As the Internet develops and technology evolves, multimedia traffic dominates the Internet. Traditional client-server based video streaming solutions are expensive and suffering from the scalability issue. Inspired by the immense success and efficiency of BitTorrent in distributing file contents to large groups of users, the peer-to-peer (P2P) paradigm has been adopted to provide streaming services including both P2P video-on-demand (VoD) and P2P live streaming. Among the design challenges, one open yet fundamental question is, how to identify the most suitable neighbor for a peer to make a piece request. We refer this problem as the request peer selection problem. Properly allocating the piece request to potential providers is essential to the system and would help to balance the load at each peer. A well designed request peer selection algorithm increases the requestor’s probability to download the desired piece timely which leads to enhanced video quality and improved playback continuity. This thesis aims to enhance the overall system performance by proposing optimized request peer selection algorithms for both P2P VoD and P2P live streaming systems. In P2P VoD, participating peers start playback from the very beginning of a stored video. The playback-points of peers, as well as the amount of video contents/pieces the peers cached, depend on when they join the video session, or their viewing ages. The content buffered by younger peers is a subset of older peers, thus collaborative piece exchange among peers is undermined due to the unbalanced supply and demand. To address this issue, a playback-point based request peer selection algorithm: closest playback-point first (CPF) is proposed. Specifically, when a peer requests a particular video piece, among the set of potential providers, a request is sent to the peer that has the smallest playback-point difference with itself. With CPF, peers with similar content availability are loosely grouped into clusters to maximize the utilization of individual peer’s upload capacity. Extensive packet level simulations show that with CPF, the video playback quality is enhanced and the VoD server load is significantly reduced. Unlike P2P VoD, P2P live streaming systems have to meet real-time playback constraints, which makes it even more challenging. To better regulate the network traffic and to balance the load among peers, a service response time (SRT) based request peer selection algorithm is proposed. In particular, a peer in the network estimates the service response time (SRT) between itself and each neighboring peer. SRT is measured from when a data piece request is sent until the requested piece arrives. When a peer makes a piece request, the neighbor with smaller SRT and fewer data pieces would be favored. The rationale is: smaller SRT implies excess serving capacity and fewer data pieces suggests fewer potential piece requests received. Extensive packet level simulations show that the traffic load in the network is better balanced, the streaming server load is reduced, and the overall quality of service, measured by playback continuity, startup delay etc., is improved. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Peer-to-peer (P2P) paradigm, for its scalability and low cost management, is widely used in today’s network. Based on the typical designs for request/response services, a lot of efforts have been made to support publish-subscribe services in P2P networks. Gossip-based publish-subscribe system, which is commonly used in unstructured P2P networks, can provide great flexibility in query language and does not require special efforts on maintaining topology. The purpose of our work is to investigate effective and efficient mechanisms to build gossip-based publish-subscribe systems in unstructured P2P networks. Specifically, the probabilistic bi-quorum system (PBQS), for its assurance in effectiveness, becomes the object of our study. Uniform sampling is a fundamental tool to construct PBQS. By adopting uniform sampling, PBQS provides a bound on the likelihood that data messages will find a copy of the subscription. A random walk of length O(log n) is commonly used to gain a uniform sample on an expander graph of size n. To obtain a multitude of uniform samples thus requires an equivalent number of random walks of length O(log n) each. A number of works have relied on the Chernoff bound to analytically reduce the overhead needed to obtain a multitude of uniform samples. Besides, researchers have also shown that it is not necessary to replicate both data and query on uniformly chosen nodes. Alternatively, BubbleStorm performs controlled flooding on a constructed overlay to build PBQS. BubbleStorm does not require nodes forming a bubble to be uniformly chosen at random, and the probabilistic bound computed by BubbleStorm is different from uniform sampling based PBQS. In this thesis, we first show that the Chernoff bound on the statistical properties of samples collected from a random walk does not help in selecting uniformly random nodes. We then re-examine the role of uniform sampling in PBQS, and found that when multiple data answer a single subscription, it is sufficient and necessary for each data to be distributed uniformly at random. Looking into BubbleStorm, we examine more closely the probabilistic bound provided by this system. We found that, unlike uniform sampling based PBQS, the bubble intersection in BubbleStorm is distance dependent. Given a specific pair of publisher-subscriber, the data may never find the subscription. We further investigate the topology construction and found that re-creating topology prior to each controlled flooding or keeping topology with high degree of churn can help alleviate the distance dependency problem. We arrive at the conclusion that BubbleStorm construction is equivalent to caching of random walks. We show that re-using this cache to obtain samples over time leads to degradation of uniformity of the samples. We evaluate topology re-wiring as a simple method to keep the cache fresh, thereby benefiting from the low latency of controlled flooding without degrading the uniformity of samples over time. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Peer-to-peer (p2p) approaches are an increasingly effective way to deploy services. Popular examples include BitTorrent, Skype, and KaZaA. These approaches are attractive because they can be highly fault-tolerant, scalable, adaptive, and less expensive than a more centralized solution. Cooperation lies at the heart of these strengths. Yet, in settings where working together is crucial, a natural question is: "What if users stop cooperating?" After all, cooperative services are typically deployed over multiple administrative domains, and thus vulnerable to Byzantine failures and users who may act selfishly. This dissertation explores how to construct p2p systems to tolerate Byzantine participants while also incentivizing selfish participants to contribute resources. We describe how to balance obedience against choice in building a robust p2p live streaming system. Imposing obedience is desirable as it leaves little room for peers to attack or cheat the system. However, providing choice is also attractive as it allows us to engineer flexible and efficient solutions. We first focus on obedience by using Nash equilibria to drive the design of BAR Gossip, the first gossip protocol that is resilient to Byzantine and selfish nodes. BAR Gossip relies on verifiable pseudo-random partner selection to eliminate non-determinism, which can be used to game the system, while maintaining the robustness and rapid convergence of traditional gossip. A novel fair enough exchange primitive entices cooperation among selfish peers on short timescales, thereby avoiding the need for distributed reputation schemes. We next focus on tempering obedience with choice by using approximate equilibria to guide the construction of a novel p2p live streaming system. These equilibria allow us to design incentives to limit selfish behavior rigorously, yet provide sufficient flexibility to build practical systems. We show the advantages of using an [element of]-Nash equilibrium, instead of an exact Nash, to design and implement FlightPath, our live streaming system that uses bandwidth efficiently, absorbs flash crowds, adapts to sudden peer departures, handles churn, and tolerates malicious activity. / text

Detta är en kvalitativ studie som syftar till att undersöka i vilken utsträckning ett finansiellt gap ligger till grund för svenska företags användning av lånebaserad crowdfunding, även kallat peer-to-peer-lån. Vidare syftar studien till att kartlägga svenska företags erfarenheter av peer-to-peer-lån i form av dess för- samt nackdelar. Undersökningen utgår från åtta svenska företag med olika erfarenheter av finansieringsverktyget. Som kompletterande empirikälla genomfördes också en intervju med en representant från en av de svenska storbankerna. Studiens teoretiska referensram består dels utav teorier som syftar till att ge en bakgrund till varför företag föredrar att finansiera sig med lån framför externt ägarkapital samt svenska SME’s problematiska förutsättningar för att få banklån. Vidare utgår uppsatsen från tidigare studier på ämnena peer-to-peer-lån och crowdfunding. Studiens slutsats visar på att det i vissa fall förefaller vara ett finansiellt gap som ligger till grund för svenska företags användning av peer-to-peer-lån. Marknadsföring, möjligheten att slippa banken samt att det är ett billigare finansieringsalternativ utgör ytterligare motiv som får företag att välja peer-to-peer-lån som finansieringsverktyg. Fler för- och nackdelar med peer-to-peer-lån identifieras genom studiens intervjuer med de svenska företagen som använt sig av finansieringsverktyget. Att processen är snabb och enkel samt att den ställer lägre krav vid ansökan om kapital jämfört med andra finansieringsverktyg är de två fördelar som flest respondenter i studien uttryckte med peer-to-peer-lån. Att peer-to-peer-lån är ett offentligt finansieringsverktyg var den nackdel som upplevdes som störst för det företag som medverkade i uppsatsens undersökning.

M. Tech. Electrical Engineering. / The demand for mobile telecommunication services has led to the rapid evolution, development and deployment of various technologies into the market. Communities and business customers demands for data, voice, video distribution, gaming and video conferencing are on the increase and peer-to-peer networks can play a major role in the sharing of content. An influx of various handheld devices such as smartphones and personal digital assistants (PDAs) into the market, augmented by the already available communication devices such as laptops and personal computers, has created a huge network of distributed devices. In this research, a community based mobile file-sharing system that can be used by groups of common interests such as tourists, farmers or students in a mobile peer-to-peer environment, is studied, designed and implemented.

This dissertation is an investigation into the practice of peer-to-peer file-sharing and the litigation campaign targeting individual file-sharers carried out by the Recording Industry Association of America (RIAA) from 2003 to 2008. The competing conceptualizations of social relations which motivate the conflict over peer-to-peer file-sharing are explored using a combination of Autonomist Marxist theory and structuration theory. Peer-to-peer file-sharing is framed as part of the social system of commoning stemming from the recent ascendancy of immaterial labor within that sector of the economy dedicated to the production and distribution of informational and cultural goods. The RIAA litigation campaign is framed as a reaction to the emergence of new forms of social relations which are seen by the content-producing industries as subversive of revenue streams premised on commodity exchange in informational and cultural goods. The history of the RIAA litigation campaign is presented in detail with careful attention given to those instances in which defendants and other interested parties fought back against RIAA legal actions. The acts of resistance within the legal arena affected the ultimate potential of the litigation campaign to control the spread of file-sharing activities. Subsequent legal campaigns which have been based on the RIAA litigation model are also examined. These later file-sharing cases have been met with similar forms of resistance which have likewise mitigated the impact of legal efforts to combat file-sharing. In addition, a survey of file-sharers is included in this research as part of an attempt to understand the relationship between legal actions targeting peer-to-peer systems and individual file-sharers and the technological and social development of peer-to-peer systems. This research argues that file-sharing litigation has proven ineffective in turning back the flood of file-sharing and may have increased the technological sophistication and community ties among file-sharers. In the end, the conflict over peer-to-peer file-sharing is cast as a manifestation of a larger dynamic of capitalist crisis as content-producing industries attempt to come to terms with the contradictory tendencies of immaterial labor and the production of common pools of digital resources. / text

Η τεχνολογία ‘p2p’ είναι μια αρκετά υποσχόμενη τεχνολογία που έχει τραβήξει το ενδιαφέρον των ερευνητών της Πληροφορικής τα τελευταία χρόνια. Σε μεγάλο βαθμό το έναυσμα έδωσε η δημοφιλής εφαρμογή ‘Napster’ διαμοίρασης αρχείων μουσικής στο Διαδίκτυο (1999). Σήμερα τα συστήματα που έχουν αναπτυχθεί τόσο εμπορικά όσο και ακαδημαϊκά, καλύπτουν εύρος εφαρμογών όπως συνεργατικότητα, βιοπληροφορική, διαχείρηση περιεχομένου, εταιρική διαχείριση δεδομένων και είναι αρκετά πιο πολύπλοκα. Τα συστήματα αυτά μπορούν να διακριθούν κατά κύριο λόγο σε αδόμητα και δομημένα. Τα αδόμητα αποτελούν την πρώτη γενιά και τα δομημένα τη δεύτερη γενιά συστημάτων p2p. Η βασική διαφορά των δύο κατηγοριών είναι ότι στα δομημένα συστήματα, το δίκτυο επικάλυψης (overlay network) που αυτά υλοποιούν, επιβάλει μια εικονική τοπολογία των κόμβων του δικτύου πάνω από τη φυσική. Μέσω της εικονικής τοπολογίας υλοποιείται συνήθως μια κατανεμημένη δομή δεικτοδότητησης. Το βασικό όφελος των δομημένων συστημάτων είναι το φραγμένο κόστος στην εκτέλεση των λειτουργιών της δομής το οποίο μετράται ως ο αριθμός των βημάτων που εκτελούνται στην εικονική τοπολογία. Αντίθετα στα αδόμητα συστήματα p2p ένας κόμβος εισάγεται τυχαία και οι λειτουργίες του δικτύου εκτελούνται συνήθως με πρωτόκολλα πλημμυρίδας μικρής εμβέλειας ή τυχαίους περιπάτους. Δημοφιλή συστήματα δομημένων συστημάτων είναι τα ακόλουθα: Chord, Can, Pastry, Tapestry, Kademlia, Koorde, Baton*, Skip Graphs, Family Trees. Ωστόσο τα περισσότερα συστήματα p2p αγνοούν την υπάρχουσα φυσική τοπολογία με αποτέλεσμα να μην υπάρχουν εγγυήσεις ως προς την πραγματική καθυστέρηση. Στην παρούσα μεταπτυχιακή εργασία μελετώνται και αξιολογούνται μηχανισμοί ενσωμάτωσης της πληροφορίας της φυσικής τοπολογίας για τα τρέχοντα δομημένα δίκτυα p2p πάνω από το Διαδίκτυο καθώς και νέα συστήματα προσανατολισμένα προς την εκμετάλλευση της φυσικής πληροφορίας (τρίτη γενιά). Επιπλέον στο πλαίσιο της εργασίας αυτής προτείνεται ένα νέο, δομημένο σύστημα p2p βασισμένο τον πλήρη γράφο μεταθέσεων. Το σύστημα υλοποιήθηκε και αξιολογήθηκε ως προς την απόδοση του. / Peer-to-peer technology is a very promising technology which has drawn the interest of the research community for the past few years. The major cause for the boost of this research area was Napster (1999), a popular music file-sharing application. Today p2p systems, both commercial and academic, are rather complicated and implement various applications such as bioinformatics, content management, collaboration etc. There are to major categories of p2p systems: unstructured and structured p2p systems. Unstructured p2p systems constitute the first generation of p2p systems while structured p2p systems constitute the second one. The difference of these two categories is that structured p2p systems implement a virtual overlay network which imposes a virtual topology over the physical network topology. Based on this topology structured p2p systems implement a distributed indexing structure. The advantage of the structured p2p systems is that the indexing structure exhibits bounded cost for its operations. In contrast to structured p2p systems, in unstructured p2p systems, network operations are executed by flooding protocols or random walks. Widely known structured p2p systems are the following: Chord, Can, Pastry, Tapestry, Kademlia, Koorde, Baton*, Skip-Graphs, Family Trees. However, most p2p systems ignore the underlying physical topology. Consequently, p2p systems give no guaranties for the actual network delay. In this thesis we investigate mechanisms for the exploitation of the information of the physical topology in current p2p systems over the Internet. Moreover, we present recent systems that embed in their design the information of the physical topology (third generation of p2p systems). Finally, we present a novel structured p2p system based on the full transposition graph. Our system was both implemented and evaluated for its performance.

Durant la última dècada, la demanda d’emmagatzematge de dades ha anat creixent exponencialment any rere any. Apart de demanar més capacitat d’emmagatzematge, el usuaris actualment també demanen poder accedir a les seves dades des de qualsevol lloc i des de qualsevol dispositiu. Degut a aquests nous requeriments, els usuaris estan actualment movent les seves dades personals (correus electrònics, documents, fotografies, etc.) cap a serveis d’emmagatzematge en línia com ara Gmail, Facebook, Flickr o Dropbox. Malauradament, aquests serveis d’emmagatzematge en línia estan sostinguts per unes grans infraestructures informàtiques que poques empreses poden finançar. Per tal de reduir el costs d’aquestes grans infraestructures informàtiques, ha sorgit una nova onada de serveis d’emmagatzematge en línia que obtenen grans infraestructures d’emmagatzematge a base d’integrar els recursos petits centres de dades, o fins i tot a base d’integrar els recursos d’emmagatzematge del usuaris finals. No obstant això, els recursos que formen aquestes noves infraestructures d’emmagatzematge són molt heterogenis, cosa que planteja un repte per al dissenyadors d’aquests sistemes: Com es poden dissenyar sistemes d’emmagatzematge en línia, fiables i eficients, quan la infraestructura emprada és tan heterogènia? Aquesta tesis presenta un estudi dels principals problemes que sorgeixen quan un vol respondre a aquesta pregunta. A més proporciona diferents eines per tal d’optimitzar el disseny de sistemes d’emmagatzematge distribuïts i heterogenis. Les principals contribucions són: Primer, creem un marc d’anàlisis per estudiar els efectes de la redundància de dades en el cost dels sistemes d’emmagatzematge distribuïts. Donat un esquema de redundància específic, el marc d’anàlisis presentat permet predir el cost mitjà d’emmagatzematge i el cost mitjà de comunicació d’un sistema d’emmagatzematge implementat sobre qualsevol infraestructura informàtica distribuïda. Segon, analitzem els impactes que la redundància de dades té en la disponibilitat de les dades, i en els temps de recuperació. Donada una redundància, i donat un sistema d’emmagatzematge heterogeni, creem un grup d’algorismes per a determinar la disponibilitat de les dades esperada, i els temps de recuperació esperats. Tercer, dissenyem diferents polítiques d’assignació de dades per a diferents sistemes d’emmagatzematge. Diferenciem entre aquells escenaris on la totalitat de la infraestructura està administrada per una sola organització, i els escenaris on diferents parts auto administrades contribueixen els seus recursos. Els objectius de les nostres polítiques d’assignació de dades són: (i) minimitzar la redundància necessària, (ii) garantir la equitat entre totes les parts que participen al sistema, i (iii) incentivar a les parts perquè contribueixin els seus recursos al sistema. / Over the last decade, users’ storage demands have been growing exponentially year over year. Besides demanding more storage capacity and more data reliability, today users also demand the possibility to access their data from any location and from any device. These new needs encourage users to move their personal data (e.g., E-mails, documents, pictures, etc.) to online storage services such as Gmail, Facebook, Flickr or Dropbox. Unfortunately, these online storage services are built upon expensive large datacenters that only a few big enterprises can afford. To reduce the costs of these large datacenters, a new wave of online storage services has recently emerged integrating storage resources from different small datacenters, or even integrating user storage resources into the provider’s storage infrastructure. However, the storage resources that compose these new storage infrastructures are highly heterogeneous, which poses a challenging problem to storage systems designers: How to design reliable and efficient distributed storage systems over heterogeneous storage infrastructures? This thesis provides an analysis of the main problems that arise when one aims to answer this question. Besides that, this thesis provides different tools to optimize the design of heterogeneous distributed storage systems. The contribution of this thesis is threefold: First, we provide a novel framework to analyze the effects that data redundancy has on the storage and communication costs of distributed storage systems. Given a generic redundancy scheme, the presented framework can predict the average storage costs and the average communication costs of a storage system deployed over a specific storage infrastructure. Second, we analyze the impacts that data redundancy has on data availability and retrieval times. For a given redundancy and a heterogeneous storage infrastructure, we provide a set of algorithms that allow to determine the expected data availability and expected retrieval times. Third, we design different data assignment policies for different storage scenarios. We differentiate between scenarios where the entire storage infrastructure is managed by the same organization, and scenarios where different parties contribute their storage resources. The aims of our assignment policies are: (i) to minimize the required redundancy, (ii) to guarantee fairness among all parties, and (iii) to encourage different parties to contribute their local storage resources to the system.

Trust is required in file sharing peer-to-peer (P2P) systems to achieve better cooperation among peers and reduce malicious uploads. In reputation-based P2P systems, reputation is used to build trust among peers based on their past transactions and feedbacks from other peers. In these systems, reputable peers will usually be selected to upload requested files, decreasing significantly malicious uploads in the system. This thesis surveys different reputation management systems with a focus on reputation based P2P systems. We breakdown a typical reputation system into functional components. We discuss each component and present proposed solutions from the literature. Different reputation-based systems are described and analyzed. Each proposed scheme presents a particular perspective in addressing peers’ reputation. This thesis also presents a novel trust management framework and associated schemes for partially decentralized file sharing P2P systems. We address trust according to three identified dimensions: Authentic Behavior, Credibility Behavior and Contribution Behavior. Within our trust management framework, we proposed several algorithms for reputation management. In particular, we proposed algorithms to detect malicious peers that send inauthentic files, and liar peers that send wrong feedbacks. Reputable peers need to be motivated to upload authentic files by increasing the benefits received from the system. In addition, free riders need to contribute positively to the system. These peers are consuming resources without uploading to others. To provide the right incentives for peers, we develop a novel service differentiation scheme based on peers’ contribution rather than peers’ reputation. The proposed scheme protects the system against free-riders and malicious peers and reduces the service provided to them. In this thesis, we also propose a novel recommender framework for partially decentralized file sharing P2P systems. We take advantage from the partial search process used in these systems to explore the relationships between peers. The proposed recommender system does not require any additional effort from the users since implicit rating is used. The recommender system also does not suffer from the problems that affect traditional collaborative filtering schemes like the Cold start, the Data sparseness and the Popularity effect. Over all, our unified approach to trust management and recommendations allows for better system health and increased user satisfaction.

Given a set of peers with overlapping interests where each peer wishes to keep track of new documents that are relevant to their interests, we propose Shrack-a self-organizing peer-to-peer (P2P) system for document sharing and tracking. The goal of a document-tracking system is to disseminate new documents as they are published. We present a framework of Shrack and propose a gossip-like pull-only information dissemination protocol. We explore and develop mechanisms to enable a self-organizing network, based on common interest of document sets among peers. Shrack peers collaboratively share new documents of interest with other peers. Interests of peers are modeled using relevant document sets and are represented as peer profiles. There is no explicit pro file exchange between peers and no global information available. We describe how peers create their user pro files, discover the existence of other peers, locally learn about interest of other peers, and finally form a self-organizing overlay network of peers with common interests. Unlike most existing P2P file sharing systems which serve their users by finding relevant documents based on an instant query, Shrack is designed to help users that have long-term interests to keep track of relevant documents that are newly available in the system. The framework can be used as an infrastructure for any kind of documents and data, but in this thesis, we focus on research publications. We built an event-driven simulation to evaluate the performance and behaviour of Shrack. We model simulated users associated with peers after a subset of authors in the ACM digital library metadata collection. The experimental results demonstrate that the Shrack dissemination protocol is scalable as the network size increases. In addition, self-organizing overlay networks, where connections between peers are based on common interests as captured by their associated document sets, can help improve the relevance of documents received by peers in terms of F-score over random peer networks. Moreover, the resulting self-organizing networks have the characteristics of social networks.