Este trabalho apresenta a avaliação de diferentes algoritmos de roteamento utilizados na camada lógica ponto a ponto (P2P) adotada por um Metaescalonador que provê Qualidade de Serviços (QoS) na Computação em Nuvem. Experimentos mostram a superioridade de três algoritmos de roteamento P2P (BCR, Chord e Pastry) em relação à utilização de Round Robin, analisando-se o tempo de resposta e a variabilidade entre os resultados obtidos em diferentes testes. Os experimentos consideram, além dos algoritmos de roteamento, a influência do número de usuários e do tipo de serviço requisitado e como esses fatores interagem entre si. É apresentado ainda um estudo sobre a melhor métrica a ser adotada para representar as informações da rede. As métricas consideradas foram latência e número de saltos. Os resultados obtidos permitem determinar, com base nos objetivos especificados, qual o impacto dos sistemas P2P utilizados pelo metaescalonador na busca e descoberta de serviços em relação à forma como a qualidade de serviços é abordada / This work presents an evaluation of different routing algorithms that are employed in a logical layer peer-to-peer (P2P) that are adopted by a Metascheduler that provides quality of services (QoS) in Cloud Computing. The experiments show the superiority of three P2P routing algorithms (BCR, Chord, Pastry) in relation to Round Robin utilization, analysing the response times and the variation between the results obtained results in different tests. The experiments consider, besides the routing algorithms, the influence of the number of the users and the type of requested services and how these factors interact between themselves. Besides of this, it is presented a study about the better metric to be adopted to represent the network information. The considered metrics were the latency and number of hops. The obtained results allow to determine, based on specific objectives, the impact of the utilization of P2P systems by the metascheduler in the search and discovery of services in relation to the way that the QoS is performed

Ces deux dernières décennies les systèmes P2P de partage de fichiers sont devenus très populaires grâce aux accès à des ressources diverses, distribuées sur Internet. Parallèlement à l'évolution de cette catégorie de systèmes, les dispositifs mobiles (téléphones cellulaires, PDA et autres appareils portatifs) ont eu un grand succès sur le marché. Équipés d'une technologie de communication sans fil (Bluetooth, et Wifi), ils peuvent communiquer sans nécessiter une infrastructure particulière en utilisant un réseau mobile adhoc (Mobile Adhoc NETwork -MANET). De la même manière, les systèmes P2P peuvent être aussi déployés sur ce type de réseau et deviennent des systèmes P2P mobiles (Mobile 2P systems). Dans le cadre de cette thèse, nous nous intéressons essentiellement à la recherche d'information dans les systèmes P2P et plus précisément au problème de routage de requêtes. La première partie de la thèse, s'est focalisée sur le routage de requêtes dans les systèmes P2P sur Internet. Nous avons proposé (i) un modèle de routage sémantique basé sur l'historique des requêtes. Ce modèle est ensuite instancié pour définir une nouvelle méthode de routage par apprentissage. Pour pallier le problème de démarrage à froid, (ii) nous avons proposé une méthode prédictive de l'intention de l'utilisateur qui construit une base de connaissances à priori pour chaque pair. Enfin, (iii) nous avons proposé une méthode de routage hybride pour traiter le problème d'échec de sélection. Cette méthode est basée sur l'historique des requêtes et le regroupement de pairs dans des groupes sémantiques. La deuxième partie de la thèse, s'est focalisée sur le routage de requêtes dans les systèmes P2P mobiles. L'apparition des MANETs, a soulevé de nouveaux challenges de routage. Ces réseaux souffrent de plusieurs contraintes liées aux supports de transmission ou bien aux dispositifs mobiles. Dans ce cadre, nous avons proposé une méthode de routage pour les systèmes P2P non structurés mobiles basée sur le contexte de l'utilisateur. D'un point de vue technique, toutes ces propositions ont été développées, validées et évaluées grâce aux simulateurs PeerSim et NS2 / Peer-to-peer systems have emerged as platforms for users to search and share information over the Internet. In fact, thanks to these systems, user can share various resources, send queries to search and locate resources shared by other users. Nowadays, mobile and wireless technology has achieved great progress. These devices are also equipped with low radio range technology, like Bluetooth and Wi-Fi, etc. By means of the low radio range technology, they can communicate with each other without using communication infrastructure (e.g. Internet network) and form a mobile ad hoc network (MANET). Hence, P2P file sharing systems can be also deployed over MANET. A challenging problem in unstructured P2P systems is query routing. Researches' efficiency and effectiveness can be improved by making smart decisions for query routing. Our contributions, in this thesis, focus on two complementary axes. Firstly, our research work focalized on P2P systems over Internet. We introduced a novel semantic model for query routing based on past queries, thereafter we instantiated this model to define our specific routing method. In addition, we addressed two difficult challenging problems: (i) the bootstraping (ii) the unsuccessful relevant peers search. Secondly, we are focalized on P2P systems over MANET. Due the nature of MANET, mobile P2P systems suffer from several constraints of wireless medium and energy-limited. Indeed, query routing methods proposed for P2P system over Internet cannot be applied. In this context, we proposed a context-aware integrated routing method for P2P file sharing systems over MANET. The different contributions are developed, validated and evaluated with the network simulators PeerSim and NS2

Si le concept de décentralisation est en quelque sorte inscrit dans le principe même de l'Internet, son urbanisme actuel n'intègre ce principe que de manière limitée. La recherche d'alternatives au mode dominant d'organisation des services basés sur Internet – une concentration autour de grands ensembles de serveurs sous le contrôle des “géants” du secteur – se poursuit, en quête d'efficacité et de durabilité. En cherchant les meilleures solutions, certains développeurs se retournent vers les qualités persistantes d'une ancienne technologie, le pair-à-pair (P2P), qui replonge dans la topologie de l'Internet pré-commercial, mettant à profit les ressources des « nains » du réseau – ses marges ou sa périphérie.Cette thèse explore l'approche distribuée et décentralisée de l'architecture technique des services Internet. Il s'agit de comprendre ce que dessine une architecture de réseau décentralisée du point de vue de l'articulation des acteurs et des contenus, de la répartition de responsabilités, de l'organisation du marché et de la capacité à exercer du contrôle, des formes d'existence et des rôles d'entités telles que les nœuds du réseau, ses usagers, ses unités centrales. Ce travail analyse sous quelles conditions un réseau qui répartit à ses marges la responsabilité de son propre fonctionnement, et qui suit un modèle non hiérarchisé ou hybride, peut se développer dans l'Internet d'aujourd'hui. La thèse suit les développeurs de trois services Internet – un moteur de recherche, un service de stockage et une application pour le streaming vidéo – construits sur un modèle de réseau décentralisé, les collectifs d'usagers pionniers qui se développent avec ces services, et ponctuellement, les arènes politiques où l'on discute de l'organisation et de la gouvernance de l'Internet à moyen et long terme. / Even if the concept of decentralization is embedded to some extent at the very core of the Internet, today's “network of networks” integrates this principle only partially. The dominant organizational model for Internet-based services involves large clusters of servers controlled by the "giants" of the IT sector. The search for alternatives is in progress, aiming at different ways to achieve effectiveness and sustainability. In this quest, a number of developers look back to the evergreen qualities of a relatively old technology, peer-to-peer (P2P), that leverages the socio-technical resources of the network's "dwarfs" - its periphery or "edge" - in a way that is, in fact, closer to the pre-commercial Internet.This dissertation explores the distributed and decentralized approach to the technical architecture of Internet-based services. It illustrates the co-shaping of a decentralized network architecture and of several different dynamics: the articulation between actors and contents, the allocation of responsibilities and the capacity to exert control, the organization of the market, the forms of existence and role of entities such as the nodes of a network, its users, its central or coordinating units. This work analyses the conditions under which a network that structures itself according to a non-hierarchical or hybrid model, and delegates the responsibility of its functioning to its edge, can develop and thrive in today's Internet. The dissertation follows the developers of three Internet services - a search engine, a storage service and a video streaming application - built on primarily decentralized network models; it also follows the collectives of pioneer users developing with these services, and selectively, the political venues where the Internet's medium- and long-term organization and governance are discussed.

Companies that sell digital products such as software and movies transfer large amounts of data to its customers. In order to send this amount of data using FTP or HTTP and still maintain a high speed transfer rate it is required that the company have a large number of servers and a huge bandwidth. Servers and bandwidth costs money which means they have great costs on the distribution of their products. In order to reduce distribution costs, P2P technology can be used and the most powerful technology to transmit popular files is called BitTorrent.BitTorrent requires users to share their bandwidth. Nowadays, BitTorrent is frequently used to transfer products that are free of charge; one example is the Linux distribution Ubuntu. In these BitTorrent systems different incentives exist to motivate the users to share their bandwidth. If a company uses BitTorrent to save money and put the distribution cost on their customers, does the customers motivation to share their bandwidth disappear?To give the reader a clear picture of the subject, literature on how BitTorrent works and its different concepts have been acquired and processed. In addition to literature, a survey has been carried out in which BitTorrent users were asked about their willingness to share their bandwidth and what motivates them most in a possible commercial BitTorrent system.The result of this study shows that a marked increase in the propensity to share bandwidth appears as additional incentives are implemented to a BitTorrent system. These incentives may be of financial or functional value. Economic incentives proved to be the most requested implementation. / Företag som säljer digitala produkter så som mjukvara och film skickar stora mängder data till dess kunder. För att kunna överföra dessa mängder med FTP eller HTTP i hög hastighet till kunderna krävs det att företaget har ett stort antal servrar och enorm bandbredd. Servrar och bandbredd kostar pengar vilket betyder att företagen har stora kostnader på distribution av deras produkter. För att minska distributionskostnader kan P2P-teknik användas och den kraftfullaste tekniken för att överföra populära filer heter BitTorrent.BitTorrent kräver att användare delar med sig av sin bandbredd. I dag används BitTorrent ofta för att överföra produkter som är gratis, ett exempel är Linuxdistributionen Ubuntu. I dessa BitTorrent-system motiveras användarna att bidra med sin bandbredd för att ge tillbaka någonting till gemenskapen. För att spara pengar kan företaget sprida ut kostnader för distribution till kunderna. Vad händer med kundens motivation att dela med sig av sin bandbredd i detta fall?Litteratur om hur BitTorrent fungerar och dess olika begrepp har samlats in och bearbetats. Utöver tidigare litteratur har en enkätundersökning genomförts där BitTorrent-användare tillfrågats om deras relation till att bidra med bandbredd och vad som motiverar dem mest i ett eventuellt kommersiellt BitTorrent-system.Resultatet av undersökningen visar att en tydlig ökning av benägenhet att dela med sig av bandbredd infinner sig då ytterligare incitament tillförs i BitTorrent-system. Dessa incitament kan vara ekonomiska eller funktionella värden. Ekonomiska incitament visade sig dock vara de mest efterfrågade.

As the global wireless network becoming mature, the growing number of mobile devices, and the personal need of keeping in touch with others daily, mobile communication is becoming a necessity of life. Using mobile devices, such as cell phones or PDAs, everyone could communicate with each other independently; and this communication environment is similar with P2P network. Utilizing the connection network of cell phones is becoming a brand new business channel. Since group-buying is part of our daily life, people live in the same area could buy products or services together based on mutual needs, and this could enhance the bargaining power of customers and lower the purchase price. This research proposes a group-buying system architecture under mobile environment, and discusses the problems that customers might encounter in every stage of the buying process. Mobile device users under the environment could exchange information with each other and this could help customers search group-buying information efficiently. Sensor Network combines with MP2P Network accelerates the spread of group-buying information in a marketplace, and helps the originator and other buyers to negotiate with the supplier. Based on the observation of the variation of the group-buying information distribution in the experiment, we summarize under what situation a better information distribution would take place in a specific marketplace.

The goodness of group buying is consumers can buy product with lower price, and seller can reduce the bargain cost by collecting orders. But it is hard to be realized in the mall. A recent survey shows most everyone has his own mobile device. In this research, we organize a mobile P2P network by exchanging between two mobile devices. We propose a system for consumers and sellers to exchange group buying information. In Mobile P2P Network environment, group buying initiator is hard to decide the best timing to end the group buying. Because buyers can easily participate or leave the group buying group, and initiator may not know the exactly how many buyers participate the group buying. So we simulate a virtual mall with the realistic data and try to find the suitable group buying model in this environment. Then we examine if participation externality effect, price drop effect and ending effect will appear in this model. Finally, we observe the trend of the number of buyers in group buying to suggest the group buying ending time. The research result indicates that participation externality effect and price drop effect still appear in the Mobile P2P Network environment. But ending effect is not obvious. Because the group buying information is distributed by participating buyers, the distribution will affect the trend of participation and participation externality effect. With suggestion of the system, initiator will not waste much time to wait few participations, and participators can reduce the time cost.

P2P借貸及股權模式群眾募資(即所謂金融回報型群眾募資)在過去五年間快速地成長，被認為係使中小企業及新創公司可有效率籌資之工具。為維持其制度之功能-籌資之效率性，在對籌資公司或平台之規範強督不宜過高，以降低其法規遵循成本。惟由於投資P2P借貸及股權模式群眾募資伴隨許多種類之風險，故在降低對籌資公司或平台之法規遵循負擔時，投資人保護之問題亦不可忽視，如何在此二者間達成平衡，為監管上之重要議題。 本文首先介紹在P2P借貸或股權模式已有發展或正在發展之美國、英國以及日本之規範概況。其次，在我國法部分，先就我國之股權模式群眾募資規範之發展為介紹，並參照比較法之規範為評析。其後，則就我國若引進P2P借貸制度，在我國既有法制如銀行法上可能碰到之問題及規範方向為分析。 在股權模式部分，櫃買中心在2014年1月開始營運功能相似之創櫃板。於2015年，金管會宣布證券經紀商經主管機關核准後，可經營股權性質群眾募資平台(後稱民營平台)，二者均受櫃買中心所發布之法規命令所規範。創櫃板與民營平台在功能及規範上有其相似之處，當二者在未來採雙軌並行時，可能有市場區隔及風險控制不足與櫃買中心在主導創櫃板同時，亦作為民營平台之監管者之利益衝突等問題。再者，在各自制度之問題上，二者亦有共通之處。關於投資人保護部分，第一，投資人可否適用相關規範為救濟，除證交法之反詐欺條款外，目前尚不明確。其次，關於投資限額之規範，則有計算與驗證限額之方式與轉售限制之規範必要性及周邊問題等之討論。關於籌資公司，則有籌資限額規範之寬嚴問題及僅可發行普通股之規範等之討論。在平台業者之規範，在民營平台部分，有關於平台業者准入規範、名義股東制度之可行性、單一業務經營及重大禁止行為等問題之討論。 在P2P借貸制度部分，關於我國法制，本文認為在各該模式是否使平台甚而借用人有構成銀行法收受存款之問題未能被釐清之前，P2P借貸制度恐無法被順利引進，可能須透過銀行法之修正，並輔以主管機關之解釋始能解決此一問題。關於對P2P借貸平台之規範，P2P借貸平台是否被定位為金融機構之一環，亦可能影響其應遵循之法律或規範為何。惟本文認為為促進P2P借貸平台之發展，即使主管機關將其定位為金融機構之一環，亦需適當設置例外，藉此可避免繁重之法規遵循成本讓使P2P借貸之制度失其設計之原意。關於貸與人之保護，在救濟途徑、投資限額、風險之評估與預告、中間帳戶之監管、資訊揭露、平台是否應提存準備金及設置意外準備基金、貸與人是否適用存款保險制度以及平台倒閉時對流通在外借款之處理機制等，亦應設置相關規範，惟亦應注意貸與人保護與上述平台法規遵循成本之平衡問題。在法規之規範方式上，本文則認為P2P借貸之商業模式可能乃與傳統借貸之商業模式有所落差，而平台之定位亦可能與傳統金融機構有所不同，故認為宜單獨就P2P借貸修訂專法或至少由主管機關單獨訂定法規命令，較為妥適。 / P2P lending and equity crowdfunding (so called “financial return crowdfunding,” FR crowdfunding for short), having grown rapidly in the last 5 years, are considered as an efficient vehicle for funding small and medium enterprises as well as start-ups. For maintaining the function of FR crowdfunding that is the efficiency of raising fund, it’s not appropriate to put strong regulations on the enterprises needing fund and the platforms of FR crowdfunding. However, because investing in FR crowdfunding associates with several types of risks, while reducing the burdens of the enterprises or platforms on compliance with the regulations, the issue of investor protection also cannot be ignored. How to balance between these two topics mentioned above is an important issue on the regulations of FR crowdfunding. Firstly, this article introduces the regulations on FR crowdfunding in U.S., Britain and Japan where P2P lending or equity crowdfunding has developed or is developing. Secondly, in the regulation of Taiwan, the article presents the regulation on equity crowdfunding of Taiwan first and make some comments, referred to the foreign regulations mentioned above. Afterwards, the article analyzes the problems, encountered on the existing laws, such as the Banking Law, and studies how to regulate P2P lending, if P2P lending is introduced to Taiwan. In the section of the equity crowdfunding, Taipei Exchange (GreTai Securities Market) started Incubation Board for Startup and Acceleration Firms (GISA) in January 2014 whose function is similar to that of the equity crowdfunding platforms. In 2015, Financial Supervisory Commission declared that securities brokers are permitted to operate platforms of equity crowdfunding (called private platforms hereinafter) once the securities brokers are authorized by the competent authority. Both GISA and private platforms are regulated by the regulations issued by Taipei Exchange. The functions and the regulation structures of GISA and private platforms are similar. When GISA and private platforms operate in a double-track way in the future, there are some problems like the insufficiency of market segmentation and risk control. Because upon the regulations, Taipei Exchange also supervises the private platforms, there exists a problem of interest conflict. Moreover, the regulations of GISA and private platforms also have common issues. About the protection of investor, firstly, whether the remedy regulations of other laws could apply for the investors of GISA and private platforms, except for the anti-fraud regulation of Securities and Exchange Act, is not clear so far. Secondly, there are also some discussions on the regulation of investment cap like the approach to calculate and verify the cap, the necessity of the measure of resale limitation, etc. About the enterprises raising fund on the GISA or private platforms, there are some discussions on whether the cap of raising fund should be higher and whether those enterprises should be permitted to offer preferred stock to raise fund, etc. About the platform, concerning to the regulations on the private platforms, there are some discussions on the industry access regulation, the feasibility of nominee structure, the operation of single business and the acts prohibited by the regulation, etc. In the section of the P2P lending, the article notes that before the problem, whether the borrowers or the platforms under different business models be considered as doing the business of accepting deposits under the Banking Law, could be clarified, it’s afraid that P2P lending cannot be introduced to Taiwan smoothly. This problem could be solved by the amendment of the current Banking Law or by the legal interpretations issued by the competent authority of Banking Law. About the regulations to the P2P lending platforms, whether the P2P lending platforms are considered as a financial institution affects which laws or regulations the P2P lending platforms might obey. However, for promoting the development of P2P lending, the article thought even if P2P lending platforms are considered as a financial institution, it’s necessary to set exceptions appropriately on it. By doing that, the purpose of P2P lending might not be destroyed by the heavy burden of compliance of regulations. About the protection of lenders, the regulations on P2P lending should include the issues on remedies of P2P lenders, investor investment cap, rating and precaution of risk, the supervision on the account of fund raised from lenders, information disclosure, whether the platforms should deposit reserves and set contingency fund, whether P2P lenders are protected by the deposit insurance, and the mechanism to deal with the loans still outstanding in case of the platform failure. However, the issue of balancing the lenders protection and the cost of regulatory compliance of the platforms still need to be considered. About how to regulate P2P lending, the article thinks that the business model of P2P lending is different from traditional lending model and that the P2P platforms are also different from the traditional financial institutions. Consequently, the article thinks that it’s appropriate to make laws or regulations singly for P2P lending.

DHT sistemų privalumas yra jų didelis plečiamumas ir nepriklausomumas, tačiau esami paieškos sprendimai reikalauja išorinių mechanizmų ir taip mažina DHT privalumus. Šio darbo tikslas – padidinti paieškos DHT sistemose galimybes, sukuriant vidinį paieškos mechanizmą Chord algoritmo pagrindu veikiančiai DHT sistemai ir ištiriant jo efektyvumą. Šiame darbe pristatomi galimi vidinės paieškos mechanizmai DHT sistemose pagrįsti n-gramomis ir užtvindymo pranešimais mechanizmu. Tyrimas parodė, kad n-gramos labiau tinkamos sistemoms, kurių dydis yra santykinai mažas, tuo tarpu užtvindymo mechanizmas priimtinesnis sistemose, kuriose įgyvendintas duomenų replikavimas. / The key idea of DHT systems is hash table distributed over the distributed independent nodes. The DHT are decentralized, scalable, fault tolerant and have high hit guaranties for data lookup. However, they do not support arbitrary querying which flooding schemes do: users must know exact key of the resource they are looking up in the system. In the most common solution for this is external searching engine like ftp or http. This work presents research experiment of possible methods for arbitrary querying in DHT based on the “n-grams” and “broadcasting” techniques. Experiment was carried out using experimental P2P system created for this purpose on the base of Chord algorithm. Experimental results showed that, the most expensive (in terms of message generation) process in “n-gram” is publishing of keys to network. The analysis of both methods showed that n-grams are more practical on the relatively smaller network and “broadcasting” is more effective on the networks with implemented data replication.

Paskirstytos maišos lentelės modeliai ir jų saugumo problemos yra aktyviai nagrinėjama sritis akademinėje bendruomenėje. Šiame darbe keliama hipotezė, kad praktinės DHT tinklų realizacijos neužtikrina teoriniuose modeliuose priimtos sąlygos, kad mazgų prisijungiančių prie tinklo identifikatoriai bus generuojami atsitiktinai. Randamas atakų sudėtingumo įvertis, kai atsitiktinių identifikatorių generavimas yra privalomas ir kai identifikatorius galima pasirinkti laisvai. Hipotezės patvirtinimui atliekamas eksperimentas. Surenkami ir analizuojami vieno didžiausių DHT tinklų (BitTorrent DHT) duomenys. Aprašomas literatūroje siūlomas problemos sprendimo būdas ir praktinės problemos kylančios jį realizuojant. Pasiūlomas naujas praktiškai pritaikomas ir našus identifikatorių generavimo patikrinimo metodas bei metodas naujų identifikatorių generavimo greičiui DHT tinkle valdyti. / Distributed Hash Table models and its security implications, has long been a subject of interest. This thesis is based on the assumption that practical implementations do not enforce random node id generation regardless of the fact that theoretical models require node ids to be chosen by random and distributed in the address space uniformly. To measure the impact on the DHT network security if the assumption holds an analysis of attack complexity in both cases is performed. Results indicate that the complexity grows from O(1) to O(M) if the node id cannot be selected arbitrarily (M is the number of nodes in DHT network). Stated assumption is confirmed by analysing classic node id protection methods and performing analysis of BitTorrent DHT network. The reason for the lack of node id protection in practice is considered to be the complexity and performance penalty of the classic methods. To facilitate the implementations of DHT networks a new method to ensure random node id generation and copy protection is provided. Proposed method utilizes MACs based on shared keys to provide a proof of the ownership of the node id while still providing means to protect it from being copied. Efficiency of the proposed method is evaluated by conducting an experiment. In order to protect small DHT networks against a Sybil attack a method to control the speed of node id generation is also proposed.

Τα τελευταία χρόνια είδαν την άνθιση διαδικτυακών εφαρμογών και υπηρεσιών διαμοιρασμού αντικειμένων πολυμέσων. Την τιμητική τους είχαν τα αντικείμενα οπτικοακουστικού περιεχομένου (video), δίνοντας πρωταγωνιστικό ρόλο στην ανάπτυξη συστημάτων διαμοιρασμού βίντεο. Μάλιστα, ανταποκρινόμενα στην δυνατότητα των χρηστών για επιλογή περιεχομένου, που παρείχαν η ραγδαία αύξηση της χρήσης του διαδικτύου και η βελτίωση των υποδομών αυτού, έγιναν ιδιαίτερα δημοφιλή τα συστήματα και οι υπηρεσίες διαμοιρασμού βίντεο κατόπιν ζήτησης Ωστόσο οι αυξημένες απαιτήσεις τους σε κλιμάκωση, προσαρμοστικότητα, απόδοση και ανεκτικότητα σε σφάλματα, κατέστησαν απαραίτητη την υποστήριξή τους από κατανεμημένες ή και παράλληλες αρχιτεκτονικές. Μία αρκετά υποσχόμενη προσέγγιση προς αυτή την κατεύθυνση είναι τα διομότιμα συστήματα καθώς οι ίδιοι οι χρήστες των εφαρμογών διαθέτουν ένα τεράστιο σύνολο από δικτυακούς και υπολογιστικούς πόρους. Στα συστήματα αυτά το περιεχόμενο που κατεβάζουν οι χρήστες διασπάται σε κομμάτια τα οποία ανταλλάσσονται από αυτούς ,με σκοπό την τελική επανασύνδεση και ανάκτηση του συνολικού μεγέθους των δεδομένων. Σκοπός αυτής της διπλωματικής είναι η μελέτη της αξιοποίησης του εύρους ζώνης στα πλαίσια ενός διομότιμου συστήματος διαμοιρασμού βίντεο κατόπιν ζήτησης με πολλαπλά κανάλια. Η παρατήρηση του τρόπου συμπεριφοράς των χρηστών και του συνολικού συστήματος ως προς τον πολύτιμο αυτό δικτυακό πόρο, μπορεί να αποτελέσει την βάση για την ανάπτυξη εφαρμογών με μεγαλύτερη αποδοτικότητα, πιο οικονομικών στην λειτουργία τους, και με βελτιωμένη ευελιξία. / The last year saw the flourishing of Internet applications and services sharing media objects. Their honor were the objects of audiovisual content (video), giving a leading role in the development of video sharing. Indeed, in response to users' ability to select content, provided by the rapid growth of internet usage and to improve the infrastructure of this, became very popular in the systems and services for sharing video on demand However, the increased demands on scalability, flexibility, performance and fault tolerance, made it necessary to support them or from distributed and parallel architectures. A very promising approach in this direction is the diomotima systems and the users themselves applications have a huge amount of network and computing resources. In these systems the content download users cleaved into pieces which are exchanged by them, with the final reconnection and recovery of the total size of data. The aim of this thesis is to study the utilization of bandwidth within a peer sharing system video on demand with multiple channels. The observation of how user behavior and the overall system to this valuable web resource, can provide the basis for developing applications with greater efficiency, more economical to operate, and with improved flexibility.