Publications

Multicast is an important building block for many applications in MANETs, including data dissemination, service discovery, publish-subscribe, among others. Therefore, it has been widely studied and many solutions can be found in the literature. However, most existing multicast protocols are tailored to a specific type of mobility pattern and therefore are unable to excel in face of heterogeneous topology stability conditions. This paper proposes and evaluates TSAMP, a Topology Stability-Aware Multicast Protocol for MANETs that exploits locally perceived mobility conditions in order to promote the use of stable routes, when available.

This paper addresses the problem of multipath routing in hybrid wireless mesh networks. We study the use of clustering algorithms to facilitate the discovery and deployment of non-interfering multipath routes in these settings. In this context we propose a novel combination of clustering and routing techniques aiming at minimizing interferences between transmissions of neighbouring nodes. We provide a comparative evaluation results and show that our solution offers an interesting tradeoff between the signalling cost, the time required to set up and maintain paths, and the properties of the discovered paths.

Neste artigo propomos um novo algoritmo de monitorizacao para redes em malha sem fios, baseado em clusters adaptativos. Os nos organizam-se automaticamente numa malha de clusters semi-circulares e a informacao de monitorizacao de cada cluster e agregada pelos lideres dos clusters e posteriormente reencaminhada para a estacao de monitorizacao. O algoritmo tem em conta a existencia de fluxos de dados na rede, e tenta minimizar a interferencia do trafego de monitorizacao nesses fluxos.

Este artigo aborda o problema do encaminhamento multi-rota em redes sem fios em malha. Neste contexto, propomos um algoritmo de clustering que facilita a escolha de multiplas rotas que nao interfiram mutuamente ao nivel radio, assim como um algoritmo que combina facetas pro-activas e reactivas para determinar e manter estas rotas. O protocolo resultante e avaliado atraves de simulacoes no NS-2, mostrando que a nossa solucao obtem um equilibrio interessante entre o custo de sinalizacao necessario para descobrir as rotas e a eficacia das rotas encontradas.

Flooding is a fundamental building block in multi-hop networks (both mobile and static); for instance, many routing protocols for wireless ad hoc networks use flooding as part of their route discovery/maintenance procedures. Unfortunately, most algorithms have configuration parameters that must be tuned according to the execution environment, in order to provide the best possible performance. Given that ad hoc environments are inherently unpredictable, dynamic, and often heterogeneous, anticipating the most adequate configuration of these algorithms is a challenging task. This paper presents @Flood, an adaptive protocol for flooding in wireless ad hoc networks that allows each node to auto-tune the configuration parameters, or even change the forwarding algorithm, according to the properties of the execution environment. Using @Flood, nodes auto-configure themselves, circumventing the need for pre-configuring all the devices in the network for the expected operational conditions, which is impractical or even impossible in very dynamic environments.

In recent years the world has witnessed many catastrophic events where the intervention of first responders was required to manage massive disaster scenarios. To be effective, emergency management teams must be able to coordinate and communicate efficiently. To the best of our knowledge no solution has been proposed to support the communication and coordination of these teams in an integrated fashion. In this paper we propose MUSTUS, an architecture that provides communication mechanisms and coordination primitives, based on the interaction through a tuple space, whose semantics are specifically designed to support the needs of emergency management applications.

A difusao em grupo e util para suportar diferentes aplicacoes em MANETs, incluindo a disseminacao de dados, descoberta de servicos, publicacao-subscricao, entre outras. Consequentemente, este problema tem sido extensivamente estudado. No entanto, a maior parte dos protocolos de difusao sao desenhados para um padrao especifico de mobilidade e, consequentemente, sao incapazes de atingir um bom desempenho perante condicoes de mobilidade heterogenea. Este artigo propoe e avalia o HAMP, um protocolo de difusao para MANETs que combina a eficiencia de abordagens estruturadas e a robustez de esquemas baseadas em inundacao, adaptando o seu algoritmo de encaminhamento de acordo com as condicoes de mobilidade observadas localmente em cada no.

Establishing content-based publish/subscribe in the resource constrained and failure prone environment of Mobile Ad-Hoc Networks (MANETs) is a highly challenging task. Movement of nodes and network partitioning can require frequent and possibly expensive reorganizations of the publish/subscribe system. Many approaches towards publish/subscribe in MANETs either rely explicitly on location information, or are characterized by a high subscription and publication overhead. In this paper we present preliminary research on how geographical distribution of subscriptions may help to overcome some shortcomings of both approaches.

This paper proposes a probabilistic publish-subscribe approach for Mobile Ad Hoc Networks (MANETs). In our approach publishing and subscribing are implemented using random walks in the network. This strategy avoids the cost of continuously maintaining complex routing structures that are unstable due to node mobility. While previous research on gossip based publish-subscribe for MANETS assumed the collaboration of all nodes in the network our solution operates on an overlay constructed on top of DSR, allowing for only a small fraction of the nodes to participate in the publish-subscribe system.

Total order broadcast protocols have been successfully applied as the basis for the construction of many fault-tolerant distributed systems. Unfortunately, the implementation of such a primitive can be expensive both in terms of communication steps and of number of messages exchanged. To alleviate this problem, optimistic total order protocols have been proposed. This paper addresses the problem of offering optimistic total order in geographically wide-area systems. We present a protocol that outperforms previous work, by minimizing the average latency of the optimistic notification.

Total order broadcast protocols are a fundamental building block in the construction of many fault-tolerant distributed applications. Unfortunately, total order is an intrinsically expensive operation. Moreover, there are certain algorithms that perform better in specific scenarios and given network properties. This paper proposes and evaluates an adaptive protocol that is able to dynamically switch between different total order algorithms. The protocol allows to achieve the best possible performance, by selecting, in each moment, the algorithm that is most appropriate to the present network conditions. Experimental results show that, using our protocol, adaptation can be achieved with negligible interference with the data flow.

Today's applications are developed to support all sorts of devices and networking solutions. For instance, in distributed applications each participant may be executing in a different type of device, with its specific resource potentialities and constraints. With this diversity in mind it is increasingly more important to design and implement adaptive communication protocols, that can be reconfigured in regard to, not only the local context, but also as a function of the context of the remaining participants. This paper presents an architecture that makes use of a reconfigurable communication stack to offer support for group communication in hybrid networks, where participants may execute in wired networks, MANETs, or both simultaneously.

This paper presents a middleware framework to support the development of context-aware adaptive communication protocols stacks. The protocol stacks can be reconfigured according not only to the local context, but also to the context of the remaining remote participants. The context information and the current node configuration feed a Markov decision process that is used to derive the appropriate reconfigurations. The advantages of the framework are illustrated using the concrete example of an adaptive group communication protocol. An experimental validation has been performed using a distributed chat application that can be executed in both fixed PCs and mobile devices.

A total order protocol is a fundamental building block in the construction of distributed fault-tolerant applications. Unfortunately, the implementation of such a primitive can be expensive both in terms of communication steps and of number of messages exchanged. This problem is exacerbated in large-scale systems, where the performance of the algorithm may be limited by the presence of high-latency links. Optimistic total order protocols have been proposed to alleviate this problem. However, different optimistic protocols offer quite distinct services. This paper makes an overview of different optimistic approaches and shows how they can be combined in a single adaptive protocol.

This 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.

Hoje em dia, as aplicacoes necessitam de ser concebidas para executar numa diversidade de dispositivos heterogeneos, desde servidores, PCs, computadores portateis, PDAs, ou mesmo telemóveis. No caso de aplicacoes distribuidas, cada participante podera estar em execucao num dispositivo diferente. Perante esta diversidade, e cada vez mais importante desenhar e concretizar protocolos de comunicacao adaptaveis, capazes de se reconfigurar, nao so de acordo com o contexto local, mas tambem em funcao do contexto dos restantes participantes. Neste artigo e apresentada uma moldura de middleware que facilita o desenvolvimento e execucao de protocolos adaptaveis em funcao do contexto. Esta moldura e ilustrada atraves de uma aplicacao cooperativa, que se executa quer em dispositivos moveis quer fixos, e que beneficia da disponibilidade de uma pilha de comunicacao em grupo reconfiguravel.