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From chemical signals to event dissemination in a mobile system EPFL

This paper presents the CSC2 algorithm, which leverages the mobility of processes and validity periods of events to enhance dissemination reliability in a mobile ad-hoc network. The algorithm does not rely on multicast or routing algorithms and saves memory by collecting old and noise events. Evaluation results show that CSC2 offers high reliability in a variety of scenarios.

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From chemical signals to event dissemination in a mobile system EPFL

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  1. From chemical signals to event dissemination in a mobile system EPFL Distributed Programming Laboratory Sébastien Baehni, Chirdeep S. Chhabra, Rachid Guerraoui

  2. Motivation Devise an algorithm that implement the topic-based publish/subscribe abstraction in a mobile ad-hoc network environment T2 T2 Topic hierarchy T0 T1 T1 T2 T0 T0

  3. Contribution • The CSC2 (Chemical Signal Communication among Cells) Algorithm • Uses the mobility of the processes and the validity periods of the events to enhance dissemination reliability • Does not rely on any multicast or routing algorithm (one-hop communication) • Saves memory by collecting old and noise events NB: Mobility Friendly Publish/Subscribe, S. Baehni, C. S. Chhabra and R. Guerraoui, EPFL-LPD, Technical Report No 200488.

  4. Cells communicate by exchanging chemical signals The cells only react if they are sensible to these signals The signals have a limited duration and vanish after some time The signals reach only small geographical zones; however, the cells move and hence propagate the “information” Analogy Cell 1 Cell2

  5. Background CSC2 Overview Evaluation Roadmap

  6. Background • Dissemination algorithms • Reliable multicast algorithms • Make assumptions on the stabilization of the network • Use cluster-heads • Switch to flooding • Counter/Distance/Location/Cluster-based • Either use a GPS or are outperformed • Neighboring schemes: • Dominant pruning (two hops neighbors) • The publisher chooses the forwarding nodes • Uses a greedy algorithm • Self pruning (one hop neighbor) • Each node takes the decision to rebroadcast or not • Used in our algorithm (with modifications)

  7. Background • MANET Publish/Subscribe algorithms • Use brokers (Siena, Jedi, …) • Use multicast trees • Disseminate events according to a geographical location (Steam) • Make network stabilization assumptions

  8. Background CSC2 Intuition Evaluation Roadmap

  9. Overview • Three phases: • Neighborhood Detection • Event Dissemination • Garbage Collection Event Dissemination (I) Neighborhood Detection Interests Events Neighbors Interests Events Neighbors T1 e1 p2 T1 e1 p2 Interests Events Neighbors Interests Events Neighbors T1 --- p1 T1 --- p1 <1> <p1,T1> p1 p2 p1 p2 <--> <p2,T1>

  10. Overview Garbage Collection Event Dissemination (II) Interests Events Neighbors Interests Events Neighbors T1   T1 e1 p2 Interests Events Neighbors Interests Events Neighbors T1   T1 e1 p1 <e1, p2> p2 p1 p2 p1

  11. Each process periodically broadcasts heartbeat messages (process identifier and interests) Once a process pi is detected by a process pk, pk puts pi in its neighborhood table if they share common interests If pi and pk do not share any common interest, they simply ignore each other Neighborhood Detection

  12. Two new neighbors exchange their events identifiers according to their common interests Upon the reception of the events identifiers Each process checks if its neighbor misses an event The process sends the events (and the list of its neighbors) to its neighbors after a back-off The back-off is computed according to the number of events to send (the more the events to send, the smaller the back-off) Upon reception of an interested event by pi pi stores the event pi checks if it has to propagate the new event (self pruning) Event Dissemination

  13. Neighborhood collection Each process periodically collects its neighborhood information Event collection The events are collected according to their validity and the number of times they have been propagated Garbage Collection

  14. Background CSC2 Intuition Evaluation Roadmap

  15. Evaluation • Environment • Qualnet simulator (initialized to the default 802.11b values) • Two models • Random Waypoint Model (150 processes, 25km2) • City Section Model (EPFL, 15 processes, 1200x900m2, radio range of 44m) • Speed of the processes and event validity vary for each experiment

  16. Random Waypoint • Reliability according to the speed of the processes, the validity of the event and the interests of the processes (20% versus 80%)

  17. Random Waypoint • Reliability according to the validity of the event and the interests of the processes, in an heterogeneous environment

  18. City Section • Reliability according to the processes interests • Difference of reliability between the processes • Reliability according to the event validity

  19. CSC2 is used to disseminate events in a mobile ad-hoc environment Performance: 90s validity is sufficient to ensure a 95% reliability in the random waypoint model, where 120 processes move at 30mps, in a 25km2 environment The validity and the paths of the processes are extremely important in the City Section Model to let them go through hot points Summary

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