4 research outputs found
A Markov chain model for drop ratio on one-packet buffers DTNs
Most of the efforts to characterize DTN routing are focused on the trade-off between delivery ratio and delay. Buffer occupancy is usually not considered a problem and most of the related work assumes infinite buffers. In the present work, we focus on the drop ratio for message forwarding considering finite buffers. We model message drops with a continuous time Markov chain (CTMC). To the best of our knowledge, there is no previous work with such approach. We focus on the worst case with 1-packet buffers for message forwarding in homogeneous inter-contact times (ICT) and 2-class heterogeneous ICT. Our main contribution is to link the encounter rate(s) with the drop ratio. We show that the modeled drop ratio fits simulation results obtained with synthetic traces for both cases
Modelling the delay distribution of Binary Spray and Wait routing protocol
This article proposes a stochastic model to obtain the end-to-end delay law
between two nodes of a Delay Tolerant Network (DTN). We focus on the commonly
used Binary Spray and Wait (BSW) routing protocol and propose a model that can
be applied to homogeneous or heterogeneous networks (i.e. when the
inter-contact law parameter takes one or several values). To the best of our
knowledge, this is the first model allowing to estimate the delay distribution
of Binary Spray and Wait DTN protocol in heterogeneous networks. We first
detail the model and propose a set of simulations to validate the theoretical
results.Comment: Accepted for publication. AOC 201
Satellites d'observation et réseaux de capteurs autonomes au service de l'environnement
La collecte dâinformations et leur transmission au travers dâun rĂ©seau de communications peut ĂȘtre effectuĂ©e par des rĂ©seaux de capteurs autonomes ainsi que par des satellites dâobservation. Lâutilisation conjointe de ces rĂ©seaux fournirait des donnĂ©es complĂ©mentaires et permettrait Ă lâHumanitĂ© de pĂ©renniser son avenir en comprenant les mĂ©canismes du monde qui lâentoure. Ces derniĂšres annĂ©es, le secteur spatial a montrĂ© une volontĂ© dâunifier et de faciliter la rĂ©utilisation des dĂ©veloppements rĂ©alisĂ©s avec la crĂ©ation de filiĂšres de plateformes multi-missions ainsi que la dĂ©finition de protocoles applicables Ă diffĂ©rents contextes. Lâobjectif de cette thĂšse est dâĂ©tudier les caractĂ©ristiques des diffĂ©rentes technologies dâobservation afin dâen exploiter les points communs. Ă ces fins, nous nous intĂ©ressons aux technologies et aux architectures utilisĂ©es dans de tels contextes. Nous proposons alors une architecture de rĂ©seau rĂ©pondant aux contraintes des systĂšmes les plus communĂ©ment utilisĂ©s dans un tel cadre. Les principales contraintes des scĂ©narios dâobservation sont liĂ©es Ă la forte intermittence des liens et donc au manque de connexitĂ© du rĂ©seau. Nous nous orientons donc vers une solution ayant recours au concept de rĂ©seaux tolĂ©rants au dĂ©lai. Dans un tel contexte, lâexistence dâune route entre la source et la destination nâest pas garantie. Câest pourquoi les protocoles de communication utilisĂ©s propagent gĂ©nĂ©ralement plusieurs exemplaires dâun mĂȘme message vers plusieurs entitĂ©s afin dâaugmenter le taux de dĂ©livrance. Nous avons souhaitĂ© diminuer lâutilisation des ressources du rĂ©seau tout en conservant des performances similaires afin dâaugmenter lâefficacitĂ© du rĂ©seau. AprĂšs avoir proposĂ© une architecture commune, nous nous sommes focalisĂ©s sur les spĂ©cificitĂ©s des diffĂ©rents segments de notre rĂ©seau afin de rĂ©pondre localement Ă ces problĂšmes. Pour le segment satellite, nous nous sommes plus spĂ©cialement concentrĂ©s sur les techniques de gestion de mĂ©moire. Nous considĂ©rons un satellite dĂ©filant avec une mĂ©moire embarquĂ©e limitĂ©e, collectant des donnĂ©es en provenance de passerelles. Il sâagit alors de sĂ©lectionner les messages les plus urgents quitte Ă dĂ©poser sur une autre passerelle les messages moins contraints. Sur le rĂ©seau de capteurs terrestre, nous nous sommes focalisĂ©s sur la diminution de lâutilisation des ressources du rĂ©seau. Pour cela nous avons utilisĂ© lâhistorique des rencontres entre les nĆuds et analysĂ© lâinfluence de la quantitĂ© de mĂ©moire allouĂ©e aux accusĂ©s de rĂ©ception sur les performances du rĂ©seau. Nous sommes parvenus Ă atteindre des performances supĂ©rieures aux solutions existantes Ă moindre frais. Les solutions proposĂ©es peuvent ĂȘtre mises en Ćuvre et appliquĂ©es dans diffĂ©rents contextes applicatifs. ABSTRACT : Data gathering and transmission through a communicating network can be obtained thanks to wireless sensor networks and observation satellites. Using both these technologies will allow mankind to build a sustainable future by understanding the world around. In recent years, space actors have demonstrated a will to reuse the developed technologies by creating multiple programs platforms and defining context-agnostic protocols. The goal of this thesis is to study the characteristics of several observation technologies to exploit their similarities. We analyse the existing technologies and architectures in several contexts. Then, we propose a networking architecture handling constraints of most commonly used systems in such a context. The main constraints of observation scenarios are due to the links intermittence and lack of network connectivity. We focus on a solution using the delay tolerant networking concept. In such a context, a path between source and destination might not exist at all time. That is why most proposed protocols send multiple copies of a message to increase the delivery ratio. We wanted to decrease network resource use while keeping a similar performance to increase network efficiency. After having proposed a common architecture, we focused on particularities of each network segment to solve problems locally. Concerning the satellite part, we focused specifically on memory management techniques. We considered a low earth orbit satellite with a limited on-board buffer, gathering data from gateways. The goal is then to select the most urgent messages even though the least urgent ones are sent back to the ground. On the terrestrial sensor network part, we focused on the decrease of network resource use. We used the history of encounters between nodes and analysed the influence of the proportion of memory allocated to acknowledgements on network performance. We achieved better performance than existing solutions and at lower cost. The proposed solutions can be deployed and applied in several applications