i peer-to-peer nätverk är genial. Peer-to-peer är nätverk bestående av flera sammankopplade datorer som möjliggör fildelning mellan användare. En betydande mängd av de delade filerna utgör dock olagliga kopior; uppladdning och nedladdning av sådana filer bryter mot upphovsrättslagstiftningen. Fildelning genom peer-to-peer nätverk är därför både genial teknologi och upphovsrättsintrång. Peer-to-peer teknologin har väckt stor debatt i media, både nationellt och internationellt. Frågan kring illegal nedladdning av musik är ett internationellt dilemma eftersom musik är en global handelsvara. Sverige har kritiserats av organisationer som Recording Industry Association of America (RIAA) för att vara en frizon för fildelare. Tillgången till internet och bredband är väldigt hög i Sverige, vilket är en anledning till varför många svenskar fildelar. Det svenska företaget The Pirate Bay som använder sig av BitTorrent protokollet, är skapare till en av världens populäraste fildelningssajter. Webbsidan erbjuder gratis nedladdning av bland annat musik, film och programvara. I likhet med de flesta peer-to-peer nätverk innehåller The Pirate Bay’s hemsida upphovsrättsskyddat material som ofta har blivit tillgängliggjort utan upphovsrättshavarens medgivande. Till följd av detta har ett flertal organisationer och företag inom musik- och filmindustrin ingett en stämningsansökan mot The Pirate Bay.         The Pirate Bay är åtalade för medhjälp och förberedelse till brott mot upphovsrättslagen. I motsats till den amerikanska lagen om upphovsrätt innehåller inte den svenska upphovsrättslagen några uttryckliga bestämmelser rörande medhjälp till brott mot upphovsrätt. Upphovsrättslagen hänvisar istället till brottsbalken som stadgar att förberedelse och medverkan till brott är olagligt och straffbart. I dagsläget finns endast ett fåtal svenska rättsfall angående upphovsrättsintrång men inga fall kring medhjälp till upphovsrättsintrång. En bidragande faktor kan vara att rättsområdet ständigt ändras; upphovsrättslagstiftningen anpassas kontinuerligt till den tekniska utvecklingen. Bristen på svenska rättsfall leder till att upphovsrättslagens tillämpning blir oförutsägbar, vilket kan vara skadligt för rättsäkerheten. Internationella organisationer som exempelvis RIAA anser att den svenska upphovsrättslagen är ineffektiv och att ändringar behöver göras för att upprätthålla upphovsrättens grundläggande syfte.       Upphovsrätten är till viss del en harmoniserad lagstiftning ur ett globalt perspektiv. Eftersom internet och fildelning genom peer-to-peer nätverk är ett internationellt fenomen behöver upphovsrättslagen ytterligare harmonisering på ett internationellt plan. I dagsläget pågår en implementering av Europeiska Unionens (EU:s) sanktionsdirektiv som tillerkänner större rättigheter till upphovsrättshavare. Direktivet innehåller bestämmelser som förenklar möjligheten för rättighetshavare att vidta åtgärder mot personer som begår upphovsrättsintrång, vilket på sikt kan komma att bidra till en ökad mängd rättsfall. Sanktionsdirektivet har samtidigt kritiserats för att vara alltför långtgående och inskränker människors rätt till privatliv. Fildelning genom peer-to-peer nätverk är förmånligt för konsumenter genom att utbudet av musik är stort, lättillgängligt och till en låg kostnad; samtidigt ger nätverken artister möjligheten att nå ut till en bredare publik. Konsumenter är nödvändiga för musikindustrin eftersom de inhandlar musiken. Dock är det viktigt att upprätthålla det fundamentala syftet med upphovsrätt, vilket är att ersätta upphovsrättshavaren för sitt verk och fungera som ett incitament till att stimulera skapade. Utan de ekonomiska rättigheterna skulle uppmuntran att skapa nya alster gå förlorad, och musikproduktionen skulle minska. Trots att upphovsrätten rättfärdigas genom att skydda rättighetshavare så är det även angeläget att understryka värdet av konsumenterna. Det är därför av stor vikt att balansera samtliga parters intressen. Det är nödvändigt att marknadsföra och utveckla fler lagliga fildelningsalternativ för att upprätthålla upphovsrättens syfte och samhällets intresse. Digital musik har till viss del ersatt det traditionella Compact Disc (CD) formatet. Musikindustrin måste därför samarbeta med bland annat internetleverantörer för att ta till sig den digitala utvecklingen av musik och erbjuda bättre lösningar till konsumenter. För närvarade har den svenska befolkningen otillräckliga kunskaper inom upphovsrätt, varför mer utbildning behövs. Avslutningsvis, skulle marknadsföring och utbildning kunna bidra till en minskning av den illegala fildelningen och gynna alla parters intressen.

This thesis defines a generic framework that allows building high level services, of both data search and content distribution, for structured peer-to-peer networks (SPN). We consider a twofold genericity: (i) Extensible framework for services and applications, with a dynamic deploy over other P2P systems; and (ii) generic and portable framework over most of the SPNs. / Esta tesis construye un marco de trabajo genérico que permite construir servicios de alto nivel, tanto de gestión de datos como de distribución de contenidos, para redes peer-to-peer estructradas (RPE). Consideramos que la genericidad proporcionada es doble: (i) Marco de trabajo extensible para servicios y aplicaciones, con un despliegue dinámico sobre diferentes sistemas peer-to-peer; (ii) Marco de trabajo genérico y portable de la mayoría de RPEs.

<p>Today’s technology of music file sharing in peer-to-peer networks is genius. Peer-to-peer are networks composed of several computers enabling files to be shared among users. A substantial part of the files shared constitute unlawful copies; uploading and downloading of such files infringes copyright legislation. File sharing through peer-to-peer networks is therefore both a genius technology and a copyright infringement.</p><p>Peer-to-peer technology has been subject to heavy debate in media, both nationally and internationally. The issue of illegal downloads of music is an international dilemma since music is a global commodity. Sweden has been accused of being file sharers’ haven by organisations such as the Recording Industry Association of America (RIAA). Internet access and broadband capacity is very high in Sweden, which is a reason why many Swedes engage in file sharing. The Swedish company, The Pirate Bay, is the creator of one of the most popular file sharing websites in the world, using the BitTorrent application. The website offers free downloading of <em>inter alia</em> music, films and software. Like most peer-to-peer networks the Pirate Bay website includes copyrighted material, which often is published without the consent of copyright holders. As a result The Pirate Bay is facing a lawsuit on behalf of numerous organisations and companies in the music and film industry.</p><p>The Pirate Bay is accused of contributory infringement and of preparation to commit a copyright infringement according to the Swedish Copyright Act (SwCA).  Contrary to the American copyright legislation, the SwCA does not contain any explicit provisions regarding contributory infringement. The SwCA refers to the Swedish Criminal Code, which states that preparation to copyright infringement and contributing to such infringement is illegal and punishable. There is currently a lack of Swedish case law regarding copyright infringement and there are no cases concerning contributory infringement. One reason is that the field of law is constantly changing; the copyright legislation is adjusted to the technological developments. The lack of case law causes unpredictability of the SwCA, which may be harmful to the rule of law. International organisations, such as the RIAA, consider the SwCA to be somewhat ineffective and that it needs to be amended in order to uphold the fundamental purpose of copyright.</p><p>Copyright is a partly harmonised area of law from a global perspective. However, since the Internet and file sharing through peer-to-peer networks is an international phenomenon, copyright legislation needs further harmonisation internationally. At the time there is an ongoing process of implementing the European Union (EU) Enforcement Directive into the SwCA, which grants greater rights to copyright holders. The Directive contains provisions that simplify the process of taking action against an alleged infringer, which may in the long run increase the amount of case law in Sweden. At the same time the implementation of the Enforcement Directive has been criticised as being too far reaching and intruding people’s privacy.</p><p>File sharing through peer-to-peer networks benefits consumers by offering easy access to a wide range of music for a low cost, at the same time enabling artists to reach out to a larger audience. Consumers are vital for the music industry, since they purchase the music. However, the fundamental aim of copyright is to reward copyright holders and function as an incentive to encourage creativity. Consequently, without economic rights the incentive to create is forfeit and music production might decrease. Even if the justification of copyright is primarily to protect creators of a work, it is also essential to emphasise the consumer aspect. Therefore it is of importance to balance the interests of all parties involved.</p><p>In order to uphold the purpose of copyright and interests of the general public, it is necessary to promote and develop more legal file sharing alternatives. Music in digital formats has to some extent replaced the traditional Compact Disc (CD) format. Therefore the music industry must cooperate with among others Internet Service Providers (ISPs) in order to embrace the digital developments of music and offer better solutions to consumers. Simultaneously, there is a lack of knowledge of copyright among the Swedish population, which is why more education is required. In conclusion, advertisement and education could decrease illegal file sharing and enhance all the parties’ interests.</p> / <p>Dagens fildelningsteknologi i peer-to-peer nätverk är genial. Peer-to-peer är nätverk bestående av flera sammankopplade datorer som möjliggör fildelning mellan användare. En betydande mängd av de delade filerna utgör dock olagliga kopior; uppladdning och nedladdning av sådana filer bryter mot upphovsrättslagstiftningen. Fildelning genom peer-to-peer nätverk är därför både genial teknologi och upphovsrättsintrång.</p><p>Peer-to-peer teknologin har väckt stor debatt i media, både nationellt och internationellt. Frågan kring illegal nedladdning av musik är ett internationellt dilemma eftersom musik är en global handelsvara. Sverige har kritiserats av organisationer som Recording Industry Association of America (RIAA) för att vara en frizon för fildelare. Tillgången till internet och bredband är väldigt hög i Sverige, vilket är en anledning till varför många svenskar fildelar. Det svenska företaget The Pirate Bay som använder sig av BitTorrent protokollet, är skapare till en av världens populäraste fildelningssajter. Webbsidan erbjuder gratis nedladdning av bland annat musik, film och programvara. I likhet med de flesta peer-to-peer nätverk innehåller The Pirate Bay’s hemsida upphovsrättsskyddat material som ofta har blivit tillgängliggjort utan upphovsrättshavarens medgivande. Till följd av detta har ett flertal organisationer och företag inom musik- och filmindustrin ingett en stämningsansökan mot The Pirate Bay.        </p><p>The Pirate Bay är åtalade för medhjälp och förberedelse till brott mot upphovsrättslagen. I motsats till den amerikanska lagen om upphovsrätt innehåller inte den svenska upphovsrättslagen några uttryckliga bestämmelser rörande medhjälp till brott mot upphovsrätt. Upphovsrättslagen hänvisar istället till brottsbalken som stadgar att förberedelse och medverkan till brott är olagligt och straffbart. I dagsläget finns endast ett fåtal svenska rättsfall angående upphovsrättsintrång men inga fall kring medhjälp till upphovsrättsintrång. En bidragande faktor kan vara att rättsområdet ständigt ändras; upphovsrättslagstiftningen anpassas kontinuerligt till den tekniska utvecklingen. Bristen på svenska rättsfall leder till att upphovsrättslagens tillämpning blir oförutsägbar, vilket kan vara skadligt för rättsäkerheten. Internationella organisationer som exempelvis RIAA anser att den svenska upphovsrättslagen är ineffektiv och att ändringar behöver göras för att upprätthålla upphovsrättens grundläggande syfte.      </p><p>Upphovsrätten är till viss del en harmoniserad lagstiftning ur ett globalt perspektiv. Eftersom internet och fildelning genom peer-to-peer nätverk är ett internationellt fenomen behöver upphovsrättslagen ytterligare harmonisering på ett internationellt plan. I dagsläget pågår en implementering av Europeiska Unionens (EU:s) sanktionsdirektiv som tillerkänner större rättigheter till upphovsrättshavare. Direktivet innehåller bestämmelser som förenklar möjligheten för rättighetshavare att vidta åtgärder mot personer som begår upphovsrättsintrång, vilket på sikt kan komma att bidra till en ökad mängd rättsfall. Sanktionsdirektivet har samtidigt kritiserats för att vara alltför långtgående och inskränker människors rätt till privatliv.</p><p>Fildelning genom peer-to-peer nätverk är förmånligt för konsumenter genom att utbudet av musik är stort, lättillgängligt och till en låg kostnad; samtidigt ger nätverken artister möjligheten att nå ut till en bredare publik. Konsumenter är nödvändiga för musikindustrin eftersom de inhandlar musiken. Dock är det viktigt att upprätthålla det fundamentala syftet med upphovsrätt, vilket är att ersätta upphovsrättshavaren för sitt verk och fungera som ett incitament till att stimulera skapade. Utan de ekonomiska rättigheterna skulle uppmuntran att skapa nya alster gå förlorad, och musikproduktionen skulle minska. Trots att upphovsrätten rättfärdigas genom att skydda rättighetshavare så är det även angeläget att understryka värdet av konsumenterna. Det är därför av stor vikt att balansera samtliga parters intressen.</p><p>Det är nödvändigt att marknadsföra och utveckla fler lagliga fildelningsalternativ för att upprätthålla upphovsrättens syfte och samhällets intresse. Digital musik har till viss del ersatt det traditionella Compact Disc (CD) formatet. Musikindustrin måste därför samarbeta med bland annat internetleverantörer för att ta till sig den digitala utvecklingen av musik och erbjuda bättre lösningar till konsumenter. För närvarade har den svenska befolkningen otillräckliga kunskaper inom upphovsrätt, varför mer utbildning behövs. Avslutningsvis, skulle marknadsföring och utbildning kunna bidra till en minskning av den illegala fildelningen och gynna alla parters intressen.       </p>

Στο πλαίσιο της διδακτορικής διατριβής αυτής προσπαθήσαμε να δώσουμε λύση στο κεντρικό πρόβλημα του σχεδιασμού και της υλοποίησης κατανεμημένων αρχιτεκτονικών συστήματος, πρωτοκόλλων και αλγορίθμων που παρέχουν την αναγκαία υποδομή για τον υπολογισμό ορισμένων βασικών καθολικών ιδιοτήτων και μεταβλητών της κατάστασης ενός Δικτύου Ομοτίμων Εταίρων (ΔΟΕ). Μπορούμε να διακρίνουμε δύο κύριες διαστάσεις καθολικών ιδιοτήτων: (α) ιδιότητες που αναφέρονται στους κόμβους του δικτύου και τα ιδιαίτερα χαρακτηριστικά τους (υπολογιστική ισχύ, συμπεριφορά, κτλ.) και (β) ιδιότητες και μεταβλητές των αντικειμένων/δεδομένων που χειρίζεται το ΔΟΕ. Για το σκοπό αυτό, κινηθήκαμε προς δύο αλληλοσυμπληρούμενες κατευθύνσεις: (α) ποσοτικοποίηση και εκμετάλλευση της ετερογένειας των κόμβων ενός ΔΟΕ, και (β) υπολογισμός εκτιμήσεων καθολικών μεταβλητών του συστήματος, με απώτερο στόχο την υποστήριξη επεξεργασίας πολύπλοκων ερωτημάτων σε συστήματα διαχείρισης δεδομένων Διαδικτυακής κλίμακας. Στο πρώτο μέρος της διατριβής αυτής, ασχοληθήκαμε με το πρόβλημα της ετερογένειας στις υπολογιστικές δυνατότητες και στις συμπεριφορές των κόμβων ενός ΔΟΕ, καθ'οδόν προς ένα πιό αποδοτικό και ανθεκτικό περιβάλλον δρομολόγησης μηνυμάτων και επεξεργασίας ερωτημάτων, σε σχέση με τα κλασσικά υπάρχοντα δομημένα δικτυακά υποστρώματα ΔΟΕ Κατανεμημένων Πινάκων Κατακερματισμού. Έτσι, πρώτα παρουσιάζουμε ένα νέο παράδειγμα αρχιτεκτονικής δόμησης των ΔΟΕ, το οποίο ονομάζουμε AESOP. Ακόμα, ασχολούμαστε με το πρόβλημα της αποδοτικής επεξεργασίας ερωτημάτων εύρους σε ΔΟΕ βασισμένα σε DHT. Η καινοτομία της προτεινόμενης προσέγγισης βρίσκεται σε αρχιτεκτονικές, αλγορίθμους και πρωτόκολλα ταυτοποίησης και κατάλληλης εκμετάλλευσης δυνατών κόμβων του δικτύων αυτών. Στο δεύτερο μέρος της διατριβής αυτής, ασχολούμστε με την κατανεμημένη εκτίμηση καθολικών μεταβλητών συστημάτων ΔΟΕ, όπως ο πληθάριθμος κατανεμημένων πολυσυνόλων, η επεξεργασία καθολικών συναθροιστικών ερωτημάτων και η διατήρηση ιστογραμμάτων επί δεδομένων κατανεμημένων σε όλους του κόμβους του ΔΟΕ, ώστε να επιτρέψουμε την μεταφορά τεχνικών βελτιστοποίησης ερωτημάτων από τα κεντρικοποιημένα περιβάλλοντα στον ευρέος κατανεμημένο χώρο των συστημάτων διαχείρισης δεδομένων Διαδικτυακής κλίμακας. / As part of this doctoral thesis we tried to solve the central problem of the design and implementation of distributed system architectures, protocols and algorithms that provide the infrastructure necessary to calculate some basic global properties and variables of a peer-to-peer network. We can distinguish two main dimensions of such properties: (a) properties pertaining to the nodes of the network and their particular characteristics (computing power, behavior, etc.) and (b) properties of objects and variables/data managed by the P2P network. For this purpose, we moved in two complementary directions: (a) quantification and exploitation of heterogeneity of nodes in P2P networks, and (b) calculation of estimates of global variables, with a view to support complex query processing in Internet-scale data management systems. First, we dealt with the problem of heterogeneity in computing capabilities and behaviour patterns of the nodes in a P2P network, en route to a more efficient and fault resilient routing and query processing infrastructure compared to classic structure DHT-based data networks. So, first we present a new architecture paradigm, called AESOP. We then use this architecture to tackle the problem of efficient range query processing in DHT-based data management systems. The innovation of the proposed approach lies in architectures, algorithms and protocols for identification and proper exploitation of the powerful nodes of these networks. Then we deal with the distributed estimation of global system variables in P2P networks, such as the cardinality of distributed multisets, distributed aggregate query processing, and the maintenance of distributed histograms over data stored across all nodes of the P2P overlay, so as to allow the porting of query processing and optimization techniques from centralized environments to the widely distributed field of Internet-scale data management systems.

Abstract Energy efficiency is a powerful measure for promoting sustainability in technological evolution and ensuring feasible battery life of end-user devices in mobile computing. Peer-to-peer technology provides decentralized and self-organizing architecture for distributing content between devices in networks that scale up almost infinitely. However, peer-to-peer networking may require lots of resources from peer nodes, which in turn may lead to increased energy consumption on mobile devices. For this reason, peer-to-peer networking has so far been considered unfeasible for mobile environment. This thesis makes several contributions towards enabling energy-aware peer-to-peer networking in mobile environments. First, an empirical study is conducted to understand the energy consumption characteristics of radio interfaces and typical composition of traffic in structured peer-to-peer networks. This is done in order to identify the most essential obstacles for utilizing peer-to-peer technology in mobile environments. Second, the e-Aware model for estimating the energy consumption of a mobile device is developed and empirically verified to achieve 3-21% error in comparison to real-life measurements. Third, the e-Mon model for the energy-aware load monitoring of peer nodes is developed and demonstrated to improve the battery life of mobile peer nodes up to 470%. Fourth, the ADHT concept of mobile agent based virtual peers is proposed for sharing the peer responsibilities between peer nodes in a subnet so that they can participate in a peer-to-peer overlay without compromising their battery life. The results give valuable insight into implementing energy-efficient peer-to-peer systems in mobile environments. The e-Aware energy consumption model accelerates the development of energy-efficient networking solutions by reducing the need for time-consuming iterations between system development and evaluations with real-life networks and devices. The e-Mon load monitoring model facilitates the participation of battery-powered devices in peer-to-peer and other distributed networks by enabling energy-aware load balancing where energy-critical mobile nodes carry less load than other nodes. The ADHT facilitates the participation of constrained-capacity wireless devices, such as machine-to-machine nodes, in a peer-to-peer network by allowing them to sleep for most of their time. / Tiivistelmä Energiatehokkuus on kustannustehokas tapa vähentää päätelaitteiden käytön aiheuttamia kasvihuonepäästöjä sekä parantaa niiden akunkestoa. Vertaisverkkoteknologia tarjoaa hajautetun, itseorganisoituvan, sekä lähes rajattomasti skaalautuvan verkkoarkkitehtuurin päätelaitteiden väliseen tallennustilan, mediasisältöjen ja tietoliikennekapasiteetin suorajakamiseen. Vertaisverkkojen suurin heikkous mobiilikäytön näkökulmasta on niiden päätelaitteille aiheuttama ylimääräinen kuormitus, mikä näkyy lisääntyneenä energiankulutuksena. Tässä väitöskirjassa on tutkittu mekanismeja vertaisverkon päätelaitteiden energiatehokkuuden parantamiseksi, tavoitteena riittävä akunkesto mobiilikäytössä. Aluksi työssä tutkittiin empiirisesti langattomien verkkojen mobiilipäätelaitteille aiheuttamaa energiankulutusta sekä rakenteellisten vertaisverkkojen vertaispäätelaitteille aiheuttamaa liikennekuormitusta. Tavoitteena oli muodostaa käsitys suurimmista haasteista mobiililaitteiden käytölle vertaisverkoissa. Seuraavaksi mobiiliverkkojen energiankulutusta koskevasta havaintoaineistosta muodostettiin energiankulutusmalli, e-Aware, jolla voitiin arvioida mobiilipäätelaitteen energiankulutusta erilaisilla verkon liikenneprofiileilla. Mallilla saavutettiin parhaimmillaan kolmen prosentin keskimääräinen virhe. Kolmannessa vaiheessa kehitettiin energiatietoinen kuormanseurantamalli, e-Mon, jota käyttäen saavutettiin jopa 470 % lisäys mobiilin vertaispäätelaitteen akunkestoon. Viimeisessä vaiheessa kehitettiin ADHT-konsepti, joka on uudentyyppinen tapa jakaa vertaispäätelaitteiden kuormaa usean saman verkkoklusterin päätelaitteen kesken käyttäen laitteesta toiseen kiertävää mobiiliagenttia. Väitöskirjan tulokset osoittavat että mobiililaitteiden energiatehokkuutta vertaisverkoissa pystytään olennaisesti parantamaan energiatietoisia kuormanjakomekanismeja käyttäen. Työssä kehitetty e-Aware nopeuttaa energiatehokkaiden hajautettujen järjestelmien kehitystyötä tarjoamalla tehokkaan työkalun järjestelmän energiankulutuksen arvioimiseen jo kehitysvaiheessa. e-Mon mahdollistaa energiatietoisen kuormanjaon vertaisverkoissa tarjoamalla tarvittavan kuormanseurantamallin. ADHT puolestaan tarjoaa uudenlaisen tavan vähentää vertaisverkkojen aiheuttamaa päätelaitekuormitusta hyödyntäen maksimaalisesti rajoitetun kapasiteetin laitteiden unitilojen käyttöön perustuvaa energiankulutusoptimointia.

Le principe de l'Internet des objets (IdO) est d'interconnecter non seulement les capteurs, les appareils mobiles et les ordinateurs, mais aussi les particuliers, les maisons, les bâtiments intelligents et les villes, ainsi que les réseaux électriques, les automobiles et les avions, pour n'en citer que quelques-uns. Toutefois, la réalisation de la connectivité étendue de l'IdO tout en assurant la sécurité et la confidentialité des utilisateurs reste un défi. Les systèmes IdO présentent de nombreuses caractéristiques non conventionnelles, telles que l'évolutivité, l'hétérogénéité, la mobilité et les ressources limitées, qui rendent les solutions de sécurité Internet existantes inadaptées aux systèmes basés sur IdO. En outre, l'IdO préconise des réseaux peer-to-peer où les utilisateurs, en tant que propriétaires, ont l'intention d'établir des politiques de sécurité pour contrôler leurs dispositifs ou services au lieu de s'en remettre à des tiers centralisés. En nous concentrant sur les défis scientifiques liés aux caractéristiques non conventionnelles de l'IdO et à la sécurité centrée sur l'utilisateur, nous proposons une infrastructure sécurisée de l'IdO activée par la technologie de la chaîne de blocs et pilotée par des réseaux peer-to-peer sans confiance. Notre infrastructure sécurisée IoT permet non seulement l'identification des individus et des collectifs, mais aussi l'identification fiable des objets IoT par leurs propriétaires en se référant à la chaîne de blocage des réseaux peer-to-peer sans confiance. La chaîne de blocs fournit à notre infrastructure sécurisée de l'IdO une base de données fiable, immuable et publique qui enregistre les identités individuelles et collectives, ce qui facilite la conception du protocole d'authentification simplifié de l'IdO sans dépendre des fournisseurs d'identité tiers. En outre, notre infrastructure sécurisée pour l'IdO adopte un paradigme d'IdO socialisé qui permet à toutes les entités de l'IdO (à savoir les individus, les collectifs, les choses) d'établir des relations et rend l'IdO extensible et omniprésent les réseaux où les propriétaires peuvent profiter des relations pour définir des politiques d'accès pour leurs appareils ou services. En outre, afin de protéger les opérations de notre infrastructure sécurisée de l'IdO contre les menaces de sécurité, nous introduisons également un mécanisme autonome de détection des menaces en complément de notre cadre de contrôle d'accès, qui peut surveiller en permanence le comportement anormal des opérations des dispositifs ou services. / The premise of the Internet of Things (IoT) is to interconnect not only sensors, mobile devices, and computers but also individuals, homes, smart buildings, and cities, as well as electrical grids, automobiles, and airplanes, to mention a few. However, realizing the extensive connectivity of IoT while ensuring user security and privacy still remains a challenge. There are many unconventional characteristics in IoT systems such as scalability, heterogeneity, mobility, and limited resources, which render existing Internet security solutions inadequate to IoT-based systems. Besides, the IoT advocates for peer-to-peer networks where users as owners intend to set security policies to control their devices or services instead of relying on some centralized third parties. By focusing on scientific challenges related to the IoT unconventional characteristics and user-centric security, we propose an IoT secure infrastructure enabled by the blockchain technology and driven by trustless peer-to-peer networks. Our IoT secure infrastructure allows not only the identification of individuals and collectives but also the trusted identification of IoT things through their owners by referring to the blockchain in trustless peer-to-peer networks. The blockchain provides our IoT secure infrastructure with a trustless, immutable and public ledger that records individuals and collectives identities, which facilitates the design of the simplified authentication protocol for IoT without relying on third-party identity providers. Besides, our IoT secure infrastructure adopts socialized IoT paradigm which allows all IoT entities (namely, individuals, collectives, things) to establish relationships and makes the IoT extensible and ubiquitous networks where owners can take advantage of relationships to set access policies for their devices or services. Furthermore, in order to protect operations of our IoT secure infrastructure against security threats, we also introduce an autonomic threat detection mechanism as the complementary of our access control framework, which can continuously monitor anomaly behavior of device or service operations.

Τα τελευταία χρόνια οι εφαρμογές συνεχούς μετάδοσης ροών πληροφορίας στο διαδίκτυο έχουν γίνει ιδιαίτερα δημοφιλείς. Με τον συνεχώς αυξανόμενο ρυθμό εισόδου νέων αντικειμένων πληροφορίας, γίνεται ολοένα και πιο επιτακτική η ανάγκη για την ανάπτυξη πληροφορικών συστημάτων που να μπορούν να προσφέρουν στους χρήστες τους μόνο εκείνες τις πληροφορίες που τους ενδιαφέρουν, φιλτράροντας τεράστιους όγκους από άσχετες για τον κάθε χρήστη, πληροφορίες. Ένα μοντέλο διάδοσης πληροφορίας ικανό να ενσωματώσει τέτοιου είδους ιδιότητες, είναι το μοντέλο δημοσιεύσεων/συνδρομών βασισμένο στο περιεχόμενο ( content-based publish/subscribe) Βασική συνεισφορά μας στο χώρο είναι η εφαρμογή του μοντέλου δημοσιεύσεων/συνδρομών βασισμένου στο περιεχόμενο (content-based publish/subscribe) πάνω στα δίκτυα ομοτίμων ώστε να μπορέσουμε να προσφέρουμε στους χρήστες υψηλή εκφραστικότητα κατά την δήλωση των ενδιαφερόντων τους, λειτουργώντας σε ένα πλήρως κατανεμημένο και κλιμακώσιμο περιβάλλον. Ο κορμός των προτεινόμενων λύσεων σε αυτή τη διατριβή είναι: (α) η ανάπτυξη αλγορίθμων για την αποθήκευση των κλειδιών των δημοσιεύσεων σε κατάλληλους κόμβους του δικτύου με βάση τις συνθήκες στο περιεχόμενο που έχουν δηλωθεί και (β) αλγορίθμων δρομολόγησης δημοσιεύσεων στο διαδίκτυο έτσι ώστε να ((συναντούν)) αυτούς τους κόμβους οι οποίοι περιέχουν συνδρομές που ικανοποιούνται από την πληροφορία της δημοσίευσης. Οι προτεινόμενοι αλγόριθμοι υλοποιήθηκαν και εξετάσθηκαν ενδελεχώς με προσομοίωση μελετώντας την απόδοσή τους με βάση μετρικές όπως: η δίκαιη κατανομή του φόρτου στους κόμβους του δικτύου από τη διακίνηση μηνυμάτων κατά την επεξεργασία των συνδρομών/δημοσιεύσεων, ο συνολικός αριθμός μηνυμάτων που διακινούνται, ο συνολικός όγκος επιπλέον πληροφορίας που απαιτούν οι αλγόριθμοι να εισέλθει στο δίκτυο (network bandwidth), και ο χρόνος που απαιτείται για την ανεύρεση των συνδρομών που συζευγνύουν με κάθε δημοσίευση. / In the past few years the continuous data streams applications have become particularly popular. With the continuously increasing rate of entry of new information, it becomes imperative the need for developing appropriate infrastructures that will offer only the information that users are interested for, filtering out large volumes of irrelevant for each user, information. The content-based publish/subscribe model, is capable of handling large volumes of data traffic in a distributed, fully decentralized manner. Our basic contribution in this research area is the coupling of the content-based publish/subscribe model with the structured (DHT-based) peer-to-peer networks, offering high expressiveness to users on stating their interests. The proposed infrastructure operated in a distributed and scalable environment. The proposed solutions in this thesis are related to the development and testing: (a) of a number of algorithms for subscription processing in the network and (b) of a number of algorithms for processing the publication events. The proposed algorithms were developed and thoroughly tested with a detailed simulation-based experimentation. The performance metrics are: the fair distribution of load in the nodes of network from the distribution of messages while processing subscriptions and publication events, the total number of messages that are generated, the total volume of additional information that is required from the algorithms to operate, and the time that is required for matching publication events to subscriptions.