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Distributed Token Circulation in Mobile Ad Hoc Networks

Distributed Token Circulation in Mobile Ad Hoc Networks. Navneet Malpani , Intel Corp. Nitin Vaidya , Univ. Illinois Urbana-Champaign Jennifer Welch , Texas A&M Univ . Presented at Int’l Conf. on Network Protocols, Nov 2001 http://faculty.cs.tamu.edu/welch/papers/icnp01.ps or pdf.

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Distributed Token Circulation in Mobile Ad Hoc Networks

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  1. Distributed Token Circulation in Mobile Ad Hoc Networks Navneet Malpani, Intel Corp. Nitin Vaidya, Univ. Illinois Urbana-Champaign Jennifer Welch, Texas A&M Univ. Presented at Int’l Conf. on Network Protocols, Nov 2001 http://faculty.cs.tamu.edu/welch/papers/icnp01.ps or pdf

  2. Introduction • Mobile Ad Hoc Networks (MANETs) • Formed by a collection of wireless mobile hosts, without making use of any existing infrastructure (such as base stations or telephone lines). • Pair of nodes communicate with each other either over a wireless link between the two nodes, or by traversing a sequence of wireless links over several other intermediate nodes.

  3. Example Mobile Ad Hoc Network A B A B C C D E D E

  4. Introduction continued • Usefulness • Disaster recovery • Search and rescue in remote areas • Military operations • Characteristics of Mobile Ad Hoc Networks • Highly dynamic topology • Highly variable message delays • Variable transmission error rates • Constraints on energy consumption • Constraints imposed by wireless interfaces

  5. Token Circulation Definition • Ensure that a token circulates throughout the network, visiting every node infinitely often. • Round: Minimal length sequence of nodes visited to ensure that every node is visited at least once.

  6. Token Circulation Example T T A B A B C E D C A B C E D C A ... T T C Length of round 1: 5 Length of round 2: 6 Length of round 3: 6 D E T T

  7. Token Circulation Application • Total order of message delivery in a group communication service • Key features of a group communication service: • Maintaining information regarding group membership • Communication among nodes in the group in an ordered manner

  8. Token Circulation Application • Token carries a sequence number, which is always incremented. Sender multicasts message with sequence number; receiver delivers in order. OR • Messages are stored in the token itself (large token). • Additional mechanisms are needed to obtain desired level of reliability.

  9. Token Circulation Algorithms • Local Least Recently Visited (LR): forward token to neighbor visited least recently • Local Least Frequently Visited (LF): forward to neighbor visited least frequently A B LR: ACBCDE CACBCDE CACBCD E... C LF: ACBCDE DECACB CDEDEDECACB C... D E

  10. More TC Algorithms Choose next destination among all nodes. • Global Least Recently (GR): forward to any node in network visited least recently • Least Frequently (GF): forward to any node in network visited least frequently

  11. Yet More TC Algorithms • GRN: Global Least Recently + visit intermediate nodes on the path • GFN: Global Least Frequently + visit intermediate nodes on the path (not studied) • Iterative Search: try to find Hamiltonian Path using more history information (see paper for more details)

  12. Performance Measures • Round length: number of nodes visited by the token in a round • Message overhead: number of bytes sent per round • Time overhead: time required to complete a to complete a round

  13. Simulation Results • ns-2 simulator with CMU extensions • System contains 20 nodes initially placed randomly in a 1000m x 300m box • Random Waypoint mobility model • Each algorithm runs as an application on top of TCP and DSR protocol • Results for Static and Dynamic topologies

  14. Static Topologies • Plots of • number of nodes visited • number of bytes sent • amount of time taken during each round, averaged over 50 different scenarios

  15. Discussion of Static Results • LF diverges • GR and GF trivially have best round length, but not so good on messages & time • LR is quite good • Iterative Search is best overall

  16. Dynamic Topologies • Varying speed (6, 12, 18 and 24 m/sec) with constant hello interval of 0.5 sec • Varying hello interval (0.1, 0.3, 0.5 and 0.7 sec) with constant speed of 12 m/sec • Hello Threshold: 3 • Number of scenarios: 30 • Duration of simulation was varied inversely with the speed

  17. Discussion of Dynamic Results • Random Nature of Results • Effect of uncertainty in the topology knowledge due to the hello protocol • Effect of the TCP timeout intervals when partitions occur • Chaotic nature of the algorithms themselves • LR is the best! Close to optimal round length.

  18. Conclusion • Identified new problem for MANETs -- token circulation • Proposed several distributed algorithms • Compared them by simulation • Overall best algorithm : • Iterative Search in the static case • LR algorithm in the dynamic case

  19. Future Work • Identify characteristics of graphs on which LR has good performance -- there are graphs on which it has exponential round length (cf. recent work by Yu Chen) • Integrate token circulation with mechanisms for complete group communication service • Make tolerant of token loss / partitions • Find lower bounds on possible performance and find optimal algorithms

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