Browsing by Author "Miranda, Hugo"
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- Adaptação ao Contexto em Sistemas de Comunicação HeterogéneosPublication . Mocito, José; Rosa, Liliana; Almeida, Nuno; Miranda, Hugo; Rodrigues, LuísHoje em dia, as aplicações necessitam de ser concebidas para executar numa diversidade de dispositivos heterogéneos, desde servidores, PCs, computadores portáteis, PDAs, ou mesmo telemóveis. No caso de aplicações distribuídas, cada participante poderá estar em execução num dispositivo diferente. Perante esta diversidade, é cada vez mais importante desenhar e concretizar protocolos de comunicação adaptáveis, capazes de se reconfigurar, não só de acordo com o contexto local, mas também em função do contexto dos restantes participantes. Neste artigo é apresentada uma moldura de middleware que facilita o desenvolvimento e execução de protocolos adaptáveis em função do contexto. Esta moldura é ilustrada através de uma aplicação cooperativa, que se executa quer em dispositivos móveis quer fixos, e que beneficia da disponibilidade de uma pilha de comunicação em grupo reconfigurável
- Coerência num sistema transaccional de replicação de objectos em grande-escalaPublication . Martins, João; Almeida, Ricardo; Miranda, Hugo; Rodrigues, LuísObject oriented database systems have become an adequate solution to various problems. In this paper two consistency protocols for large-scale replicated object oriented databases are presented.
- Complete Specification of APIs and Protocols for the MAFTIA MiddlewarePublication . Armstrong, J.; Cachin, C.; Correia, Miguel; Costa, A.; Miranda, Hugo; Neves, Nuno Ferreira; Neves, Nuno M.; Poritz, J. A.; Randell, B.; Lung, Lau Cheuk; Rodrigues, Luís; Stroud, Robert J.; Veríssimo, Paulo; Waidner, M.; Welch, I. S.This document describes the complete specification of the APIs and Protocols for the MAFTIA Middleware. The architecture of the middleware subsystem has been described in a previous document, where the several modules and services were introduced: Activity Services; Communication Services; Network Abstraction; Trusted and Untrusted Components. The purpose of the present document is to make concrete the functionality of the middleware components, by defining their application programming interfaces, and describing the protocols implementing the above-mentioned functionality
- Configuração do Suporte de Comunicação em Ambientes Multi-Utilizador Orientados aos ObjectosPublication . Teixeira, Sandra; Vicente, Pedro; Pinto, Alexandre; Miranda, Hugo; Rodrigues, Luís; Martins, Jorge; Silva, RitoOs sistemas distribuídos interactivos multi-utilizador são aplicações que colocam um complexo conjunto de requisitos sobre o suporte de comunicação subjacente. Um modo de satisfazer cabalmente estes requisitos consiste em utilizar arquitecturas de comunicação configuráveis que suportam a reutilização e composição de componentes. O projecto MOOSCo, "Multi-user Object-Oriented environments with Separation of Concerns" aborda o problema da configuração em sistemas interactivos multi-utilizador. Para suportar a comunicação entre as entidades distribuídas, o projecto recorre ao Appia, uma plataforma de composição de protocolos configurável, que fornece a comunicação em grupo. Este artigo discute o papel do Appia na arquitectura MOOSCo e pretende mostrar como é possível, de uma forma simples e elegante, obter a composição de protocolos mais adequada dependendo dos objectos partilhados pelo ambiente multi-utilizador
- Context Adaptation of the Communication StackPublication . Mocito, José; Rosa, Liliana; Almeida, Nuno; Miranda, Hugo; Rodrigues, Luís; Lopes, AntóniaThis paper presents a middleware framework to support the development of context-aware adaptive communication protocols, that can be reconfigured according not only to the local context, but also to the context of the remaining remote participants. The advantages of the framework are illustrated by using the concrete example of an adaptive group communication protocol. The protocol supports a distributed chat application that can be executed in both fixed PCs and mobile devices
- First Specification of APIs and Protocols for the MAFTIA MiddlewarePublication . Armstrong, J.; Cachin, C.; Correia, Miguel; Costa, A.; Miranda, Hugo; Neves, Nuno Ferreira; Neves, Nuno M.; Poritz, J. A.; Randell, B.; Lung, Lau Cheuk; Rodrigues, Luís; Stroud, Robert J.; Veríssimo, Paulo; Waidner, M.; Welch, I. S.This document describes the first specification of the APIs and Protocols for the MAFTIA Middleware. The architecture of the middleware subsystem has been described in a previous document, where the several modules and services were introduced: Activity Services; Communication Services; Network Abstraction; Trusted and Untrusted Components. The purpose of the present document is to make concrete the functionality of the middleware components, by defining their application programming interfaces, and describing the protocols implementing the above-mentioned functionality
- Gossip-Based Data Distribution in Mobile Ad Hoc NetworksPublication . Miranda, Hugo; Rodrigues, Luís Eduardo TeixeiraWireless networks are useful in many different scenarios. They allow to create emergency networks for catastrophe response, wide area surveillance networks in hostile environments, or simply permit users to share information, play on-line games, and surf the Web. Mobile ad hoc networks are a particular case of wireless networks characterised by the absence of a supporting infrastructure.The thesis addresses the problem of building middleware services that permit to fully exploit the opportunities offered by mobile ad hoc networks. For that purpose, it is required to design algorithms that account for the limitations of mobile devices and that make a careful use of the scarce resources available in ad hoc networks. A central middleware service for mobile applications is data sharing. The thesis addresses the use of data replication as a technique to improve data availability and resource savings in mobile ad hoc networks. In particular, the thesis proposes the use of epidemic protocols to achieve these goals. In this context, the thesis presents the following contributions. It presents and evaluates $\i)$ an algorithm to reduce the number of transmissions required in a broadcast, $\ii)$ an algorithms for the geographical distribution of replicas of data items, and $\iii)$ algorithms to attenuate the impact of node movement in the geographical distribution. Finally, the thesis describes an application of the algorithms to build a concrete application, a version of the Session Initiation Protocol for wireless networks
- A Power-Aware Broadcasting AlgorithmPublication . Miranda, Hugo; Leggio, Simone; Rodrigues, Luís; Raatikainen, KimmoFlooding is an expensive but unavoidable operation in some application scenarios devised for Mobile Ad Hoc Networks (MANETs). In this paper, we present a novel algorithm to reduce the overhead imposed by flooding operations. The algorithm improves previous results by using a distributed function to elect the nodes that will provide the highest additional coverage to previous retransmissions. The algorithm does not require any signalling or imposes special requirements on the participating devices.
- Protocolo Híbrido de Ordem Total Uniforme com entrega OptimistaPublication . Vicente, Pedro; Miranda, Hugo; Rodrigues, LuísBroadcast algorithms with total uniform order simplify the development of applications that use replication as a fault-tolerance technique. This paper presents and compares three alternatives to implement an optimistic delivery service in total order uniform broadcast protocols for large-scale systems.
- Reaching Scalability in Unstructured P2P Networks Using a Divide and Conquer StrategyPublication . Fonseca, Pedro; Miranda, HugoUnstructured 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 is highly inefficient. To improve scalability, unstructured overlays evolved to a two-tiered architecture where regular nodes rely on superpeers to locate resources. 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. In this paper we propose a search algorithm, called FASE, which combines a replication policy and a search space division technique to achieve scalability on unstructured overlays with flat topologies. We present simulation results which validate FASE improved scalability and efficiency