1. National Taiwan University Department of Computer Science and Information Engineering Vinod Namboodiri and Lixin Gao University of Massachusetts Amherst IEEE Transactions on Vehicular Technology, July 2007 speaker: Yu-Hsun Chen Prediction-Based Routing for Vehicular Ad Hoc Networks

2. National Taiwan University Department of Computer Science and Information Engineering 2 Outline  Introduction  Related Work  Highway Mobility Model  PBR Protocol  Experiments and Results  Conclusion

3. National Taiwan University Department of Computer Science and Information Engineering 3 Introduction 1  Connectivity while on the road will be an important application area Gaming and multimedia streaming Safety application Low cost on safety products  Considerations to achieve connectivity while on the road Bandwidth Cost seamless mobility

4. National Taiwan University Department of Computer Science and Information Engineering 4 Introduction 2  Wireless technology for Internet access 3G, 4G, WiMax, satellite-based  seamless connectivity  More expansive Wireless LAN  Low-cost  High bandwidth  Capability of ad hoc mode  Limited range

5. National Taiwan University Department of Computer Science and Information Engineering 5 Introduction 3  Wireless connectivity from a vehicle Inter-vehicular communications (IVCs) Internet connectivity  Static gateways alongside roads: [3][4] Deployment cost Route switching between gateways  Mobility gateway approach Low cost Without geopolitical boundaries Fewer gateway switches

6. National Taiwan University Department of Computer Science and Information Engineering 6 Introduction 4 WWAN WLAN mobile gateway

7. National Taiwan University Department of Computer Science and Information Engineering 7 Introduction 5  Contributions Mobility model  Highway mobility patterns Prediction-based routing protocol  Predict how long routes will last  Preemptively creates new routes to replace old ones before they break

8. National Taiwan University Department of Computer Science and Information Engineering 8 Outline  Introduction  Related Work  Highway Mobility Model  PBR Protocol  Experiments and Results  Conclusion

9. National Taiwan University Department of Computer Science and Information Engineering 9 Mobile Ad hoc Routing  Proactive All nodes send routing messages at predetermined periods Difficulty: what messaging period is best to maximize routing performance  Reactive On-demand basis Lack sensitivity toward new better routes  Location-based Rely on a location server Overhead to maintain vehicles’ current information

10. National Taiwan University Department of Computer Science and Information Engineering 10 VANET Routing Classification J. Bernsen and D. Manivannan, “ Unicast routing protocols for vehicular ad hoc networks: A critical comparison and classification ”, Pervasive and Mobile Computing, 2009

11. National Taiwan University Department of Computer Science and Information Engineering 11 Outline  Introduction  Related Work  Highway Mobility Model  PBR Protocol  Experiments and Results  Conclusion

12. National Taiwan University Department of Computer Science and Information Engineering 12 Highway Mobility Model 1  Assumption: all vehicles are within certain speed bounds  Discrete time model Car speed:

13. National Taiwan University Department of Computer Science and Information Engineering 13 Highway Mobility Model 2

14. National Taiwan University Department of Computer Science and Information Engineering 14 Outline  Introduction  Related Work  Highway Mobility Model  PBR Protocol  Experiments and Results  Conclusion

15. National Taiwan University Department of Computer Science and Information Engineering 15 Prediction-Based Routing Protocol  Obtaining location and velocity information of vehicles on the route to the gateway  Prediction algorithm uses this information to predict when the route will break

16. National Taiwan University Department of Computer Science and Information Engineering 16 Basic Operation 1  When a node needs to communicate to a Internet location Broadcast an RREQ  TTL, sequence number, source ID, destination ID, source node’s direction, a list of nodes and their directions  A neighbor receiving the RREQ forwards it if 1. TTL > 1 and higher sequence number 2. TTL > 1, the same sequence number as previous packet, and all intermediate nodes traveling in the same direction

17. National Taiwan University Department of Computer Science and Information Engineering 17 Basic Operation 2  When the RREQ reaches a gateway with the desired route to the sought destination The gateway send back an RREP using the chain of nodes in the RREQ  When multiple gateways reply 1. choose the gateway with minimum hops and all nodes on the route are moving in the same direction as itself 2. choose the gateway with minimum hops  When multiple route from the same gateway Choose the route that has the maximum predicted route lifetime

18. National Taiwan University Department of Computer Science and Information Engineering 18 Basic Operation 3  The RREP in conjunction with the prediction algorithm is used to give the source a predicted lifetime for the route  The source sends out a new RREQ just before this timer expires The preemption interval is adaptive based on the lifetime of the route  If the last packet was sent before a certain time threshold pred-timeout Turn off the preemptive route creation procedure

19. National Taiwan University Department of Computer Science and Information Engineering 19 Obtaining Route Lifetime  Information in the RREP Location and velocity information Set a lifetime field in the RREP  Gateway: lifetime ← maxlifetime  Intermediate node: predict the life time using the prediction algorithm  If the lifetime value is smaller than the lifetime mentioned in the RREP packet Replace the lifetime field in the RREP

20. National Taiwan University Department of Computer Science and Information Engineering 20 Prediction Algorithm 1    

21. National Taiwan University Department of Computer Science and Information Engineering 21 Prediction Algorithm 2 The lifetime for the route ACDE is 10s

22. National Taiwan University Department of Computer Science and Information Engineering 22 “Moving Closer” Condition bonus

23. National Taiwan University Department of Computer Science and Information Engineering 23 Link on Oncoming Traffic

24. National Taiwan University Department of Computer Science and Information Engineering 24 PBR Variants  PBR A new route is constructed to the nearest gateway  PBR-S Stick with a gateway as much as possible to avoid gateway switching  PBR-M Select the gateway among all those within a certain number of hops with the largest predicted route lifetime

25. National Taiwan University Department of Computer Science and Information Engineering 25 Outline  Introduction  Related Work  Highway Mobility Model  PBR Protocol  Experiments and Results  Conclusion

26. National Taiwan University Department of Computer Science and Information Engineering 26 Routing Metrics and Simulation Environment  Routing Metrics Packet delivery ratio Route failures (percentage of dropped packets) Number of RREQs

27. National Taiwan University Department of Computer Science and Information Engineering 27 Effect of Vehicle and Gateway Density on Connectivity

28. National Taiwan University Department of Computer Science and Information Engineering 28 Effect of Node and Gateway Density on Routing Performance * The number of gateways fix at 10

29. National Taiwan University Department of Computer Science and Information Engineering 29 Effect of Node and Gateway Density on Routing Performance * The number of nodes fix at 50

30. National Taiwan University Department of Computer Science and Information Engineering 30 Effect of Mobility Pattern on Routing Performance * {# of nodes, # of gateways}

31. National Taiwan University Department of Computer Science and Information Engineering 31 Comparing PBR with Reactive and Proactive Protocols * 10 gateways; 40 nodes

32. National Taiwan University Department of Computer Science and Information Engineering 32 Minimizing Gateway Switching * 10 gateways

33. National Taiwan University Department of Computer Science and Information Engineering 33 Conclusion  The predictable motion of vehicles could be exploited to predict route failures  A PBR protocol is presented Reduction in route failure Higher packet delivery ratio Keeping control overhead in check