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MAC Reliable Broadcast in Ad Hoc Networks Ken Tang, Mario Gerla

MAC Reliable Broadcast in Ad Hoc Networks Ken Tang, Mario Gerla University of California, Los Angeles (ktang, gerla@cs.ucla.edu). Overview. Ad hoc network introduction Medium access control (MAC) protocol Broadcast limitation Broadcast Medium Window (BMW) protocol

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MAC Reliable Broadcast in Ad Hoc Networks Ken Tang, Mario Gerla

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  1. MAC Reliable Broadcast in Ad Hoc Networks Ken Tang, Mario Gerla University of California, Los Angeles (ktang, gerla@cs.ucla.edu)

  2. Overview • Ad hoc network introduction • Medium access control (MAC) protocol • Broadcast limitation • Broadcast Medium Window (BMW) protocol • The broadcast medium window • Example • Simulation results • Conclusion

  3. Base Base Base Instant infrastructure, multi-hop wireless ad hoc networks Ad Hoc Network Introduction Standard base station cellular networks

  4. Overview • Ad hoc network introduction • Medium access control (MAC) protocol • Broadcast limitation • Broadcast Medium Window (BMW) protocol • The broadcast medium window • Example • Simulation results • Conclusion

  5. An Example of Random Access Scheme (IEEE 802.11) – Unicast Mode 2 6 1 0 4 5 RTS CTS 3 DATA Steps: ACK A. Collision avoidance Remote B. Node 0 transmits RTS to node 4 C. Node 4 transmits CTS and node 6 attempts an RTS D. Node 0 transmits DATA E. Node 4 transmits ACK

  6. MAC Broadcast Limitation • Reliable unicast • RTS/CTS to acquire the channel • ACK to make sure data is received • What about broadcast? • Send data and pray!

  7. An Example of Random Access Scheme (IEEE 802.11) – Broadcast Mode 2 6 1 0 4 5 3 DATA Steps: A. Collision avoidance B. Node 0 transmits DATA

  8. Overview • Ad hoc network introduction • Medium access control (MAC) protocol • Broadcast limitation • Broadcast Medium Window (BMW) protocol • The broadcast medium window • Example • Simulation results • Conclusion

  9. Broadcast Medium Window (BMW) • Ad hoc multicast routing protocols rely on MAC broadcast to achieve multicasting • Typical ad hoc MAC layer protocols (e.g., IEEE 802.11) are very “lossy” in the broadcast mode • We propose a novel scheme, Broadcast Medium Window (BMW) to provide robust (but not 100% reliable) MAC broadcasting

  10. The Broadcast Medium Window • Conventional window protocol (e.g., TCP) transmits packets in sequence to a single destination • The “broadcast window” protocol transmits packets by increasing sequence numbers to ALL neighbors • The window protocol “visits” each neighbor in Round Robin order to retransmit packets which the node missed in the broadcast transmission

  11. seqno = 1 seqno = 0 - 1 seqno = 0 seqno = 0 - 1 seqno = 0 seqno = 0 seqno = 2 seqno = 0 - 2 Broadcast Medium Window (BMW) Protocol Example 2 1 0 4 3 RTS CTS DATA ACK

  12. Overview • Ad hoc network introduction • Medium access control (MAC) protocol • Broadcast limitation • Broadcast Medium Window (BMW) protocol • The broadcast medium window • Example • Simulation results • Conclusion

  13. Simulation Results • GloMoSim/QualNet network simulator • (http://www.scalable-networks.com) • Application • CBR (512B) • Transport • UDP multicast traffic • Routing • ODMRP • MAC • 802.11 • BMW • Channel • 2Mbps • free-space

  14. On-Demand Multicast Routing Protocol (ODMRP) S S S S D D D D • Sources build routes on demand by flooding • Sources flood JOIN QUERY to multicast receivers • Multicast receivers respond with JOIN REPLY to sources

  15. Traffic Rate Experiment 4 3 0 1 2 9 8 5 6 7 14 13 10 11 12 19 15 18 16 17 24 23 20 21 22 • 25 nodes in grid topology, 3 sources and 6 members • BMW outperforms 802.11 • Under high rate, BMW and 802.11 are comparable • BMW reverts to 802.11 unreliable broadcast

  16. Sources Experiment 4 3 0 1 2 9 8 5 6 7 14 13 10 11 12 19 15 18 16 17 24 23 20 21 22 • 5 members, 2 packets per second, vary number of sources • BMW improves upon 802.11 with moderate number of sources • Under large number of senders, performances are comparable • Large number of senders also implies high network load • BMW reverts to 802.11 again

  17. Members Experiment 4 3 0 1 2 9 8 5 6 7 14 13 10 11 12 19 15 18 16 17 24 23 20 21 22 • 3 sources, 2 packets per second, vary number of members • BMW achieves 100% reliability • 802.11 gradually degrades as the number of members increases

  18. Uniform Experiment • More realistic ad hoc scenario • 25 nodes placed in 1000m x 1000m • Randomly select 5 sources and 5 members • Vary traffic rate • BMW consistently outperforms 802.11

  19. Overview • Ad hoc network introduction • Medium access control (MAC) protocol • Broadcast limitation • Broadcast Medium Window (BMW) protocol • The broadcast medium window • Example • ODMRP with congestion control • Simulation results • Conclusion

  20. Conclusion • Free-space model is very conservative • BMW benefit more from detailed channel model • Drawback of BMW • Increase latency as neighbors and packet loss increase • Solution • Reduce transmit power -> reduce power consumption • Port BMW concept directly into ODMRP • More efficient due to knowledge of forwarding group members

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