Distributed Token Circulation in Mobile Ad Hoc Networks

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

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

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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.

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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
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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

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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.

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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
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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

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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)

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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

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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

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Static Topologies

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

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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

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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

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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.

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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

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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