On the Accuracy of MANET Simulators

The deployment of wireless applications or protocols in the context of Mobile Ad-hoc NETwork (MANET), often requires to step through a simulation phase. For the results of the simulation to be meaningful, it is important that the model on which is based the simulator matches as closely as possible the reality. In this paper we present the results of the simulation of an algorithm using several popular simulators (OPNET Modeler, NS-2, GloMoSim). The results tend to show that significant divergences exist between the simulators. This can be explained partly by the mismatching of the modelisation of each simulator and also by the different levels of detail provided to implement and configure the simulated scenarios

Consensus with Unknown Participants or Fundamental Self-Organization

We consider the problem of bootstrapping self-organized mobile ad hoc networks (MANET), i.e. reliably determining in a distributed and self- organized manner the services to be offered by each node when neither the identity nor the number of the nodes in the network is initially available. To this means we define a variant of the traditional consensus problem, by relaxing the requirement for the set of participating processes to be known by all at the beginning of the computation. This assumption captures the nature of self-organized networks, where there is no central authority that initializes each process with some context information. We consider asynchronous networks with reliable communication channels and no process crashes and provide necessary and sufficient conditions under which the problem admits a solution. These conditions are routing and mobility independent. Our results are relevant for agreement-related problems in general within self-organized networks

Probabilistic Broadcast for Flooding in Wireless Mobile Ad hoc Networks

Although far from optimal, flooding is an in- dispensable message dissemination technique for network- wide broadcast within mobile ad hoc networks (MANETs). As such, the plain flooding algorithm provokes a high number of unnecessary packet rebroadcasts, causing contention, packet collisions and ultimately wasting precious limited bandwidth. We explore the phase transition phenomenon observed in percolation theory and random graphs as a basis for defining probabilistic flooding algorithms. By considering ideal and realistic models, we acquire a better understanding of the factors that determine phase transition, the consequences of the passage to realistic MANET conditions and to what extent we may benefit from probabilistic flooding in real MANET networks

From a Location Service to a Multicast Service for Wireless Mobile Adhoc Networks

In this paper we propose a novel approach for multicasting in Mobile Ad-hoc Networks (MANETs). Since no fixed infrastructure of servers is assumed in MANETs, efficient location management schemes are necessary in order to store and provide information about various services offered throughout the network. MDLM is the first multicast algorithm relying on a location management service. We thus avoid fragile data structures such as trees or DAGs to manage multicast groups, without reverting to more reliable, yet overhead-prone mesh-based algorithms

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framework for network coding in challenged wireless networ

FRANC: A Lightweight Java Framework for Wireless Multihop Communication

Simulation and emulation are popular means for evaluating wireless Mobile Ad hoc Networks (MANETs) protocols. Since MANETs are highly dependant on their physical environment, these techniques offer only a partial understanding of factors that may influence performance. Deploying real-life MANETs is therefore an indispensable complementary step for the advancement of MANETs. This paper presents FRANC, a dedicated extensible Java framework for the development, deployment and evaluation of applications and algorithms for wireless mobile ad hoc networks

A Location Service Mechanism for Position-Based Multicasting in Wireless Mobile Ad hoc Networks

In this paper we propose a novel location management scheme tailored for multicasting in Mobile Ad-hoc Networks (MANETs). We furthermore propose AMDLM, a location-based multicast algorithm relying on the location management service. Such an approach avoids fragile data structures such as trees or DAGs to manage multicast groups, without reverting to more reliable, yet overhead-prone mesh-based algorithms. AMDLM additionally enables us to derive analytical bounds due to its location-based nature

Cenomanian transgression in the Basque-Cantabrian Basin (northern Spain) and associated faunal replacement

Abstract:The available data concerning the environmental changes and faunal replacements that occurred during the Cenomanian marine transgression in the North of Iberia are integrated and discussed on the basis of new evidence from the invertebrate and vertebrate fossil record. New stratigraphical data and the reassessment of known stratigraphic sections support the correlation of the Cenomanian carbonate-ramp successions from the Iberian margin to the centre of the Basque-Cantabrian Basin during a major transgressive episode. This new stratigraphical framework is the key to understand the changing oceanographic conditions in the area that resulted from a progressive inundation of the Iberian continental platform. This transgression seems to have triggered major faunal replacements in this particular geographic area, starting out around the Albian-Cenomanian transition. Ammonite faunal replacement led to a new radiation of this group that spread out rapidly until their new decline around the Cenomanian-Turonian boundary. A new record of Calycoceras (Newboldiceras) asiaticum spinosum and the first record of a Pachyrhizodontidae indet. (Actinopterygii, Teleostei, Crossognathiformes) from the Iberian Peninsula are reported here from the Cenomanian basal units of the major Late Cretaceous transgressive episode. The two new specimens come from the same level in an outer marine ramp succession near Amurrio, Basque Country, northern Spain, and are representatives of the Cenomanian faunal turnover. The new record of a pachyrhizodontoid fish from the Cretaceous of Iberia is an indication of the ichthyofaunal replacement in this part of the world. The relict fish faunas from the Early Cretaceous of the former island of Iberia were mostly formed by basal neopterygian taxa closely related to those of the marine Jurassic of other parts of Europe. During the Early-Late Cretaceous transition they were replaced by the teleostean-based new stock that constitutes the basis of the Late Cretaceous, Cenozoic, and Recent faunas.Resumen: Se integran y discuten los datos disponibles sobre los cambios ambientales y los reemplazamientos faunísticos que sucedieron en el norte de Iberia durante la transgresión del Cenomaniense, incluyéndose nuevas evidencias de los registros fósiles de invertebrados y vertebrados. Nuevos datos estratigráficos y la revisión de secciones estratigráficas conocidas proporcionan fundamentos para la correlación de las series de rampa carbonatada cenomanienses desde el margen ibérico hasta la zona central de la Cuenca Vasco-Cantábrica, desarrolladas durante un importante episodio transgresivo. Este nuevo esquema estratigráfico configura la base para entender las cambiantes condiciones oceanográficas en la zona de estudio, las cuales resultaron de una progresiva inundación del margen continental ibérico. Esta transgresión se vislumbra como factor determinante para reemplazamientos faunísticos en esta zona, que comenzaron durante el tránsito Albiense-Cenomaniense. Los cambios en las faunas de ammonites condujeron hacia una rápida radiación del grupo hasta un nuevo declive alrededor del tránsito Cenomaniense-Turoniense. Se describen aquí un nuevo registro de Calycoceras (Newboldiceras) asiaticum spinosum y el primer registro de Pachyrhizodontidae indet. (Actinopterigii, Teleostei, Crossognathiformes) de la Península Ibérica, provenientes de la parte basaldel episodio transgresivo cenomaniense. Ambos son representativos del cambio faunístico y proceden del mismo nivel estratigráfico en una serie de rampa carbonatada externa cerca de Amurrio, País Vasco, España. Asimismo, este primer Pachyrhizodontoidei del Cretácico de Iberia indica un cambio importante en las faunas de teleósteos en esta parte del mundo. Las faunas relictas de peces del Cretácico inferior de la entonces isla de Iberia estaban básicamente compuestas por neopterigios basales directamente relacionados con los del Jurásico marino de otras partes de Europa. Durante la transición Cretácico Inferior-Cretácico Superior fueron paulatinamente reemplazados por nuevos grupos de teleósteos, los cuales constituyen la mayor parte de las formas del Cretácico Superior, del Cenozoico y actuales

Solving Agreement Problems with Weak Ordering Oracles

Agreement problems, such as consensus, atomic broadcast, and group membership, are central to the implementation of fault-tolerant distributed systems. Despite the diversity of algorithms that have been proposed for solving agreement problems in the past years, almost all solutions are crash detection based (CDB). We say that an algorithm is CDB if it uses some information about the status crashed/not crashed of processes. Randomized consensus algorithms are rare exceptions non-CDB algorithms. In this paper, we revisit the issue of non-CDB algorithms. Instead of randomization, we consider ordering oracles. Ordering oracles have a theoretical interest (e.g., they extend the state of the art of non-CDB algorithms) as well as a practical interest (e.g., they remove altogether the burden involved in tuning timeout mechanisms). To illustrate their use, we present solutions to consensus and atomic broadcast, and evaluate the performance of the atomic broadcast algorithm in a cluster of workstations