A Hybrid Routing Approach for Opportunistic Networks

1
A Hybrid Routing Approach for Opportunistic
Networks

• Ling-Jyh Chen1, Chen-Hung Yu2, Tony Sun3,
• Yung-Chih Chen1, and Hao-hua Chu2
• 1 Academia Sinica
• 2 National Taiwan University
• 3 University of California at Los Angeles

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Opportunistic Networks

• A type of DTN
• Intermittent Links
• Very Large Delays
• High Link Error Rates
• Network contacts appear arbitrarily w/o prior
  information neither scheduled optimal routing
  nor mobile ferry based approaches can be applied.

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Opportunistic Networks

• Potential Applications
• interconnect mobile search and rescue nodes in
  disaster areas
• allow message exchanges in developing areas
• permit scientific monitoring of wilderness
• Examples
• ZebraNet, DieselNet, CenWits, UWSN,

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Our Contribution

• We proposed an effective data forwarding scheme
  for opportunistic networks, called H-EC.
• H-EC combines the strength of erasure coding and
  the advantages of aggressive forwarding.
• We showed that H-EC performs aggressively for
  very small delay performance cases and remain
  robust for worst-case delay performance cases.

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Outline

• Background and Overview
• Related Work
• Erasure coding
• H-EC details
• Evaluation
• Summary and Future Work

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Related Work

• Data forwarding schemes for opportunistic
  networks
• Flooding based
• Epidemic routing (Vahdat 00)
• Controlled flooding (Harras 05)
• Coding based
• Erasure coding based data forwarding (Wang 05,
  Liao 06)
• Network coding based data forwarding (Widmer 05)
• Prediction based schemes
• Probabilistic routing (Lindgren 04)
• Mobility pattern based forwarding (Leguay 05)

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Erasure Coding

• Provide better fault-tolerance by adding
  redundancy without the overhead of strict
  replication (e.g., Reed-Solomon, Gallager,
  Tornado, and IRA codes)
• Applications P2P, overlay routing, WSN, data
  storage, etc.
• Our work is based on the generic erasure coding
  concept.

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Erasure Coding
(r,n)(2,4)
A
B
C
D
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Previous Approaches

• direct contact (DC)
• simple replication (srep) (k2)
• EC erasure coding based data forwarding (r2,
  n4)

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Proposed Approach (I)

• A-EC erasure coding aggressive forwarding
  
  (r2, n4)
• Issues Black-holes
• unreliable (limited battery power and/or buffer
  size)
• hardly moving closer towards the destination

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Proposed Approach (II)

• H-EC Hybrid of EC and A-EC
• First copy is sent using EC
• Second copy is sent using A-EC during the
  residual contact duration after sending the first
  EC block
• Algorithms for scheduling the 2nd copy of EC
  blocks SF, FI, and BI

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Simulation

• DTNSIM a java based simulator
• Implementation
• EC erasure coding based data forwarding
• R-EC EC simple replication
• A-EC erasure coding aggressive forwarding
• H-EC EC A-EC
• Scenarios
• 34 nodes (including source and destination)
• two-hop scenario
• 1200 bytes/msg, 12 msg/day, 160 days
• Contact time Inter-contact time power-law w/
  coefficient 0.6
• EC block size 150 bytes, r 2, n 16
• Black-holes buffer size 2 msg

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Results I General scenario
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Results II Black-hole scenario
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Overhead Analysis

• r replication factor of erasure coding
• n the number of relays among which erasure code
  blocks are split
• k the replication factor of srep algorithm
• Strategies to reduce overhead
• Explicit ACK (or passive cure)
• Adaptive Coding
• Probabilistic Forwarding

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Summary

• An effective data forwarding scheme is essential
  for opportunistic networks.
• H-EC combines the strength of erasure coding and
  the advantages of aggressive forwarding.
• H-EC is effective and robust, even when
  black-holes are present.

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Future Work

• H-EC Evaluation
• Using realistic mobility traces
• Analytical model
• H-EC Adaptation
• Redundancy level
• Probabilistic forwarding
• H-EC Applications
• Scalable data transfer
• Testbed

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Thank You!

• For more information
• http//nrl.iis.sinica.edu.tw/
  http//nrl.iis.sinica.edu.tw/DTN/