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ExOR : Opportunistic Multi-Hop Routing for Wireless Networks

ExOR : Opportunistic Multi-Hop Routing for Wireless Networks. By. Sanji Biswas and Robert Morris M.I.T. Computer Science Artifical Intelligence Laboratory. Overview. Problem: Route selection in wireless network Traditional routing: Single path routing New routing: Multi-path routing

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ExOR : Opportunistic Multi-Hop Routing for Wireless Networks

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  1. ExOR: Opportunistic Multi-Hop Routing for Wireless Networks By. Sanji Biswas and Robert Morris M.I.T. Computer Science Artifical Intelligence Laboratory

  2. Overview • Problem: • Route selection in wireless network • Traditional routing: • Single path routing • New routing: • Multi-path routing • Goal: • Maximize network throughput

  3. What is ExOR ? • ExOR: Extremely Opportunistic Routing • Integrated Routing and MAC protocol • Unicast transfers in multi-hop wireless networks • Multiple opportunities to make progress • Transmit in Batch

  4. ExOR – Basic Concept. • Utilization of intermediate nodes in packets forwarding D S Entirety

  5. Advantage of ExOR • Maximize Channel Usage • Reduce re-transmission (buffer packets at nodes) • ACK-free mechanism (ACK implicit) • Increase throughput • Cooperative diversity (with single forwarder) • Use long radio links with high loss rates • Take advantage of transmission that reach unexpectedly far or fall unexpectedly short

  6. Traditional vs. ExOR routing Traditional: src-B-D-dst ExOR: many

  7. ExOR - BASIC IDEA. • Agreement on who is in sub-set via messages • Source broadcasts batch • Sub-set nodes receive and store packet • Sub-set node closest to destination broadcasts packet first

  8. ExOR routing process 3 1 4 D S 2 Batch Forwarder List

  9. ExOR routing process 3 1 4 D S 2 Forwarder List The highest priority forwarder broadcasts the packets in its buffer Destination received the packets and node #1 also inform other nodes by broadcasting

  10. ExOR routing process 3 1 4 D S 2 Forwarder List The next node in the priority list/forwarder list broadcast the packets that not received by the higher priority nodes(obtained from higher node’s batch map). The node #2 inform lower priority nodes by his copy of batch map

  11. ExOR routing process 3 1 4 D S 2 Forwarder List Next node repeat the same process

  12. ExOR routing process 3 1 4 D S 2 Forwarder List

  13. ExOR routing process Destination broadcasts 10 copies of his batch map 3 1 4 D S 2 Forwarder List The source broadcasts packets that higher nodes haven’t received

  14. ExOR routing process 3 1 4 D S 2 Forwarder List Every node update its own batch map by receiving destination’s batch map

  15. ExOR routing process The whole process repeats until destination receive 90% packet of the batch 3 1 4 D S 2 Forwarder List Every node update its own batch map by receiving destination’s batch map

  16. Packets transmission division. Per batch 90% 10% 1st ExOR REST Traditional Routing

  17. ExOR - DESIGN CHALLENGES • Low Overhead on Agreement Protocol • Disagreement and Duplicate is low • The node “Closest” to destination forwards packet first • Select most useful nodes • Avoid simultaneous transmissions

  18. “Closeness” Estimated transmission count (ETX) to node E from each node Side: ExOR uses only the forward delivery probability

  19. Scheduling transmission. • Purpose: • avoid collision, ACK-free • Marginal links – carrier sense • Set timer to schedule transmission Timer = current timer + estimate time (remaining packets)

  20. ExOR - Node State • Packet Buffer : stores received packets • Local Forwarder : prioritized forwarder list • Forwarding Timer : time to start forwarding • Transmission Tracker: rate of sender and packets left to send • Batch Map (Check List): highest-priority node to have received copy of a packet

  21. ExOR - PACKET HEADER FORMAT • BatchID : The batch packet belongs to • PktNum : Current packet’s offset in batch • BatchSz : Number of packets in batch • FragNum : Current packet's offset within the fragment • FragSz : Size of the currently sending node's fragment (in packets) • FwdListSize : Number of forwarders in the list • ForwarderNum : Current sender's offset within the list • Forwarder List : Copy of the sender's local forwarder list • Batch Map : Copy of the sending node's batch map

  22. Simulation Environment • Performed on Roofnet (out-door roof top, 802.11b) • 38 nodes • 6 square kilometers distributed area • PC with 802.11b card with omni-directional atenna

  23. ExOR Transfer Example.

  24. ExOR vs. Traditional Routing 25 highest throughput pairs Increase throughput by prevent unnecessary retransmissions

  25. ExOR vs. Traditional Routing 25 lowest throughput pairs • Increase throughput by takes advantage of the choice of forwarders

  26. Transmission based on ETX The number of transmissions made by each node during a 1000-packet transfer from N5 to N24.

  27. Future works.: • Multi-rates ExOR • Multi-channel ExOR (Cooperative diversity) • TCP modifications – ATCP? • Error-correction/Bit-error recovery • UDP

  28. Q&A • You have question? We have answer!

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