On the Cost/Delay Tradeoff of Wireless Delay Tolerant Geographic Routing

1. On the Cost/Delay Tradeoff of Wireless Delay Tolerant Geographic Routing Argyrios Tasiopoulos MSc, student, AUEB Master Thesis presentation

2. Introduction • Many networks are characterized by: • Intermittent Connectivity. • Long or variable delays. • In both cases traditional TCP/IP protocols fail. • Delay Tolerant Networking addresses these issues. 4 to 20 minutes Master Thesis presentation

3. Delay Tolerant Networks (DTNs) • In Delay-Tolerant Networks each node can hold packets indefinitely in a persistent buffer. • The previous problems are addressed by store-and-forward message switching.

4. Mobile Delay Tolerant Networks • In mobile DTNs, nodes can carry a packet physically in their buffer. • Therefore, we actually have store-carry-and-forward packet switching. Master Thesis presentation

5. DTNs Protocol Design • In DTNs we have an extra degree of freedom regarding the delay in data delivery. • We can trade off delay in order to improve other metrics. • Our case of study concerning the improvement of aggregate transmission cost. • We care about the behavior of aggregate transmission cost of a packets given a delivery delay. WoWMoM San Francisco 2012

6. Aggregate Transmission Cost • What we mean in this work when we talk about aggregate transmission cost? • The cost of interference (typically proportional to transmission area), and/or • the energy consumption of a transmission (typically fixed). Master Thesis presentation

7. Coming next • Part A: Optimal Cost/Delay Tradeoff Formulation • Part B: Cost/Delay Tradeoffs in Geographic Routing • Part C: Simulation Environments and Results Master Thesis presentation

8. Part A: Optimal Cost/Delay Tradeoff Formulation. Master Thesis presentation

9. Optimal Cost/Delay Tradeoff • We take the typical approach of evolving graphs (Ferreira 2004). • We divide the time into discrete time intervals, called epochs. • We make the assumptions that during each epoch: • the network topology remains fixed, hence creates a network replica for the specific epoch, and • all packet transmissions can take place. Master Thesis presentation

10. Cost/Delay Evolving Graph • We define as Cost/Delay Evolving Graph (C/DEG) the graph comprised by: • consecutive replicas, • link arcs, which connect nodes along the same replica, and • storage arcs, which connect the same nodes along consecutive replicas. Master Thesis presentation

11. Punctual vs. Optimal Cost/Delay Curve • Given a packet source we can execute any one-to-many shortest path algorithm. • We define the Punctual Cost/Delay Curve (PC/DC), as the minimum-cost journey of exactlyt epochs, between two nodes. • We define the Optimal Cost/Delay Curve (OC/DC), as the minimum-cost journey of all journeys with the maximum duration oft epochs. WoWMoM San Francisco 2012

12. Punctual Cost/Delay Curve Example WoWMoM San Francisco 2012

13. Punctual vs. Optimal Cost/Delay Curve Example Master Thesis presentation

14. Part B: Cost/Delay Tradeoffs in Geographic Routing. Master Thesis presentation

15. Geographic routing • In geographic routing a source sends a message to the geographic location of the destination. R Master Thesis presentation

16. Geographic routing • Then, the packet route from source to destination is calculated “on the fly”. Complete network topology Master Thesis presentation

17. Protocol family • Each node which executes a protocol of this family: • Applies a Neighbor Evaluation Rule (NER) to its immediate neighbor nodes, which returns the best of them. • Calculates the minimum-cost path to the best neighbor. • Forwards the packet to the next hop node along the minimum-cost path. Master Thesis presentation

18. Protocol Family Example Calculate shortest-cost path Forward the packet to the next hop node Execute NER Find the best Master Thesis presentation

19. Protocol Family Variations • Next we define 5 member of this protocol family. • All rules differ on NER. • For the rest of this presentation: • node A is the packet holder which performs the NER, • node B is a candidate neighbor of A, and • node D the packet destination. Master Thesis presentation

20. Motion Vector (MoVe)(LeBrun et al.,2005) • MoVe NER: Select as best the node with the current or future closest distance from the destination. Minimizes |ZD| Master Thesis presentation

21. AeroRP (Peters et al., 2011) • AeroRP NER: Selects as best the node with the biggest relative velocity towards destination Maximizes vRB Master Thesis presentation

22. Minimum Cost-per-Progress (MCpPR) • MCpPR NER minimizes the ratio: Master Thesis presentation

23. Balance Ratio Rule (BRR) • Our first novel protocol minimizes the ratio: • We define αas theconversion coefficient. • Which strikes a balanced between cost and delay by trying to keep them both low. Master Thesis presentation

24. Composite Rule (CR) • MCpPR rule tries to maximize the immediate transmission gains. • BRR tries to maximize the benefits of the physical transportation of store-carry-and-forward packet switching. • Hence, we define Composite Rule (CR) as the best of two worlds which minimizes simultaneously the ratios of MCpPR and BRR : Master Thesis presentation

25. Achievable Cost/Delay Curve (AC/DC) • We define the AC/DC as the curve that give for each epoch, the minimum aggregate transmission cost that a protocol can achieve for a pair of nodes. • If the protocol has tunable parameters concerning the tradeoff, an achievable cost/delay curve (AC/DC) is calculated in a similar way to OC/DC, over the complete range of results of these parameters. Master Thesis presentation

26. Achievable Cost/Delay Tradeoff Example Master Thesis presentation

27. Part C: Simulation Environments and Results. Master Thesis presentation

28. Performance Evaluation Settings • We evaluate our protocols in the 3 following settings: • empty space setting, • home region setting, and • urban setting. Master Thesis presentation

29. Simulation parameters • The common tunable parameter for all these protocols is the restricted radius R’ which determines the maximum transmission hop length. • CR and BRR have the extra tunable parameter α. • Standard case: The nodes move with random velocities and we have a quadratic aggregate transmission cost function (equal to d2where d the transmission distance). Master Thesis presentation

30. Empty Space Setting Master Thesis presentation

31. Empty Space Setting – Fixed velocities and cost function Master Thesis presentation

32. Home Region Setting Master Thesis presentation

33. Urban Setting Master Thesis presentation

34. Urban Setting-Fixed velocities Master Thesis presentation

35. Conclusions • Our immediate contributions: • The formulation of optimal tradeoff between the packet delivery delay and the aggregate transmission cost existing in all DTNs. • The study of this tradeoff in the context of geographic routing • Our two novel rules with results close to the optimal. • Our most important contribution: • We set the agenda for a systematic evaluation of cost/delay tradeoffs in a variety of DTNs settings. Master Thesis presentation

36. Thank you