Détection des événements de congestion de TCP

Ces dernières années ont vu un intérêt croissant pour l'étude de la mesure des flots TCP. Plusieurs méthodes ont été proposées afin d'estimer de façon précise et rapide le taux de perte des paquets. Toutefois, et à notre meilleure connaissance, l'estimation et l'identification des événements de congestion TCP ne sont actuellement pas adressées. Suite à la standardisation de TFRC (TCP Friendly Rate Control), nous assistons à un intérêt croissant pour les protocoles de transport utilisant un contrôle de congestion de type rate-based. Aussi, ce type de contrôle de congestion repose sur la même base métrologique que celle de TCP. Dans ce contexte, la détermination précise des événements de congestion (CE) est un élément clé. En effet, ces derniers donnent une information essentielle pour le calcul d'un débit d'émission qui soit équivalent à celui de TCP dans les mêmes conditions. L'objet de cet article est de mieux identifier les CE de TCP afin de fournir une référence précise à ces nouveaux protocoles. Nous vérifions dans cette étude que TCP n'identifie pas de manière efficace les CE du réseau et proposons une méthode capable de mieux les déterminer. Cette détection est effectuée passivement à partir de la capture temps réel des paquets d'un flot TCP

Transport congestion events detection (TCED): towards decorrelating congestion detection from TCP

TCP (Transmission Control Protocol) uses a loss-based algorithm to estimate whether the network is congested or not. The main difficulty for this algorithm is to distinguish spurious from real network congestion events. Other research studies have proposed to enhance the reliability of this congestion estimation by modifying the internal TCP algorithm. In this paper, we propose an original congestion event algorithm implemented independently of the TCP source code. Basically, we propose a modular architecture to implement a congestion event detection algorithm to cope with the increasing complexity of the TCP code and we use it to understand why some spurious congestion events might not be detected in some complex cases. We show that our proposal is able to increase the reliability of TCP NewReno congestion detection algorithm that might help to the design of detection criterion independent of the TCP code. We find out that solutions based only on RTT (Round-Trip Time) estimation are not accurate enough to cover all existing cases. Furthermore, we evaluate our algorithm with and without network reordering where other inaccuracies, not previously identified, occur

Win-win opportunities combining high yields with high multi-taxa biodiversity in tropical agroforestry

Resolving ecological-economic trade-offs between biodiversity and yields is a key challenge when addressing the biodiversity crisis in tropical agricultural landscapes. Here, we focused on the relation between seven different taxa (trees, herbaceous plants, birds, amphibians, reptiles, butterflies, and ants) and yields in vanilla agroforests in Madagascar. Agroforests established in forests supported overall 23% fewer species and 47% fewer endemic species than old-growth forests, and 14% fewer endemic species than forest fragments. In contrast, agroforests established on fallows had overall 12% more species and 38% more endemic species than fallows. While yields increased with vanilla vine density and length, non-yield related variables largely determined biodiversity. Nonetheless, trade-offs existed between yields and butterflies as well as reptiles. Vanilla yields were generally unrelated to richness of trees, herbaceous plants, birds, amphibians, reptiles, and ants, opening up possibilities for conservation outside of protected areas and restoring degraded land to benefit farmers and biodiversity alike

Seaside Risk Detection from Mesh Connected Consumer Devices

International audienceno abstrac

Contrôle de trafic pour service privilégié sur réseaux sans fil

Conçus à l'origine comme une extension des réseaux locaux maires, les réseaux locauxsans fil ont ouvert la voie à de nouveaux usages liés à l'ubiquité. Les caractéristiques ducanal radio ainsi que la mobilité des terminaux compliquent la problématique de la qualitéde service (QoS : Quaîity of Service] de ces nouveaux réseaux. Cette thèse s'intéresseau support de la différenciation de service sur les réseaux IEEE 802.11 ad hoc. Elle commence par l'étude du support de la différenciation de service sur un réseau monosaut. Le principe consiste à contrôler la demande au niveau IP sur la base de Tétât du réseau. Deux moyens de mise en œuvre sont étudiés : détermination de l'état du réseau par échangede signalisation et estimation de l'état du réseau par mesure locale. Ensuite, une solution au problème de l'inéquité d'accès sur réseau ad hoc est proposée. En effet, sur certaines configurations, l'accès au canal ne dépend plus uniquement de la charge mais aussi de la localisation relative des nœuds et la resynchronisation des instants de démarrage de la procédured'accès de 802.11 DGF. Enfin, pour simplifier le contrôle des ressources et réduire lesinterférences co-canaux, une organisation hiérarchique du réseau est proposée. A cettefin, nous proposons une modélisation pour la localisation des cellules et un algorithme de répartition des fréquences aux cellules.Designed as an extention to wired local area networks, wireless local area networks lead to new potentials such as ubiquity. Wireless channels characteristics as well as mobility of terminais complexify thé support of Quaîity of Service in thèse networks. This disser tation concentrâtes on thé support of service differentiation in IEEE 802.11-based ad hoc networks. It begins wifch thé study of thé support of service differentiation in a single hop network. The idea consists in controlling thé traffic at thé IP level according to thé net work state. Two types of implementation are studied: computation of thé network state by means of message exchange and estimation of thé network state by local measurements. Then, a solution to channel acccss unfairness issues is proposed. Indeed, under certain con figurations, channel access does not dépend solely on thé traffic load but also on thé relative position of thé nodes. The proposed solution consists in thé propagation of thé receiving state of nodes and in thé synchronization of thé beginning of 802.11 access opération. Fi-nally, in ordcr to simphfy resources management and to reduce co-channel interférences, a hierarchical organization of thé network is proposed. It is based on a topology control or clustcring sclieme and a, channel assignaient mechanism.SAINT DENIS/REUNION-Droit Lettre (974112101) / SudocSudocFranceReunionFRR

Equité pour réseau ad hoc Wi-fi

National audienceLa norme IEEE 802.11 est devenue un standard de la technologie sans fil. Cependant, son utilisation dans les réseaux ad hoc pose des problèmes de performance et en particulier, en terme d’équité d’accès. Cet article présente une méthode d’accès équitable (FWM : Fair Wireless MAC) qui est une extension de l’applicabilité de la méthode d’accès de 802.11 aux réseaux ad hoc. Pour cela, un mécanisme de type tonalité d’occupation est couplé à la détection de la porteuse afin de synchroniser les états des noeuds adjacents à une communication. En étendant la connaissance du voisinage des noeuds, la résolution des contentions de 802.11 peut de nouveau s’appliquer efficacement. L’inéquité due à la transmission sans fil est également traitée par FWM. La solution proposée est tirée de l’analyse des causes d’inéquité de 802.11 dans un réseau ad hoc. FWM sera comparé aux solutions de type tonalité d’occupation. L’appréciation de la solution proposée est faite avec le simulateur NS-2 sur des situations présentant des phénomènes d’inéquité

Enhancing Disaster Management by Taking Advantage of General Public Mobile Devices: Trends and Possible Scenarios

International audienceWhen a crisis occurs, particular infrastructures that are specific to the emergency situation are deployed in order to support rescue operations. Indeed, the normally used ones may have suffered from the disaster resulting in an altered service or may not be available at all. This process concerns physical (logistics) as well as immaterial (information) items delivery. Nowadays, a special emphasize has been put on the latter as it has been proven ([CAM 12], [TAN 09] and [LEF 14]) that it is a major requirement to ensure that the former is realized properly and more generally to address the crisis. Generally, required information aims at answering to the following basic questions: What (happened)? When (did it happened)? Where (is the disaster located)? And possibly How (can it be reached)? That is why research and development works have been led to create technologies that can manage information acquisition and delivery in harsh environments: specific communication networks, rugged equipment, solar-powered devices, etc. Those means are dedicated to risk and emergency experts who are specially trained to evolve under difficult circumstances and the tools they rely on are designed to cope with this context

Using general public connected devices for disasters victims location

International audienceInformation Technologies (IT) have largely contributed to improve disaster management by providing new means to acquire, process and broadcast information to the various actors. However, most of the work was targeted toward the risk experts: decision makers, rescue teams, firemen, etc. Nowadays, a new parallel trend seems to emerge: it consists in taking into account signal from consumer devices like cell phones (basic ones to smartphones), tablets, computers or other devices but light networks equipment (routers, WiFi access points) too. More particularly, our goal is to rely on the wave activity generated by those equipments, which are generally personal, to detect where victims are more likely to be located after a disaster, typically a seism. To reach this aim, we present the feasibility of mixing two approaches to acquire data by measuring their radio activity

Hierarchical Area-Based Address Autoconfiguration Protocol for Self-organized Networks

International audienceNode autoconfiguration is one of the main issues in self-organized networks. One class of approaches relies on hierarchical organization of nodes. This kind of structuration aims to deal with scalability issues, especially for wireless networks. But building and maintaining a hierarchy is generally expensive for these resource-limited networks. We propose a low-cost distributed, hierarchical, location-based address au-toconfiguration protocol. Each node infers its address from those of its one-hop neighbors and from its relative position to them. In this way we obtain a globally-consistent organization resulting from local interactions only. This reduces the latency and the overhead generated during address configuration. Moreover this scheme is the first step towards the design of a scalable routing protocol taking advantages of the proposed hierarchical addressing