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Routing in a Delay Tolerant Network

Routing in a Delay Tolerant Network. Sushant Jain (UW), Rabin Patra (UCB), Kevin Fall (Intel Research Berkeley) and Gaetano Borriello (UW). Outline. Background Delay Tolerant Networking Example Routing challenges Routing algorithms Knowledge oracles Cost based approach

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Routing in a Delay Tolerant Network

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  1. Routing in aDelay Tolerant Network Sushant Jain (UW), Rabin Patra (UCB), Kevin Fall (Intel Research Berkeley) and Gaetano Borriello (UW)

  2. Outline • Background • Delay Tolerant Networking Example • Routing challenges • Routing algorithms • Knowledge oracles • Cost based approach • Current status and Future Work

  3. Connecting a remote village Low latency, Low bandwidth (4Kbps). • High delay, • High bandwidth • Low latency, Low bandwidth (4Kbps). Night only

  4. DTN routing challenges • Instantaneous end to end path may not exist • Large queuing delays • Buffer limitations at intermediate nodes • Large messages • Traditional e2e routing approach will not work • Mail protocol will not work • How to route in such networks ? • Focus: Dynamics of topology are known

  5. Other DTN networks • Mobile networks • Example: Military adhoc network • Disconnectivity due to node mobility • Sensor networks • Large environment monitoring infrastructure • Disconnectivity due to scheduled power outages • Deep Space Networks • Large RTTs (order of minutes)

  6. The routing problem • Nodes with finite storage capacity • Links with dynamic behavior • Time varying capacity (c(t)) • C(t) = 0, if link is down • Message • Src, Dst, start-time, size • Output: Compute path(s) for every message • Objective: Minimize delay • Other objectives: message delivery ratio, minimize $$ cost

  7. Knowledge Oracles • Contacts Oracle • Complete link schedule (c(t)) • Time dependent information • Contacts summary Oracle: • Frequency of satellite availability • Time independent information • Queuing Oracle: Link queues, available storage • Two versions: Local vs Global • Traffic Demand Oracle

  8. Oracle use vs Performance centralized LP distributed Contacts + Global Queuing + Traffic Demand EDAQ EDLQ Contacts + Global Queuing “Performance” Contacts + Local Queuing ED MED Contacts Contacts Summary Oracles used

  9. Earliest delivery algorithm (ED) • Define link costs and find minimum cost path • Cost varies with time • Cost of link at time $T$ = time till the link appears next • Example: Time for the bus to appear next • Compute minimum cost paths over this dynamic cost assignment • Modified Dijkstra by taking into account time of arrival • Optimal under low congestion

  10. Summary of findings • Dynamic algorithms outperform static techniques • Difference increases with network disconnectivity • ED optimal under low congestion • Very bad performance under congestion • Need to incorporate queuing information • Local queuing performance comparable to global queuing performance

  11. Future work • Imperfect knowledge • Sensitivity to correctness of oracles • Routing when contacts are opportunistic • Epidemic routing • Use of replication • Implementation in the DTN framework

  12. Thank You Q & A More information at: http://www.cs.washington.edu/homes/sushjain/dtn

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