Página 16 dos resultados de 686 itens digitais encontrados em 0.002 segundos

## Arquitetura de IPTV com suporte à apresentação deslocada no tempo baseada em distribuição peer-to-peer.; IPTV architecture with time-shift support based on peer-to-peer distribution.

Gallo, Diego Sanchez
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Um modelo arquitetural para captura e uso de informações de contexto em sistemas de anotações de vídeo; An architectural model to capture and use context information in video annotation systems

Fagá Júnior, Roberto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Algoritmo de escalonamento para aplicações em uma grade computacional extensível aos receptores de sinais digitais de televisão; Scheduling algorithm for applications in a computational grid extensible to receivers of television digital signal

Batista, Bruno Guazzelli
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
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## EbitSim: simulador de BitTorrent utilizando o arcabouço OMNeT++.; EbitSim: BitTorrent simulator using the OMNeT++ framework.

Evangelista, Pedro Manoel Fabiano Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Stochastic Analysis of a Churn-Tolerant Structured Peer-to-Peer Scheme

Jacobs, Tim; Pandurangan, Gopal
Tipo: Artigo de Revista Científica
Português
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We present and analyze a simple and general scheme to build a churn (fault)-tolerant structured Peer-to-Peer (P2P) network. Our scheme shows how to "convert" a static network into a dynamic distributed hash table(DHT)-based P2P network such that all the good properties of the static network are guaranteed with high probability (w.h.p). Applying our scheme to a cube-connected cycles network, for example, yields a $O(\log N)$ degree connected network, in which every search succeeds in $O(\log N)$ hops w.h.p., using $O(\log N)$ messages, where $N$ is the expected stable network size. Our scheme has an constant storage overhead (the number of nodes responsible for servicing a data item) and an $O(\log N)$ overhead (messages and time) per insertion and essentially no overhead for deletions. All these bounds are essentially optimal. While DHT schemes with similar guarantees are already known in the literature, this work is new in the following aspects: (1) It presents a rigorous mathematical analysis of the scheme under a general stochastic model of churn and shows the above guarantees; (2) The theoretical analysis is complemented by a simulation-based analysis that validates the asymptotic bounds even in moderately sized networks and also studies performance under changing stable network size; (3) The presented scheme seems especially suitable for maintaining dynamic structures under churn efficiently. In particular...

## Multiplayer Games and their Need for Scalable and Secure State Management

Alomari, Zakaria
Tipo: Artigo de Revista Científica
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In recent years, massively multiplayer online games (MMOGs) have become very popular by providing more entertainment, therefore millions of players now participate may interact with each other in a shared environment, even though these players may be separated by huge geographic distances. Peer to Peer (P2P) architectures become very popular in MMOG recently, due to their distributed and collaborative nature, have low infrastructure costs, achieve fast response times by creating direct connections between players and can achieve high scalability. However, P2P architectures face many challenges and tend to be vulnerable to cheating. Game distribution between peers makes maintaining control of the game becomes more complicated. Therefore, broadcasting all state changes to every player is not a viable solution to maintain a consistent game state in a MMOGs. To successfully overcome the challenge of scale, MMOGs have to employ sophisticated interest management techniques that only send relevant state changes to each player. In this paper, In order to prevent cheaters to gain unfair advantages in P2P-based MMOGs, several cheat-proof schemes have been proposed that utilize a range of techniques such as cryptographic mechanisms, Commitment and agreement protocols...

## Diffusive Load Balancing of Loosely-Synchronous Parallel Programs over Peer-to-Peer Networks

Douglas, Scott; Harwood, Aaron
Tipo: Artigo de Revista Científica
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The use of under-utilized Internet resources is widely recognized as a viable form of high performance computing. Sustained processing power of roughly 40T FLOPS using 4 million volunteered Internet hosts has been reported for embarrassingly parallel problems. At the same time, peer-to-peer (P2P) file sharing networks, with more than 50 million participants, have demonstrated the capacity for scale in distributed systems. This paper contributes a study of load balancing techniques for a general class of loosely-synchronous parallel algorithms when executed over a P2P network. We show that decentralized, diffusive load balancing can be effective at balancing load and is facilitated by the dynamic properties of P2P. While a moderate degree of dynamicity can benefit load balancing, significant dynamicity hinders the parallel program performance due to the need for increased load migration. To the best of our knowledge this study provides new insight into the performance of loosely-synchronous parallel programs over the Internet.; Comment: 14 pages with 10 figures

## Optimal Scheduling of Peer-to-Peer File Dissemination

Mundinger, Jochen; Weber, Richard R.; Weiss, Gideon
Tipo: Artigo de Revista Científica
Português
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## Interference Alignment and Neutralization in a Cognitive 3-User MAC-Interference Channel: Degrees of Freedom

Chaaban, Anas; Sezgin, Aydin
Tipo: Artigo de Revista Científica
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A network consisting of a point-to-point (P2P) link and a multiple access channel (MAC) sharing the same medium is considered. The resulting interference network, with three transmitters and two receivers is studied from degrees of freedom (DoF) perspective, with and without cognition. Several cognition variants are examined. Namely, the setup is studied with (1) no cognitive transmitters, (2) a cognitive P2P transmitter, (3) one cognitive MAC transmitter, and (4) with two cognitive MAC transmitters. It is shown that having a cognitive P2P transmitter does not bring any DoF gain to the network. This is obtained by showing that the DoF of the two former cases (1) and (2) is 1. However, it is shown that a cognitive MAC transmitter is more beneficial since the latter two cases (3) and (4) have 3/2 DoF. The achievability of 3/2 DoF is guaranteed by using a combination of interference neutralization and interference alignment.; Comment: 4 pages, 1 figure, presented at the CWIT 2011

## Virtual Private Overlays: Secure Group Commounication in NAT-Constrained Environments

Wolinsky, David Isaac; Lee, Kyungyong; Choi, Tae Woong; Boykin, P. Oscar; Figueiredo, Renato
Tipo: Artigo de Revista Científica
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Structured P2P overlays provide a framework for building distributed applications that are self-configuring, scalable, and resilient to node failures. Such systems have been successfully adopted in large-scale Internet services such as content delivery networks and file sharing; however, widespread adoption in small/medium scales has been limited due in part to security concerns and difficulty bootstrapping in NAT-constrained environments. Nonetheless, P2P systems can be designed to provide guaranteed lookup times, NAT traversal, point-to-point overlay security, and distributed data stores. In this paper we propose a novel way of creating overlays that are both secure and private and a method to bootstrap them using a public overlay. Private overlay nodes use the public overlay's distributed data store to discover each other, and the public overlay's connections to assist with NAT hole punching and as relays providing STUN and TURN NAT traversal techniques. The security framework utilizes groups, which are created and managed by users through a web based user interface. Each group acts as a Public Key Infrastructure (PKI) relying on the use of a centrally-managed web site providing an automated Certificate Authority (CA). We present a reference implementation which has been used in a P2P VPN (Virtual Private Network). To evaluate our contributions...

## Performance Analysis of Publish/Subscribe Systems

Abbes, Heithem; Cérin, Christophe; Dubacq, Jean-Christophe; Jemni, Mohamed
Tipo: Artigo de Revista Científica
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The Desktop Grid offers solutions to overcome several challenges and to answer increasingly needs of scientific computing. Its technology consists mainly in exploiting resources, geographically dispersed, to treat complex applications needing big power of calculation and/or important storage capacity. However, as resources number increases, the need for scalability, self-organisation, dynamic reconfigurations, decentralisation and performance becomes more and more essential. Since such properties are exhibited by P2P systems, the convergence of grid computing and P2P computing seems natural. In this context, this paper evaluates the scalability and performance of P2P tools for discovering and registering services. Three protocols are used for this purpose: Bonjour, Avahi and Free-Pastry. We have studied the behaviour of theses protocols related to two criteria: the elapsed time for registrations services and the needed time to discover new services. Our aim is to analyse these results in order to choose the best protocol we can use in order to create a decentralised middleware for desktop grid.

## Combining Peer-to-Peer and Cloud Computing for Large Scale On-line Games

Carlini, Emanuele
Tipo: Artigo de Revista Científica
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This thesis investigates the combination of Peer-to-Peer (P2P) and Cloud Computing to support Massively Multiplayer On- line Games (MMOGs). MMOGs are large-scale distributed applications where a large number of users concurrently share a real-time virtual environment. Commercial MMOG infrastructures are sized to support peak loads, incurring in high economical cost. Cloud Computing represents an attractive solution, as it lifts MMOG operators from the burden of buying and maintaining hardware, while offering the illusion of infinite machines. However, it requires balancing the tradeoff between resource provisioning and operational costs. P2P- based solutions present several advantages, including the inherent scalability, self-repairing, and natural load distribution capabilities. They require additional mechanisms to suit the requirements of a MMOG, such as backup solutions to cope with peer unreliability and heterogeneity. We propose mechanisms that integrate P2P and Cloud Computing combining their advantages. Our techniques allow operators to select the ideal tradeoff between performance and economical costs. Using realistic workloads, we show that hybrid infrastructures can reduce the economical effort of the operator, while offering a level of service comparable with centralized architectures.

## Complex networks: A mixture of power-law and Weibull distributions

Xu, Ke; Liu, Liandong; Liang, Xiao
Tipo: Artigo de Revista Científica
Português
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Complex networks have recently aroused a lot of interest. However, network edges are considered to be the same in almost all these studies. In this paper, we present a simple classification method, which divides the edges of undirected, unweighted networks into two types: p2c and p2p. The p2c edge represents a hierarchical relationship between two nodes, while the p2p edge represents an equal relationship between two nodes. It is surprising and unexpected that for many real-world networks from a wide variety of domains (including computer science, transportation, biology, engineering and social science etc), the p2c degree distribution follows a power law more strictly than the total degree distribution, while the p2p degree distribution follows the Weibull distribution very well. Thus, the total degree distribution can be seen as a mixture of power-law and Weibull distributions. More surprisingly, it is found that in many cases, the total degree distribution can be better described by the Weibull distribution, rather than a power law as previously suggested. By comparing two topology models, we think that the origin of the Weibull distribution in complex networks might be a mixture of both preferential and random attachments when networks evolve.; Comment: 5 pages...

## SecMon: End-to-End Quality and Security Monitoring System

Ciszkowski, Tomasz; Eliasson, Charlott; Fiedler, Markus; Kotulski, Zbigniew; Lupu, Radu; Mazurczyk, Wojciech
Tipo: Artigo de Revista Científica
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The Voice over Internet Protocol (VoIP) is becoming a more available and popular way of communicating for Internet users. This also applies to Peer-to-Peer (P2P) systems and merging these two have already proven to be successful (e.g. Skype). Even the existing standards of VoIP provide an assurance of security and Quality of Service (QoS), however, these features are usually optional and supported by limited number of implementations. As a result, the lack of mandatory and widely applicable QoS and security guaranties makes the contemporary VoIP systems vulnerable to attacks and network disturbances. In this paper we are facing these issues and propose the SecMon system, which simultaneously provides a lightweight security mechanism and improves quality parameters of the call. SecMon is intended specially for VoIP service over P2P networks and its main advantage is that it provides authentication, data integrity services, adaptive QoS and (D)DoS attack detection. Moreover, the SecMon approach represents a low-bandwidth consumption solution that is transparent to the users and possesses a self-organizing capability. The above-mentioned features are accomplished mainly by utilizing two information hiding techniques: digital audio watermarking and network steganography. These techniques are used to create covert channels that serve as transport channels for lightweight QoS measurement's results. Furthermore...

## Coalitional Graph Games for Popular Content Distribution in Cognitive Radio VANETs

Wang, Tianyu; Song, Lingyang; Han, Zhu
Tipo: Artigo de Revista Científica
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Popular content distribution is one of the key services provided by vehicular ad hoc networks (VANETs), in which a popular file is broadcasted by roadside units (RSUs) to the on-board units (OBUs) driving through a particular area. Due to fast speed and deep fading, some file packets might be lost during the vehicle-to-roadside broadcasting stage. In this paper, we propose a peer-to-peer (P2P) approach to allow the OBUs to exchange data and complement the missing packets. Specifically, we introduce a coalitional graph game to model the cooperation among OBUs and propose a coalition formation algorithm to implement the P2P approach. Moreover, cognitive radio is utilized for vehicle-to-vehicle transmissions so that the P2P approach does not require additional bandwidth. Simulation results show that the proposed approach performs better in various conditions, relative to the non-cooperative approach, in which the OBUs share no information and simply response to any data request from other OBUs.

## Distributed Slicing in Dynamic Systems

Fernandez, Antonio; Gramoli, Vincent; Jimenez, Ernesto; Kermarrec, Anne-Marie; Raynal, Michel
Tipo: Artigo de Revista Científica
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Peer to peer (P2P) systems are moving from application specific architectures to a generic service oriented design philosophy. This raises interesting problems in connection with providing useful P2P middleware services capable of dealing with resource assignment and management in a large-scale, heterogeneous and unreliable environment. The slicing service, has been proposed to allow for an automatic partitioning of P2P networks into groups (slices) that represent a controllable amount of some resource and that are also relatively homogeneous with respect to that resource. In this paper we propose two gossip-based algorithms to solve the distributed slicing problem. The first algorithm speeds up an existing algorithm sorting a set of uniform random numbers. The second algorithm statistically approximates the rank of nodes in the ordering. The scalability, efficiency and resilience to dynamics of both algorithms rely on their gossip-based models. These algorithms are proved viable theoretically and experimentally.

## Designing ISP-friendly Peer-to-Peer Networks Using Game-based Control

Reddy, Vinith; Kim, Younghoon; Shakkottai, Srinivas; Reddy, A. L. Narasimha
Tipo: Artigo de Revista Científica
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The rapid growth of peer-to-peer (P2P) networks in the past few years has brought with it increases in transit cost to Internet Service Providers (ISPs), as peers exchange large amounts of traffic across ISP boundaries. This ISP oblivious behavior has resulted in misalignment of incentives between P2P networks--that seek to maximize user quality--and ISPs--that would seek to minimize costs. Can we design a P2P overlay that accounts for both ISP costs as well as quality of service, and attains a desired tradeoff between the two? We design a system, which we call MultiTrack, that consists of an overlay of multiple \emph{mTrackers} whose purpose is to align these goals. mTrackers split demand from users among different ISP domains while trying to minimize their individual costs (delay plus transit cost) in their ISP domain. We design the signals in this overlay of mTrackers in such a way that potentially competitive individual optimization goals are aligned across the mTrackers. The mTrackers are also capable of doing admission control in order to ensure that users who are from different ISP domains have a fair chance of being admitted into the system, while keeping costs in check. We prove analytically that our system is stable and achieves maximum utility with minimum cost. Our design decisions and control algorithms are validated by Matlab and ns-2 simulations.

## Extended Equal Service and Differentiated Service Models for Peer-to-Peer File Sharing

Zhang, Jianwei; Wang, Yongchao; Xing, Wei; Lu, Dongming
Tipo: Artigo de Revista Científica
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Peer-to-Peer (P2P) systems have proved to be the most effective and popular file sharing applications in recent years. Previous studies mainly focus on the equal service and the differentiated service strategies when peers have no initial data before their download. In an upload-constrained P2P file sharing system, we model both the equal service process and the differentiated service process when peers' initial data distribution satisfies some special conditions, and also show how to minimize the time to get the file to any number of peers. The proposed models can reveal the intrinsic relations among the initial data amount, the size of peer set and the minimum last finish time. By using the models, we can also provide arbitrary degree of differentiated service to a certain number of peers. We believe that our analysis process and achieved theoretical results could provide fundamental insights into studies on bandwidth allocation and data scheduling, and can give helpful reference both for improving system performance and building effective incentive mechanism in P2P file sharing systems.

## Detecting and recovering from overlay routing attacks in peer-to-peer distributed hash tables

Needels, Keith
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Português
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Distributed hash tables (DHTs) provide efficient and scalable lookup mechanisms for locating data in peer-to-peer (P2P) networks. A number of issues, however, prevent DHT based P2P networks from being widely deployed. One of these issues is security. DHT protocols rely on the users of the system to cooperate for lookup requests to successfully reach the correct destination. Users who fail to run the protocol correctly can severely limit the functionality of these systems. The fully distributed nature of DHTs compounds these security issues, as any security mechanism must be implemented in a noncentralized fashion for the system to remain truly P2P. This thesis examines the security issues facing DHT protocols, and we propose an extension to one such protocol (called Chord) to mitigate the effects of attacks on the underlying lookup message routing mechanism when a minority of nodes in the system are malicious. Our modifications require no trust to exist between nodes in the network except during the joining process. Instead, each node makes use of locally known information about the network to evaluate hops encountered during the lookup routing process for validity. Hops that are determined to be invalid are avoided. These modifications to the Chord protocol have been implemented in a simulator and then evaluated in the presence of malicious nodes. We present the results of this evaluation and compare them to the results obtained when running the unmodified Chord protocol.

## Secure routing in peer-to-peer distributed hash tables

Needels, Keith; Kwon, Minseok
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Proceedings
Português
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Distributed hash tables (DHTs) provide efficient and scalable look up mechanisms for locating data in peer-to-peer (p2p) networks. Several issues, however, prevent DHT-based p2p networks from being widely deployed – one of which is security. Malicious peers may modify, drop, misroute lookup requests, or even collude to deny the availability of target data. To address these security concerns, we propose an extension to Chord named Sechord. The main idea is that the source can determine whether the next hop is valid or invalid by estimating how far the next hop is from its finger pointer. If the next hop is too far away from the finger pointer, especially compared to the average distance between two consecutive peers, the source can infer some ongoing malicious activities. Our modifications require no trust between two nodes except node join. Moreover, each node utilizes locally available information to evaluate hops encountered during the lookup routing process for validity. These modifications have been implemented and evaluated in the presence of malicious nodes. Our results show that Sechord significantly enhances the security of structured p2p systems at the expense of slightly increased hop count.; To appear in the ACM Symposium on Applied Computing (SAC)...