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

2. Minema 2 Devise an algorithm that implement the topic-based publish/subscribe abstraction in a mobile ad-hoc network environment Topic hierarchy T0T0 T1T1 T2T2 T2T2 T2T2 T1T1 T0T0 T0T0 Motivation

3. Minema 3 The CSC 2 (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 Contribution NB: Mobility Friendly Publish/Subscribe, S. Baehni, C. S. Chhabra and R. Guerraoui, EPFL-LPD, Technical Report N o 200488.

4. Minema 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. Minema 5 Roadmap Background CSC 2 –Overview –Evaluation

6. Minema 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. Minema 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. Minema 8 Roadmap Background CSC 2 –Intuition –Evaluation

9. Minema 9 Overview p1p1 p2p2 InterestsEventsNeighbors T1T1 e1e1 p2p2 InterestsEventsNeighbors T1T1 ---p1p1 p1p1 p2p2 InterestsEventsNeighbors T1T1 e1e1 p2p2 InterestsEventsNeighbors T1T1 ---p1p1 Neighborhood Detection Three phases: –Neighborhood Detection –Event Dissemination –Garbage Collection Event Dissemination (I)

10. Minema 10 Overview p1p1 p2p2 InterestsEventsNeighbors T1T1 e1e1 p2p2 InterestsEventsNeighbors T1T1 e1e1 p1p1 p1p1 p2p2 InterestsEventsNeighbors T1T1  InterestsEventsNeighbors T1T1  Event Dissemination (II) Garbage Collection

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

12. Minema 12 Event Dissemination 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 p i –p i stores the event –p i checks if it has to propagate the new event (self pruning)

13. Minema 13 Garbage Collection 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

14. Minema 14 Roadmap Background CSC 2 –Intuition –Evaluation

15. Minema 15 Evaluation Environment –Qualnet simulator (initialized to the default 802.11b values) –Two models Random Waypoint Model (150 processes, 25km 2 ) City Section Model (EPFL, 15 processes, 1200x900m 2, radio range of 44m) –Speed of the processes and event validity vary for each experiment

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

18. Minema 18 Reliability according to the processes interests Difference of reliability between the processes Reliability according to the event validity 20%40%60%80%100% 58%59%63%69%77% 20%40%60%80%100% 41%45%48%54%60% 25s50s75s100s125s150s 11%27%44%52%69%77% City Section

19. Minema 19 CSC 2 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 25km 2 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