Made available in DSpace on 2016-08-17T14:53:02Z (GMT). No. of bitstreams: 1 Flavio_Marcilio_Paiva_Ramos.pdf: 2116529 bytes, checksum: ec39ed91f835e580a43ccfbf8a3c4d1a (MD5) Previous issue date: 2009-05-04 / Nowadays, peer-to-peer networks are very popular mainly, when we wish to search or share a considerable amount of information and resources among various participants. One of the main difficulties of this technology is how to avoid that those participants maintain, at the same time, a considerable number of shared resources and to guarantee that those resources are not corrupted or polluted content. Another problem commonly found in P2P networks is the lack of interoperability among existing P2P solutions especially because the inconsistencies of metadata and operation interfaces used in node communication. This work describes P2PWSRep, a reputation management protocol that identifies non-cooperative nodes or that can hinder network performance by sharing corrupted, infected or non-existent files. P2PWSRep infrastructure was based on web services in order to tackle interoperability problems and to facilitate its extensibility, making it feasible to be accessed by several other P2P applications. The P2PWSRep protocol employs a distributed reputation computation using an exponentially weighted average that takes into account the current and previous node reputation and which is tuned by an adjustment parameter in order to obtain the final reputation, thus considering the node s behavior. The P2PWSRep protocol is validated by means of simulation and our results show that it is able to point out the more trustable nodes in the network as well as to insulate those which are not reliable or cooperative. Besides, the protocol does not unnecessarily impacts on the network load P2PWS. / As redes peer-to-peer (P2P) são muito populares atualmente, principalmente quando se deseja buscar ou compartilhar uma grande quantidade de informações e recursos entre os seus participantes. Uma das grandes dificuldades desse tipo de tecnologia é evitar que esses participantes mantenham, ao mesmo tempo, um número considerável de arquivos compartilhados, e ainda garantir que esses arquivos não sejam conteúdo poluído ou corrompido. Outro problema bem comum nas redes P2P, é a falta de interoperabilidade entre as diversas redes existentes, principalmente devido às incompatibilidades dos metadados e das interfaces das operações utilizadas na comunicação entre os nós. Este trabalho descreve o P2PWSRep, um protocolo de gerenciamento de reputação para identificar nós que não desejam cooperar ou que podem prejudicar o desempenho da rede pelo compartilhamento de arquivos corrompidos, infectados ou inexistentes. A infraestrutura da rede do P2PWSRep foi baseada em serviços web para contornar problemas de interoperabilidade e facilitar sua extensibilidade, tornando-o fácil de ser utilizado por diversas aplicações de redes P2P. O protocolo P2PWSRep possui um cállculo de reputação distribuído, utilizando-se uma média ponderada exponencial, que considera o valor da reputação anterior do nó e o valor atual, obtido dos demais nós da rede, e regulado por um parâmetro de ajuste, para obter a reputação final, de forma que o histórico do comportamento do nó seja considerado. O protocolo P2PWSRep é validado por meio de simulação e os resultados obtidos mostram que o mesmo é capaz de apontar os nós ou recursos mais confiáveis da rede, ao mesmo tempo em que isola aqueles nós que não são íntegros ou pouco cooperativos, além de não impor uma sobrecarga desnecessária à rede P2PWS.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-06T18:14:11Z No. of bitstreams: 1 vitorfreitasesouza.pdf: 4838221 bytes, checksum: 593f759949de45c0b044f62ba94f9a1a (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-06-07T13:31:03Z (GMT) No. of bitstreams: 1 vitorfreitasesouza.pdf: 4838221 bytes, checksum: 593f759949de45c0b044f62ba94f9a1a (MD5) / Made available in DSpace on 2017-06-07T13:31:03Z (GMT). No. of bitstreams: 1 vitorfreitasesouza.pdf: 4838221 bytes, checksum: 593f759949de45c0b044f62ba94f9a1a (MD5) Previous issue date: 2015-02-27 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A concepção de workflows científicos é uma abordagem amplamente utilizada no contexto de e-Science e experimentação científica. Existem muitas pesquisas voltadas para o gerenciamento e execução de experimentos baseados em workflows. No entanto, experimentos complexos envolvem interações entre pesquisadores geograficamente distribuídos, demandando utilização de grandes volumes de dados, serviços e recursos computacionais distribuídos. Este cenário categoriza um ecossistema de experimentação científica. Para conduzir experimentos neste contexto, cientistas precisam de uma arquitetura flexível, extensível e escalável. Durante o processo de experimentação, informações valiosas podem ser perdidas e oportunidades de reutilização de recursos e serviços desperdiçadas, caso a arquitetura de ecossistema para e-Science não considere estes aspectos. Com o objetivo de tratar a flexibilidade, a extensibilidade e a escalabilidade de plataformas de ecossistemas, este trabalho apresenta uma arquitetura orientada a serviços apoiada por uma rede ponto a ponto, desenvolvida para tratar as etapas do ciclo de vida de um experimento científico. Este trabalho apresenta como contribuições uma arquitetura para ecossistemas de software científico, a implementação desta arquitetura, bem como a sua avaliação. / The conception of scientific workflows is a widely used approach in the context of eScience and scientific experimentation. There are many researches about the management and execution of experiments based on workflows. However, scientific experiments involve complex interactions between geographically distributed researchers, requiring the usage of large amount of data, services and distributed computing resources. This scenario categorizes a scientific experimentation ecosystem. In order to carry out experiments in this context researchers need an architecture for e-Science that supports flexibility, extensibility and scalability. During the experimentation process, valuable information can be unexploited and reusing opportunities of resources and services could be lost if the ecosystem architecture for e-Science does not consider previous mentioned requirements. In order to address the flexibility, extensibility and scalability of ecosystems platforms, this dissertation presents a service-oriented architecture supported by a peer-to-peer network. It was developed to support life-cycle stages of a scientific experiment. This work also presents, as contributions, an architecture to support experiments execution of scientific software ecosystems, the implementation of this architecture, as well as its evaluation.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-22T19:11:26Z No. of bitstreams: 1 edsonbrunonovais.pdf: 2331943 bytes, checksum: 8120e1755bb41cf7f2d45dd996308c9c (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T19:25:53Z (GMT) No. of bitstreams: 1 edsonbrunonovais.pdf: 2331943 bytes, checksum: 8120e1755bb41cf7f2d45dd996308c9c (MD5) / Made available in DSpace on 2017-08-07T19:25:53Z (GMT). No. of bitstreams: 1 edsonbrunonovais.pdf: 2331943 bytes, checksum: 8120e1755bb41cf7f2d45dd996308c9c (MD5) Previous issue date: 2012-08-10 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente estão acontecendo significativas mudanças na natureza do processo de pesquisa científica. Em particular, tem-se uma maior colaboração entre grandes grupos de pesquisadores, o que leva a um aumento no uso de técnicas de processamento de informação, e uma maior necessidade de compartilhar resultados e observações entre os participantes do processo. Utilizando tecnologias como Redes Ponto a Ponto e Web Semântica, conseguimos criar um único ponto de acesso a bases de conhecimento dispersas e aplicações científicas distribuídas, onde os cientistas possam trabalhar com informações heterogêneas e criar comunidades científicas de acordo com suas especialidades e interesses. Este trabalho apresenta a e-ScienceNet, uma arquitetura de suporte ao armazenamento, compartilhamento e execução de experimentos científicos em uma Rede Ponto a Ponto Semântica científica. Para tal, desenvolvemos um protótipo que realiza a interação entre os diferentes nós da rede nas distintas comunidades científicas semânticas. / Currently, there are taking place significant changes in the nature of scientific research. In particular, there is a greater collaboration among large groups of researchers, which leads to an increase in the use of information processing techniques, and a greater need to share results and observations among the participants in the process. Using technologies such as Peer to Peer Networks and the Semantic Web, we can create a single point of access to distributed knowledge bases and scientific applications, where scientists can work with heterogeneous information and create scientific communities according to their specialties and interests. This work presents the e-ScienceNet as an architecture that support the storage, share and execution of scientific experiments in a scientific Semantic Peer to Peer Network. To this end, we developed a prototype that performs the interaction between the different network nodes in different semantic scientific communities.

Peer to peer networks are becoming increasingly popular among Internet users as the downloading peers share the storage and upload bandwidth load of the system. This makes it possible for a large number of users to share a data file available at a server without the server upload bandwidth becoming a bottleneck. The P2P technology is being widely used not only for file sharing but also for video on demand, live streaming and IPTV. The delay deadlines are more stringent in live streaming and IPTV than those in file sharing as the traffic is real time. The performance perceived by a user depends upon whether the video stream is being downloaded at the streaming rate. Coolstreaming is the first large scale P2P IPTV system. We model the multi-channel Coolstreaming system via an open queueing network. The peer dynamics at a channel is modelled by a closed queueing network working at a faster rate. We compute the expected number of substreams in the overlay of New Coolstreaming which are not being received at the proper rate. The computation of the Markov chain with a very large state space is handled using the two time scale decomposition. Further we characterize the end to end delay encountered by a video stream originating from the server and received at a user of New Coolstreaming. Three factors contribute towards the delay. The first factor is the mean path length in terms of overlay hops of the partnership graph. The second factor is the mean number of routers between any two overlay peers in the network layer and the third factor is the queueing delay at a router in the Internet. The mean shortest path length in terms of overlay peers in the New Coolstreaming graph is shown to be O(logn)where nis the number of peers in the overlay. This is done by modelling the overlay by a random graph. The mean shortest path in terms of routers in the Internet’s router level topology is seen to be at most O(logNI)where NIis the number of routers in the Internet. We also discuss a method by which we can get the mean delay at a router in the Internet. Thus, the mean end to end delay in New Coolstreaming is shown to be upper bounded by O(lognlogNIE[W])where E[W]is the mean delay at a router in the Internet.

Abstrakt (svenska) Bakgrund: Piratkopieringen bara ökar och ökar. Program-, spel- och musikbranschen har idag stora problem. En i stort sett okunnig användare kan fixa en nyutgiven skiva innan den nått butikerna på grund av piratkopieringen. Detta problem möjliggörs genom att ingen bra lösning finns i form av fungerande kopieringsskydd samt att fildelningstjänsterna får stort spelrum. Vi går in specifikt och undersöker musikbranschen. Syfte: Fördjupa oss i begreppet piratkopiering. Vidare vill vi upplysa och informera såväl musikbranschen som användare om problemet och dess framtid. Vi hoppas att det resultat vi kommer fram till kan ge underlag för vidare forskning. Metod: Vår information har tagits från artiklar på Internet samt från litteratur vi ansett vara aktuell. Telefonintervjuer har skett med Magnus Mårtensson, IFPI (International Federation of the Phonographic Industry), programjuristen Anna Burén på Sveriges Radio, Per Sandin, General manager EMI marketing samt ett flertal Internetleverantörer. Vi har dessutom sammanställt en enkät som besvarats av en mängd personer. Resultat: Många av gårdagens skivköpare anser att priset för en CD-skiva är för dyrt idag. Man har upptäckt piratkopieringen med dess obegränsade funktioner samt insett hur lätt det är att få tag på gratis musik utan repressalier, vilket beror på den idag vaga och ej alltför avskräckande lagstiftningen. Musikbolagen förlorar pengar och höjer därmed priserna för skivorna samtidigt som de aktivt arbetar för att hitta det perfekta kopieringsskyddet eller för att komma på någon annan strålande lösning. Framtiden ser oviss ut och för tillfället har piratkopierarna och fildelningstjänsterna trumf på hand. Nyckelord: Mp3, CD, Kopieringsskydd, Fildelningstjänster, Upphovsrätt och Musikintressenter. / Abstract (English) Background: Illegal copying increases rapidly. Software-, game- and music industry are experiencing troubled times at the moment. Today, a practically ignorant person would have no problems to get hold of a newly published record before it reaches the stores because of the illegal copying. This problem is made possible due to that no good solution exists. Copy protection isn’t good enough and peer-to-peer-networks are bigger than ever. In this work we will examine specifically the music industry. Purpose: We will specialize in the term of illegal copying. Further we want to enlight and inform the music industry as well as the users of the problem and it´s future. We hope the result we will achieve can be a foundation for further research. Realization: We have gathered our information from articles on the Internet and also from updated literature. Interviews were made over the phone with Magnus Mårtensson, IFPI (International Federation of the Phonographic Industry), Anna Burén, lawyer of copyright at Swedish Radio, Per Sandin, General manager EMI marketing and also a lot of Internetsuppliers. We have also compilated an inquiry which has been replied to by many people. Conclusion: Many of the buyers from the past consider the cost of a CD far too high. Instead they have discovered the illegal copying and its unlimited functions. They have also realized how easy you can get new music without reprisals, which mostly depends on the vague and not to scary laws. Music companies are losing money and therefore they raise the prize of a single CD, simultaneously as they work to find the perfect copy protection. The future looks uncertain and for the moment, those who are copying along with peer-to-peer-networks have all the trumps. Keywords: mp3, CD, copy-protection, peer-to-peer-networks, copyright, illegal copying, music companies.

Abstract The popularity of social networking services emphasises the importance of user communities. As the next evolutionary step, social networking will evolve towards user communities that are dynamically established according to contextual aspects such as the shared location and/or activities of people. In this vision, distributed peer-to-peer (P2P) technologies provide a respectable alternative to the centralised client-server technologies for implementing the upcoming community-centric mobile services. This thesis focuses on the development of enabling techniques and methods for a community-centric mobile service environment and on the evaluation of users’ perceptions and user acceptance of novel community-centric mobile services. The research was carried out by first examining the applicability of different P2P system architectures for implementing the management of user communities. Next, an experimental prototype of a community-centric mobile service environment was implemented. The experimental prototype was used for evaluating the performance of the community-centric mobile service environment and for conducting the user studies of novel community-centric mobile services. The evaluation was conducted in a real deployment environment with test users. The main results are the following: (1) a conceptual analysis of the advantages and disadvantages of P2P group management systems that are implemented using architecturally distinct P2P system architectures; (2) a performance evaluation of a P2P community management system, in which each community is implemented as an independent structured P2P overlay network; (3) a novel community-centric mobile service environment and its core component, a mobile middleware, which enables the use of P2P technologies and context information as part of Web-based applications running on a Web browser; (4) an evaluation of users’ perceptions and user acceptance of novel community-centric mobile services that are related to making a selection of an entertainment premise based on its music style and voting for music in a user community. / Tiivistelmä Käyttäjäyhteisöiden tärkeys on korostunut sosiaalista verkottumista edistävien palveluiden suosion kautta. Seuraavaksi sosiaalinen verkottuminen tulee laajentumaan yhteisöihin, jotka perustetaan dynaamisesti muun muassa ihmisten yhteisen sijainnin ja/tai toiminnan perusteella. Tulevaisuuden yhteisöllisten mobiilipalveluiden toteutuksessa hajautetut vertaisverkkoteknologiat tarjoavat varteenotettavan vaihtoehdon keskitetyille asiakas-palvelin -teknologioille. Tämä väitöskirjatyö keskittyy kehittämään tarvittavia tekniikoita ja menetelmiä yhteisöllisen mobiilipalveluympäristön toteuttamiseen sekä arvioimaan käyttäjien kokemuksia uusista yhteisöllisistä mobiilipalveluista. Tutkimuksessa tarkasteltiin aluksi arkkitehtuurillisesti erilaisten vertaisverkkojärjestelmien sopivuutta käyttäjäyhteisöjen hallinnan toteutettamiseksi. Seuraavaksi tutkimuksessa toteutettiin kokeellinen prototyyppi yhteisöllisestä mobiilipalveluympäristöstä. Kokeellista prototyyppiä hyödynnettiin sekä yhteisöllisen mobiilipalveluympäristön suorituskyvyn että uusien yhteisöllisten mobiilipalveluiden käyttäjäkokemuksen arvioinnissa. Arviointi suoritettiin aidossa käyttöympäristössä testikäyttäjien avulla. Väitöskirjatyön keskisimmät tulokset ovat seuraavat: (1) käsitteellinen analyysi arkkitehtuurillisesti erilaisten vertaisverkkojärjestelmien vahvuuksista ja heikkouksista ryhmänhallintajärjestelmän toteuttamisessa; (2) sellaisen yhteisönhallintajärjestelmän arviointi, jossa jokainen yhteisö on toteutettu erillisen ja itsenäisen rakenteellisen vertaisverkon avulla; (3) uusi yhteisöllinen mobiilipalveluympäristö, jonka keskeisin osa mobiili välikerrosohjelmisto mahdollistaa vertaisverkkoteknologioiden ja kontekstitiedon käyttämisen selaimessa toimivissa Web-sovelluksissa; (4) sellaisten uusien yhteisöllisten mobiilipalveluiden käyttäjäkokemuksen arviointi, jotka liittyvät vapaa-ajan viettopaikan valitaan musiikin perusteella ja soitettavan musiikin äänestämiseen käyttäjäyhteisöissä.

This document provides information about Cisco NetFlow technology and its usage to protect networks from different types of attacks. Part of the document is a summary of common security risks in term of their detection on network and transport layer. There are specified characteristics of NetFlow data containing samples of security risks. On the basis of these characteristics, an application for detection these risks is designed and implemented.

The popularity of decentralized systems is increasing day by day. These decentralized systems are preferable to centralized systems for many reasons, specifically they are more reliable and more resource efficient. Decentralized systems are more effective in the area of information management in the case when the data is distributed across multiple peers and maintained in a synchronized manner. This data synchronization is the main requirement for information management systems deployed in a decentralized environment, especially when data/information is needed for monitoring purposes or some dependent data artifacts rely upon this data. In order to ensure a consistent and cohesive synchronization of dependent/derived data in a decentralized environment, a dependency management system is needed. In a dependency management system, when one chunk of data relies on another piece of data, the resulting derived data artifacts can use a decentralized systems approach but must consider several critical issues, such as how the system behaves if any peer goes down, how the dependent data can be recalculated, and how the data which was stored on a failed peer can be recovered. In case of a churn (resulting from failing peers), how does the system adapt the transmission of data artifacts with respect to their access patterns and how does the system provide consistency management? The major focus of this thesis was to addresses the churn behavior issues and to suggest and evaluate potential solutions while ensuring a load balanced network, within the scope of a dependency information management system running in a decentralized network. Additionally, in peer-to-peer (P2P) algorithms, it is a very common assumption that all peers in the network have similar resources and capacities which is not true in real world networks. The peer‟s characteristics can be quite different in actual P2P systems; as the peers may differ in available bandwidth, CPU load, available storage space, stability, etc. As a consequence, peers having low capacities are forced to handle the same computational load which the high capacity peers handle, resulting in poor overall system performance. In order to handle this situation, the concept of utility based replication is introduced in this thesis to avoid the assumption of peer equality, enabling efficient operation even in heterogeneous environments where the peers have different configurations. In addition, the proposed protocol assures a load balanced network while meeting the requirement for high data availability, thus keeping the distributed dependent data consistent and cohesive across the network. Furthermore, an implementation and evaluation in the PeerfactSim.KOM P2P simulator of an integrated dependency management framework, D4M, was done. In order to benchmark the implementation of proposed protocol, the performance and fairness tests were examined. A conclusion is that the proposed solution adds little overhead to the management of the data availability in a distributed data management systems despite using a heterogeneous P2P environment. Additionally, the results show that the various P2P clusters can be introduced in the network based on peer‟s capabilities. / Populariteten av decentraliserade system ökar varje dag. Dessa decentraliserade system är att föredra framför centraliserade system för många anledningar, speciellt de är mer säkra och mer resurseffektiv. Decentraliserade system är mer effektiva inom informationshantering i fall när data delas ut över flera Peers och underhållas på ett synkroniserat sätt. Dessa data synkronisering är huvudkravet för informationshantering som utplacerade i en decentraliserad miljö, särskilt när data / information behövs för att kontrollera eller några beroende artefakter uppgifter lita på dessa data. För att säkerställa en konsistent och härstammar synkronisering av beroende / härledd data i en decentraliserad miljö, är ett beroende ledningssystem behövs. I ett beroende ledningssystem, när en bit av data som beror på en annan bit av data, kan de resulterande erhållna uppgifterna artefakter använd decentraliserad system approach, men måste tänka på flera viktiga frågor, såsom hur systemet fungerar om någon peer går ner, hur beroende data kan omräknas, och hur de data som lagrats på en felaktig peer kan återvinnas. I fall av churn (på grund av brist Peers), hur systemet anpassar sändning av data artefakter med avseende på deras tillgång mönster och hur systemet ger konsistens förvaltning? Den viktigaste fokus för denna avhandling var att behandlas churn beteende frågor och föreslå och bedöma möjliga lösningar samtidigt som en belastning välbalanserat nätverk, inom ramen för ett beroende information management system som kör i ett decentraliserade nätverket. Dessutom, i peerto- peer (P2P) algoritmer, är det en mycket vanlig uppfattning att alla Peers i nätverket har liknande resurser och kapacitet vilket inte är sant i verkliga nätverk. Peer egenskaper kan vara ganska olika i verkliga P2P system, som de Peers kan skilja sig tillgänglig bandbredd, CPU tillgängligt lagringsutrymme, stabilitet, etc. Som en följd, är peers har låg kapacitet tvingade att hantera sammaberäkningsbelastningen som har hög kapacitet peer hanterar vilket resulterar i dåligsystemets totala prestanda. För att hantera den här situationen, är begreppet verktygetbaserad replikering införs i denna uppsats att undvika antagandet om peer jämlikhet, så att effektiv drift även i heterogena miljöer där Peers har olika konfigurationer. Dessutom säkerställer det föreslagna protokollet en belastning välbalanserat nätverk med iakttagande kraven på hög tillgänglighet och därför hålla distribuerade beroende datakonsekvent och kohesiv över nätverket. Vidare ett genomförande och utvärdering iPeerfactSim.KOM P2P simulatorn av en integrerad beroende förvaltningsram, D4M, var gjort[.] De prestandatester och tester rättvisa undersöktes för att riktmärka genomförandet avföreslagna protokollet. En slutsats är att den föreslagna lösningen tillagt lite overhead för förvaltningen av tillgången till uppgifterna inom ett distribuerade system för datahantering, trots med användning av en heterogen P2P miljö. Dessutom visar resultaten att de olikaP2P-kluster kan införas i nätverket baserat på peer-möjligheter.

We study Social Groups consisting of self-interested inter-connected nodes looking for common content. We can observe Social Groups in various socio-technological networks, such as Cellular Network assisted Device-to-Device communications, Cloud assisted Peer-to-Peer Networks, hybrid Peer-to-Peer Content Distribution Networks and Direct Connect Networks. Each node wants to acquire a universe of segments at least cost. Nodes can either access an expensive link to the content distributor for downloading data segments, or use the well-connected low cost inter-node network for exchanging segments among themselves. Activation of an inter-node link requires cooperation among the participating nodes and reduces the cost of downloading for the nodes. However, due to uploading costs, Non-Reciprocating Nodes are reluctant to upload segments, in spite of their interest in downloading segments from others. We define the Give-and-Take (GT) criterion, which prohibits non-reciprocating behaviour in Social Groups for all nodes at all instants. In the “Full Exchange” case studied, two nodes can exchange copies of their entire segment sets, if each node gains at least one new segment from the other. Incorporating the GT criterion in the Social Group, we study the problem of downloading the universe at least cost, from the perspective of a new node having no data segments. We analyze this NP-hard problem, and propose algorithms for choosing the initial segments to be downloaded from the content distributor and the sequence of nodes for exchange. We compare the performance of these algorithms with a few existing P2P downloading strategies in terms of cost and running time. In the second problem, we attempt to reduce the load on the content distributor by choosing a schedule of inter-node link activations such that the number of nodes with the universe is maximized. Link activation decisions are taken by a central entity, the facilitator, for achieving the social optimum. We present the asymptotically optimal Randomized algorithm. We also present other algorithms, such as the Greedy Links algorithm and the Polygon algorithm, which are optimal under special scenarios of interest. We compare the performances of all proposed algorithms with the optimal value of the objective. We observe that computationally intensive algorithms exhibit better performance. Further, we consider the problem of decentralized scheduling of links. The decisions of link activations are made by the participating nodes in a distributed manner. While conforming to the GT criterion for inter-node exchanges, each node's objective is to maximize its utility. Each node tries to find a pairing partner by preferentially exploring nodes for link formation. Unpaired nodes choose to download a segment using the expensive link with Segment Aggressiveness Probability (SAP). We present linear complexity decentralized algorithms for nodes to choose their best strategy. We present a decentralized randomized algorithm that works in the absence of the facilitator and performs close to optimal for large number of nodes. We define the Price of Choice to benchmark performance of Social Groups (consisting of non-aggressive nodes) with the optimal. We evaluate the performance of various algorithms and characterize the behavioural regime that will yield best results for node and Social Group as well.

Nous considérons une plate-forme pair-à-pair pour la Recherche d'Information (RI) collaborative. Chaque pair héberge une collection de documents textuels qui traitent de ses sujets d'intérêt. En l'absence d'un mécanisme d'indexation global, les pairs indexent localement leurs documents et s'associent pour fournir un service distribué de réponse à des requêtes. Notre objectif est de concevoir un protocole décentralisé qui permette aux pairs de collaborer afin de transmettre une requête depuis son émetteur jusqu'aux pairs en possession de documents pertinents. Les réseaux logiques sémantiques (Semantic Overlay Networks, SON) représentent la solution de référence de l'état de l'art. Les pairs qui possèdent des ressources sémantiques similaires sont regroupés en clusters. Les opérations de RI seront alors efficaces puisqu'une requête sera transmise aux clusters de pairs qui hébergent les ressources pertinentes. La plupart des approches actuelles consistent en une reconfiguration dynamique du réseau de pairs (peer rewiring). Pour ce faire, chaque pair exécute périodiquement un algorithme de marche aléatoire ou gloutonne sur le réseau pair-à-pair afin de renouveler les pairs de son cluster. Ainsi, un réseau à la structure initialement aléatoire évolue progressivement vers un réseau logique sémantique. Jusqu'à présent, les approches existantes n'ont pas considéré que l'évolution de la topologie du réseau puisse influer sur les performances de l'algorithme de reconfiguration dynamique du réseau. Cependant, s'il est vrai que, pour une configuration initiale aléatoire des pairs, une marche aléatoire sera efficace pour découvrir les pairs similaires, lorsque des clusters commencent à émerger une approche gloutonne devient alors mieux adaptée. Ainsi, nous proposons une stratégie qui applique un algorithme de recuit simulé (Simulated Annealing, SA) afin de faire évoluer une stratégie de marche aléatoire vers une stratégie gloutonne lors de la construction du SON. Cette thèse contient plusieurs avancées concernant l'état de l'art dans ce domaine. D'abbord, nous modélisions formellement la reconfiguration dynamique d'un réseau en un SON. Nous identifions un schéma générique pour la reconfiguration d'un réseau pair-à-pair, et après le formalisons en une procédure constituée de trois étapes. Ce framework cohérent offre à ses utilisateurs de quoi le paramétrer. Ensuite, le problème de la construction d'un SON est modélisé sous la forme d'un problème d'optimisation combinatoire pour lequel les opérations de reconfiguration du réseau correspondent à la recherche décentralisée d'une solution locale. Fondée sur ce modèle, une solution concrète à base de recuit simulé est proposée. Nous menons une étude expérimentale poussée sur la construction du SON et la RI sur SONs, et validions notre approche. / A Peer-to-Peer (P2P) platform is considered for collaborative Information Retrieval (IR). Each peer hosts a collection of text documents with subjects related to its owner's interests. Without a global indexing mechanism, peers locally index their documents, and provide the service to answer queries. A decentralized protocol is designed, enabling the peers to collaboratively forward queries from the initiator to the peers with relevant documents. Semantic Overlay Network (SONs) is one the state of the art solutions, where peers with semantically similar resources are clustered. IR is efficiently performed by forwarding queries to the relevant peer clusters in an informed way. SONs are built and maintained mainly via peer rewiring. Specifically, each peer periodically sends walkers to its neighborhood. The walkers walk along peer connections, aiming at discovering more similar peers to replace less similar neighbors of its initiator. The P2P network then gradually evolves from a random overlay network to a SON. Random and greedy walk can be applied individually or integrated in peer rewiring as a constant strategy during the progress of network evolution. However, the evolution of the network topology may affect their performance. For example, when peers are randomly connected with each other, random walk performs better than greedy walk for exploring similar peers. But as peer clusters gradually emerge in the network, a walker can explore more similar peers by following a greedy strategy. This thesis proposes an evolving walking strategy based on Simulated Annealing (SA), which evolves from a random walk to a greedy walk along the progress of network evolution. According to the simulation results, SA-based strategy outperforms current approaches, both in the efficiency to build a SON and the effectiveness of the subsequent IR. This thesis contains several advancements with respect to the state of the art in this field. First of all, we identify a generic peer rewiring pattern and formalize it as a three-step procedure. Our technique provides a consistent framework for peer rewiring, while allowing enough flexibility for the users/designers to specify its properties. Secondly, we formalize SON construction as a combinatorial optimization problem, with peer rewiring as its decentralized local search solution. Based on this model, we propose a novel SA-based approach to peer rewiring. Our approach is validated via an extensive experimental study on the effect of network wiring on (1) SON building and (2) IR in SONs.