HYMAD: Hybrid DTN-MANET Routing for Dense and Highly Dynamic Wireless Networks

In this paper we propose HYMAD, a Hybrid DTN-MANET routing protocol which uses DTN between disjoint groups of nodes while using MANET routing within these groups. HYMAD is fully decentralized and only makes use of topological information exchanges between the nodes. We evaluate the scheme in simulation by replaying real life traces which exhibit this highly dynamic connectivity. The results show that HYMAD outperforms the multi-copy Spray-and-Wait DTN routing protocol it extends, both in terms of delivery ratio and delay, for any number of message copies. Our conclusion is that such a Hybrid DTN-MANET approach offers a promising venue for the delivery of elastic data in mobile ad-hoc networks as it retains the resilience of a pure DTN protocol while significantly improving performance.Comment: 7 pages, 6 figure

Decays of the Littlest Higgs Z_H and the Onset of Strong Dynamics

The Little Higgs mechanism, as realized in various models, requires a set of new massive gauge bosons, some of which mix with gauge bosons of the Standard Model. For a range of mixing angles the coupling of gauge bosons to scalars can become strong, ultimately resulting in a breakdown of perturbative calculation. This phenomenon is studied in the Littlest Higgs model, where the approach to strong dynamics is characterized by increasing tree-level decay widths of the neutral Z_H boson to lighter gauge bosons plus multiple scalars. These increasing widths suggest a distinctive qualitative collider signature for the approach to the strong coupling regime of large Higgs and other scalar multiplicities. In this work we catalog the kinematically allowed three-body decays of the Z_H, and calculate the partial width of the process Z_H to Z_L H H. This partial width is found to be larger than the comparable two-body decay Z_H to Z_L H for values of the SU(2) mixing angle cosine(theta) less than 0.13, indicating divergence of the littlest Higgs sigma field expansion at values of cosine(theta) larger than a simple parametric calculation would suggest. Additionally, we present analytical expressions for all two-body decays of the Littlest Higgs Z_H gauge boson, including the effects of all final-state masses

Plausible Mobility: Inferring Movement from Contacts

We address the difficult question of inferring plausible node mobility based only on information from wireless contact traces. Working with mobility information allows richer protocol simulations, particularly in dense networks, but requires complex set-ups to measure, whereas contact information is easier to measure but only allows for simplistic simulation models. In a contact trace a lot of node movement information is irretrievably lost so the original positions and velocities are in general out of reach. We propose a fast heuristic algorithm, inspired by dynamic force-based graph drawing, capable of inferring a plausible movement from any contact trace, and evaluate it on both synthetic and real-life contact traces. Our results reveal that (i) the quality of the inferred mobility is directly linked to the precision of the measured contact trace, and (ii) the simple addition of appropriate anticipation forces between nodes leads to an accurate inferred mobility.Comment: 8 pages, 8 figures, 1 tabl

Relieving the Wireless Infrastructure: When Opportunistic Networks Meet Guaranteed Delays

Major wireless operators are nowadays facing network capacity issues in striving to meet the growing demands of mobile users. At the same time, 3G-enabled devices increasingly benefit from ad hoc radio connectivity (e.g., Wi-Fi). In this context of hybrid connectivity, we propose Push-and-track, a content dissemination framework that harnesses ad hoc communication opportunities to minimize the load on the wireless infrastructure while guaranteeing tight delivery delays. It achieves this through a control loop that collects user-sent acknowledgements to determine if new copies need to be reinjected into the network through the 3G interface. Push-and-Track includes multiple strategies to determine how many copies of the content should be injected, when, and to whom. The short delay-tolerance of common content, such as news or road traffic updates, make them suitable for such a system. Based on a realistic large-scale vehicular dataset from the city of Bologna composed of more than 10,000 vehicles, we demonstrate that Push-and-Track consistently meets its delivery objectives while reducing the use of the 3G network by over 90%.Comment: Accepted at IEEE WoWMoM 2011 conferenc

Performance of Opportunistic Epidemic Routing on Edge-Markovian Dynamic Graphs

Connectivity patterns in intermittently-connected mobile networks (ICMN) can be modeled as edge-Markovian dynamic graphs. We propose a new model for epidemic propagation on such graphs and calculate a closed-form expression that links the best achievable delivery ratio to common ICMN parameters such as message size, maximum tolerated delay, and link lifetime. These theoretical results are compared to those obtained by replaying a real-life contact trace.Comment: 5 pages, 4 figures. Accepted for publication in IEEE Transactions on Communication

Modèle de propagation opportuniste pour soulager l'infrastructure 3G

International audienceNous étudions la diffusion massive de contenus en déplaçant une partie du trafic du réseau d'infrastructure 3G vers un réseau opportuniste sans pour autant sacrifier la fiabilité. Dans ce papier, nous étudions un modèle de propagation de messages dans un réseau opportuniste afin de pouvoir prédire l'évolution de la prochaine propagation et calculer le nombre optimal de copies à injecter dans le réseau au début d'une diffusion

Graphes d'accessibilité dynamiques

International audienceLes graphes dynamiques sont de plus en plus utilisés dans de nombreux contextes et servent notamment à modéliser les réseaux opportunistes. Nous formalisons ici la notion de graphe d'accessibilité dynamique qui permet simplement de rendre compte des possibilités d'envoi de messages dans des réseaux avec une durée de traversée d'arête et un délai maximal de remise fixé. Ce formalisme nous permet de proposer un algorithme efficace de calcul des graphes d'accessibilité dynamiques que nous validons sur deux jeux de données rééls