869 research outputs found
Fine Grained Component Engineering of Adaptive Overlays: Experiences and Perspectives
Recent years have seen significant research being carried out into peer-to-peer (P2P) systems. This work has focused on the styles and applications of P2P computing, from grid computation to content distribution; however, little investigation has been performed into how these systems are built. Component based engineering is an approach that has seen successful deployment in the field of middleware development; functionality is encapsulated in âbuilding blocksâ that can be dynamically plugged together to form complete systems. This allows efficient, flexible and adaptable systems to be built with lower overhead and development complexity. This paper presents an investigation into the potential of using component based engineering in the design and construction of peer-to-peer overlays. It is highlighted that the quality of these properties is dictated by the component architecture used to implement the system. Three reusable decomposition architectures are designed and evaluated using Chord and Pastry case studies. These demonstrate that significant improvements can be made over traditional design approaches resulting in much more reusable, (re)configurable and extensible systems
Socially-Aware Distributed Hash Tables for Decentralized Online Social Networks
Many decentralized online social networks (DOSNs) have been proposed due to
an increase in awareness related to privacy and scalability issues in
centralized social networks. Such decentralized networks transfer processing
and storage functionalities from the service providers towards the end users.
DOSNs require individualistic implementation for services, (i.e., search,
information dissemination, storage, and publish/subscribe). However, many of
these services mostly perform social queries, where OSN users are interested in
accessing information of their friends. In our work, we design a socially-aware
distributed hash table (DHTs) for efficient implementation of DOSNs. In
particular, we propose a gossip-based algorithm to place users in a DHT, while
maximizing the social awareness among them. Through a set of experiments, we
show that our approach reduces the lookup latency by almost 30% and improves
the reliability of the communication by nearly 10% via trusted contacts.Comment: 10 pages, p2p 2015 conferenc
Cross-layer Peer-to-Peer Computing in Mobile Ad Hoc Networks
The future information society is expected to rely heavily on wireless technology. Mobile access to the Internet is steadily gaining ground, and could easily end up exceeding the number of connections from the fixed infrastructure. Picking just one example, ad hoc networking is a new paradigm of wireless communication for mobile devices. Initially, ad hoc networking targeted at military applications as well as stretching the access to the Internet beyond one wireless hop. As a matter of fact, it is now expected to be employed in a variety of civilian applications. For this reason, the issue of how to make these systems working efficiently keeps the ad hoc research community active on topics ranging from wireless technologies to networking and application systems.
In contrast to traditional wire-line and wireless networks, ad hoc networks are expected to operate in an environment in which some or all the nodes are mobile, and might suddenly disappear from, or show up in, the network. The lack of any centralized point, leads to the necessity of distributing application services and responsibilities to all available nodes in the network, making the task of developing and deploying application a hard task, and highlighting the necessity of suitable middleware platforms.
This thesis studies the properties and performance of peer-to-peer overlay management algorithms, employing them as communication layers in data sharing oriented middleware platforms. The work primarily develops from the observation that efficient overlays have to be aware of the physical network topology, in order to reduce (or avoid) negative impacts of application layer traffic on the network functioning. We argue that cross-layer cooperation between overlay management algorithms and the underlying layer-3 status and protocols, represents a viable alternative to engineer effective decentralized communication layers, or eventually re-engineer existing ones to foster the interconnection of ad hoc networks with Internet infrastructures. The presented approach is twofold. Firstly, we present an innovative network stack component that supports, at an OS level, the realization of cross-layer protocol interactions. Secondly, we exploit cross-layering to optimize overlay management algorithms in unstructured, structured, and publish/subscribe platforms
Search strategies in unstructured overlays
Trabalho de projecto de mestrado em Engenharia InformĂĄtica, apresentado Ă Universidade de Lisboa, atravĂ©s da Faculdade de CiĂȘncias, 2008Unstructured peer-to-peer networks have a low maintenance cost, high resilience and tolerance to the continuous arrival and departure of nodes. In these networks search is usually performed by flooding, which generates a high number of duplicate messages. To improve scalability, unstructured overlays evolved to a two-tiered architecture where regular nodes rely on special nodes, called supernodes or superpeers, to locate resources, thus reducing the scope of flooding based searches. While this approach takes advantage of node heterogeneity, it makes the overlay less resilient to accidental and malicious faults, and less attractive to users concerned with the consumption of their resources and who may not desire to commit additional resources that are required by nodes selected as superpeers. Another point of concern is churn, defined as the constant entry and departure of nodes. Churn affects both structured and unstructured overlay networks and, in order to build resilient search protocols, it must be taken into account. This dissertation proposes a novel search algorithm, called FASE, which combines a replication policy and a search space division technique to achieve low hop counts using a small number of messages, on unstructured overlays with nonhierarquical topologies. The problem of churn is mitigated by a distributed monitoring algorithm designed with FASE in mind. Simulation results validate FASE efficiency when compared to other search algorithms for peer-to-peer networks. The evaluation of the distributed monitoring algorithm shows that it maintains FASE performance when subjected to churn.Os sistemas peer-to-peer, como aplicaçÔes de partilha e distribuição de conteĂșdos ou voz-sobre-IP, sĂŁo construĂdos sobre redes sobrepostas. Redes sobrepostas sĂŁo redes virtuais que existem sobre uma rede subjacente, em que a topologia da rede sobreposta nĂŁo tem de ter uma correspondĂȘncia com a topologia da rede subjacente. Ao contrĂĄrio das suas congĂ©neres estruturadas, as redes sobrepostas nĂŁo-estru-turadas nĂŁo restringem a localização dos seus participantes, ou seja, nĂŁo limitam a escolha de vizinhos de um dado nĂł, o que torna a sua manutenção mais simples. O baixo custo de manutenção das redes sobrepostas nĂŁo-estruturadas torna estas especialmente adequadas para a construção de sistemas peer-to-peer capazes de tolerar o comportamento dinĂąmico dos seus participantes, uma vez que estas redes sĂŁo permanentemente afectadas pela entrada e saĂda de nĂłs na rede, um fĂ©nomeno conhecido como churn. O algoritmo de pesquisa mais comum em redes sobrepostas nĂŁo-estruturadas consiste em inundar a rede, o que origina uma grande quantidade de mensagens duplicadas por cada pesquisa. A escalabilidade destes algoritmos Ă© limitada porque consomem demasiados recursos da rede em sistemas com muitos participantes. Para reduzir o nĂșmero de mensagens, as redes sobrepostas nĂŁo-estruturadas podem ser organizadas em topologias hierĂĄrquicas. Nestas topologias alguns nĂłs da rede, chamados supernĂłs, assumem um papel mais importante, responsabilizando-se pela localização de objectos. A utilização de supernĂłs cria novos problemas, como a sua selecção e a dependĂȘncia da rede de uma pequena percentagem dos nĂłs. Esta dissertação apresenta um novo algoritmo de pesquisa, chamado FASE, criado para operar sobre redes sobrepostas nĂŁo estruturadas com topologias nĂŁo-hierĂĄrquicas. Este algoritmo combina uma polĂtica de replicação com uma tĂ©cnica de divisĂŁo do espaço de procura para resolver pesquisas ao alcançe de um nĂșmero reduzido de saltos com o menor custo possĂvel. Adicionalmente, o algoritmo procura nivelar a contribuição dos participantes, jĂĄ que todos contribuem de uma forma semelhante para o desempenho da pesquisa. A estratĂ©gia seguida pelo algo- ritmo consiste em dividir tanto os nĂłs da rede como as chaves dos seus conteĂșdos por diferentes âfrequĂȘnciasâ e replicar chaves nas respectivas frequĂȘncias, sem, no entanto, limitar a localização de um nĂł ou impor uma estrutura Ă rede ou mesmo aplicar uma definição rĂgida de chave. Com o objectivo de mitigar o problema do churn, Ă© apresentado um algoritmo de monitorização distribuĂdo para as rĂ©plicas originadas pelo FASE. Os algoritmos propostos sĂŁo avaliados atravĂ©s de simulaçÔes, que validam a eficiĂȘncia do FASE quando comparado com outros algoritmos de pesquisa em redes sobrepostas nĂŁo-estruturadas. Ă tambĂ©m demonstrado que o FASE mantĂ©m o seu desempenho em redes sob o efeito do churn quando combinado com o algoritmo de monitorização
Structured P2P Technologies for Distributed Command and Control
The utility of Peer-to-Peer (P2P) systems extends far beyond traditional file sharing. This paper provides an overview of how P2P systems are capable of providing robust command and control for Distributed Multi-Agent Systems (DMASs). Specifically, this article presents the evolution of P2P architectures to date by discussing supporting technologies and applicability of each generation of P2P systems. It provides a detailed survey of fundamental design approaches found in modern large-scale P2P systems highlighting design considerations for building and deploying scalable P2P applications. The survey includes unstructured P2P systems, content retrieval systems, communications structured P2P systems, flat structured P2P systems and finally Hierarchical Peer-to-Peer (HP2P) overlays. It concludes with a presentation of design tradeoffs and opportunities for future research into P2P overlay systems
Exploiting Parallelism in the Design of Peer-to-Peer Overlays
Many peer-to-peer overlay operations are inherently parallel and this parallelism can be exploited by using multi-destination multicast routing, resulting in significant message reduction in the underlying network. We propose criteria for assessing when multicast routing can effectively be used, and compare multi-destination multicast and host group multicast using these criteria. We show that the assumptions underlying the Chuang-Sirbu multicast scaling law are valid in large-scale peer-to-peer overlays, and thus Chuang-Sirbu is suitable for estimating the message reduction when replacing unicast overlay messages with multicast messages. Using simulation, we evaluate message savings in two overlay algorithms when multi-destination multicast routing is used in place of unicast messages. We further describe parallelism in a range of overlay algorithms including multi-hop, variable-hop, load-balancing, random walk, and measurement overlay
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