1. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Ahmad Al Hanbali, Richard Boucherie, Jan-Kees van Ommeren and Roland de Haan

2. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Mobile ad hoc networks (i) Static and mobile hosts (e.g., laptops, cellular phones, PDAs) Wireless communications No infrastructure, self-organizing

3. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Application (i) Wild-life monitoring –Wild species equipped with radios form mobile ad-hoc network –Monitoring system for interactions of individuals and groups

4. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Application (ii) Vehicular networks –Vehicles and road signs/structures form mobile ad-hoc network –E.g., distribution of traffic information, internet access in cars

5. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Application (iii) Disaster relief networks –Existing communication means may fail –Rescue workers and equipment form an ad hoc network to smoothen the rescue operation by allowing for voice/data- communication

6. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Mobile ad hoc networks (ii) Main (functional) characteristics: –Wireless communication (dynamic channel conditions, interference, collisions) –Intermittent connectivity due to mobility (routing is an issue) –Distributed network control (no central entity)

7. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Research questions Transfer delays and buffer levels in such networks (QoS guarantees) (Optimal) routing protocols Network design (include extra stations?)

8. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Related literature Experimental studies (mobility process) Simulations Analytical models (infinite populations, single packet)

9. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Our contribution Practice: –Analytical modelling framework for mobile ad hoc networks Theory: –Extension of the literature on polling systems

10. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Research method Original situation: Modelling: create analytical queueing model containing key characteristic: Intermittent connectivity due to mobility

11. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Queueing model Key ingredients: –(Random) Arrival process of customers –Service requirements –Single server Simplest model: M/M/1 queue Performance measures: –Queue length –Sojourn time

12. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Intermittent connectivity Assumption: –mobile stations move in local neighborhood Modelling: –discrete set of locations for each station –stations remain a random time at a location –given the specific locations of the stations, data transmissions may occur

13. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Toy example - model Network: 1 fixed source S, and 1 mobile destination D Depending on the location of destination D, there exists either a link (state {0}) between S and D (i.e., S can transmit data to D) or no link (state {1}) SD ? 0 1

14. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Toy example - analysis Let packets generated at S correspond to customer arrivals; Let a link correspond to a server being available in a queueing model; Link: No link: => Specific queueing model: Unreliable-server model [Gaver, 1962] SD ?

15. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Towards more general networks: a polling system Single-server multi-queue model Key characteristics: –Multiple queues –Random arrival of customers –Service requirements –Server “visits” queues in some order –Service discipline Performance measures: –queue-length distribution and delay measures

16. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Polling system - refined Specific details to study MANETs: –Autonomous service discipline Random visit times of server (~ exponential time-limited discipline) –Probabilistic routing of the server –Customer routing –Preemptive service (acc. to preemptive-repeat-random policy)

17. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Solution approach (i) Construct relations for p.g.f.’s of queue-length distribution at specific instants, viz.: –Server arrival instants to Q i and server departure instants from Q i: –Server departure instants from Q i and server arrival instants to Q j QiQi QjQj aiai bibi t ajaj bjbj QiQi QjQj bibi t ajaj bjbj akak

18. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Solution approach (ii): System of equations (in terms of p.g.f.’s) Numerical iterative solution method: Joint queue-length distribution

19. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Applications of polling systems (i) Queue-length and delay measures for, e.g.,: –Multi-hop tandem networks, –General single-channel networks (IEEE 802.11): SRD ?? S T V ? ? U ? ? ? ?

20. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Applications of polling systems (ii) Optimization: –Optimal delay via power control by adjusting visit time parameter, –Optimal delay via channel time assignment by adjusting visit time parameter S T V ? ? U ? ? ? ? SRD ?? ?

21. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Results Modelling framework for evaluation of emerging communication paradigms (Delay-Tolerant Networking, opportunistic networking) Exact analysis of polling systems operating under a novel service discipline

22. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Concluding remarks Numerical solution approach creates need for (mean value) approximations Extend framework to: –Multi-server polling models –More general server visit times

23. PhD-TW-Colloquium, October 09, 2008Polling systems as performance models for mobile ad hoc networking Thanks for your attention