Message Ferrying Approach for Data Delivery in Sparse Mobile Ad Hoc Networks

1. Wenrui Zhao, Mostafa Ammar, and Ellen Zegura (2004) Presented by Justin Yackoski CISC861 Message Ferrying Approach for Data Delivery in Sparse Mobile Ad Hoc Networks

2. The Problem – Sparse Networks • High chance of network not being fully connected at all times, but we want to be able to communicate to everyone all the time.

3. Previous Solution – Epidemic Routing • When one node encounters another node, give that node a copy of all stored data

4. Previous Solution – Epidemic Routing • Since this is a mobile network, assume nodes from one partition will eventually move close enough to another partition to communicate with it

5. Previous Solution – Epidemic Routing • The mobile node then “infects” the other partition with the data it knows about, so that the data is effectively transmitted across the gap.

6. Problems with Epidemic Routing • Any ideas on problems with this?

7. Problems with Epidemic Routing • Will nodes ever actually move between partitions?

8. Problems with Epidemic Routing • How long will it take until nodes move?

9. Problems with Epidemic Routing • Buffering/transmitting – we must know about all our partition's data that needs to be sent to another partition, and if we want to send data to another partition, we have to tell the as many other nodes as we can so they can try to send it. • Lots of duplicate effort

10. Solution – Message Ferrying • Some nodes (“message ferries”)recruited/designed specifically to move between partitions

11. Solution – Message Ferrying • Introduce non-randomness into movement of nodes, exploit mobility of nodes to help deliver data.

12. Why Ferry instead of fixing network? • Crisis – battlefield/disaster, existing connectivity destroyed, must find temporary solution • Geography – very sparse network, impossible to keep connected, or mountains, water, etc. make certain areas very sparse • Cost – Use existing mobile entities (buses as in DakNet) to reduce cost • Service – Provide privacy / alternate route in untrusted environment.

13. Message Ferrying Assumptions(in this paper) • Location awareness of all nodes (GPS, etc.) • Single ferry • Ferry has unlimited buffer space to store messages & unlimited energy to move around • Ferry is invincible

14. Node-Initiated MF (NIMF) • Ferry moves through entire network on a well-known route. • Nodes pro-actively move toward ferry route when they want to send data to another node • Ferry sends out “Hello” beacons, nodes reply with an “echo” message, and then messages are exchanged. Node passes responsibility of delivering messages onto ferry.

15. Node-Initiated MF (NIMF)

16. NIMF – Message Drops • Nodes have fixed buffers, so may drop messages if their buffer overflows • All messages have timeouts set on them, and will be removed from node or ferry buffer when they timeout

17. NIMF – Trajectory Control • We want to minimize message drops and delay • Nodes must both move to ferry and perform their normal nodely duties • Define the Work Time Percentage (WTP) - a node must be free to work on its assigned tasks most of the time

18. NIMF – Trajectory Control • Nodes only go to ferry if: • They can fulfill their WTP requirement and go to the ferry • The cost associated with possible message drops is greater than a certain threshold

19. Ferry-Initiated Message Ferrying (FIMF) • NIMF uses some of the node's time and resources in movement to/from ferry, which we'd like to avoid. • Assuming ferry moves faster than nodes, the ferry can move to the nodes instead • Also assume nodes have a long-range radio to send service requests to the ferry if it is somewhat nearby

20. Ferry-Initiated Message Ferrying (FIMF) • When a node sends a service request to the ferry, enters “associated” mode, and periodically gives ferry updated location

21. FIMF

22. FIMF

23. FIMF – Notification Control • Minimize message drops while conserving use of energy in long-range service request messages • As in NIMF, nodes only send service requests when cost of not sending one (and possibly dropping messages) exceeds a certain threshold • Only send request when ferry is less than a certain distance away • Notification Message Rate (NMR) – max frequency long-range messages can be sent at

24. FIMF – Trajectory Control • Since ferry has unlimited resources, only cost in visiting a node is the latency caused by the time needed to go to and from the node. • Minimize total latency of visiting all nodes with pending service requests • NP-hard, so must use heuristics • Must estimate costs because nodes move

25. FIMF – Trajectory Control Heuristics • Nearest Neighbor (NN) – Go to closest node to current position with a service request, then to closest node from that position, etc. Minimize total latency of going to the nodes • Traffic-Aware (TA) – Consider both location and message drop information, try to minimize expected message drops (roughly minimizing total latency because more latency = more timeouts) • NN & TA equally good in experiments

26. Experiment Setup • Use 802.11 DCF with 250m range for short-range, simplified model for long-range • Don't count ferry energy consumption • Both constant bit rate and burst traffic

27. Effect of Node Buffer Size on Delivery Rate

28. Effect of Node Buffer Size on Delivery Rate • Epidemic routing needs much larger buffer to have similar message delivery rate because of buffer contention in storing other nodes' messages

29. Effect of Node Buffer Size on Message Delay

30. Effect of Node Buffer Size on Message Delay • Delay in epidemic routing is lower because MF explicitly delays going to ferry if there is plenty of room in the buffer • Also need to consider that MF delivers 2X as many messages as epidemic, so some messages do get through faster, others don't make it at all

31. Effect of Node Buffer Size on Energy Efficiency • =

32. Effect of Node Buffer Size on Energy Efficiency • MF only needs 2 hops (source to ferry, ferry to receiver) to deliver message • MF avoids flooding • With larger buffer, FIMF can broadcast long-range service request less frequently • NIMF not affected, however cost of physically moving to ferry is not considered

33. Effect of Node Mobility on Energy Efficiency

34. Effect of Node Mobility on Energy Efficiency • Epidemic routing works better with increased mobility, because more nodes are infected with a message faster, increasing its delivery rate & reducing delay • FIMF is not affected because the ferry pro actively moves to nodes • NIMF is only affected by node speed, since nodes are the ones moving to the ferry

35. Effect of WTP on NIMF Performance

36. Effect of WTP on NIMF Performance

37. Effect of WTP on NIMF Performance

38. Effect of WTP on NIMF Performance • Increase in WTP causes decrease in delivery rate because nodes are allowed to visit ferry less often • Increase in WTP does not affect message delay because messages are already queued as long as buffer allows • Increase in WTP lowers energy efficiency because energy is wasted on messages that end up timing out in the ferry

39. Effect of NMR on FIMF Performance

40. Effect of NMR on FIMF Performance

41. Effect of NMR on FIMF Performance

42. Effect of NMR on FIMF Performance • Increase in NMR only affects delivery rate if timeout is small • Increase in NMR does not change message delay because message transmissions already delayed as long as possible • Increase in NMR increases energy efficiency because more messages are batched up before a service request is sent out

43. Effect of Transmission Range on FIMF Performance

44. Effect of Transmission Range on FIMF Performance

45. Effect of Transmission Range on FIMF Performance

46. Effect of Transmission Range on FIMF Performance • Increase in range increases delivery rate because ferry route is shorter, so less timeouts on ferry • Increase in range does not affect message delay due to batching done by nodes • Increase in range causes some increase in energy efficiency to the extent it reduces drops. For large range, node energy is wasted because ferry is not moving as much

47. Conclusions • MF is better than epidemic routing at providing a high delivery rate and a high energy efficiency. Message delay is higher, but could be lowered as needed if energy efficiency relaxed.

48. Future Work • Multiple ferries – ferries need to cooperate and determine who will service which requests, areas, etc. Ferries could also exchange messages with eachother • Node coordination – nodes could forward other nodes' messages a short number of hops, a “gateway” node could inform neighbors of ferry's presence and allow relaying of messages to ferry

49. Future Work • Long-Range Communication – There are situations where using long-rage communication to directly deliver message between nodes is better (i.e., faster) than using the ferry depending on the application.

50. The Questions • Give a situation/constraint where either NIMF or FIMF is superior over the other & briefly explain why • How could the ferry and destination contact each other to finish delivery of messages in NIMF or FIMF? Paper is not explicit on this