MAC Reliable Broadcast in Ad Hoc NetworksKen Tang, Mario GerlaUniversity of California, Los Angeles(ktang, [email protected])Overview§ Ad hoc network introduction§ Medium access control (MAC) protocol§ Broadcast limitation§ Broadcast Medium Window (BMW) protocol§ The broadcast medium window§ Example§ Simulation results§ ConclusionAd Hoc Network IntroductionStandard base station cellular networksInstant infrastructure, multi-hop wireless ad hoc networksBase BaseBaseOverview§ Ad hoc network introduction§ Medium access control (MAC) protocol§ Broadcast limitation§ Broadcast Medium Window (BMW) protocol§ The broadcast medium window§ Example§ Simulation results§ ConclusionAn Example of Random Access Scheme (IEEE 802.11) –Unicast ModeB. Node 0 transmits RTS to node 4120354A. Collision avoidance6C. Node 4 transmits CTS and node 6 attempts an RTSRTSCTSDATAACKD. Node 0 transmits DATAE. Node 4 transmits ACKRemoteSteps: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!An Example of Random Access Scheme (IEEE 802.11) –Broadcast ModeB. Node 0 transmits DATA120354A. Collision avoidance6DATASteps:Overview§ Ad hoc network introduction§ Medium access control (MAC) protocol§ Broadcast limitation§ Broadcast Medium Window (BMW) protocol§ The broadcast medium window§ Example§ Simulation results§ ConclusionBroadcast 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 broadcastingThe 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 transmissionBroadcast Medium Window (BMW) Protocol Example12034RTSCTSDATAACKseqno = 0seqno = 0 - 1seqno = 0 - 2seqno = 0seqno = 0seqno = 0 - 1seqno = 1seqno = 2Overview§ Ad hoc network introduction§ Medium access control (MAC) protocol§ Broadcast limitation§ Broadcast Medium Window (BMW) protocol§ The broadcast medium window§ Example§ Simulation results§ ConclusionSimulation 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-spaceSDSDSDSD§ Sources build routes on demand by flooding§ Sources flood JOIN QUERY to multicast receivers§ Multicast receivers respond with JOIN REPLY to sourcesOn-Demand Multicast Routing Protocol (ODMRP)Traffic Rate Experiment25 Nodes Traffic Rate Experiment00.20.40.60.8110100200300400500Packet Interdeparture Rate (ms)Packet Delivery RatioBMW802.11§ 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 broadcast01 23456 7891011 1213141516 1718192021 222324Sources Experiment§ 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 againSources Experiment00.20.40.60.811 4 8 12 16Number of SourcesPacket Delivery RatioBMW802.1101 23456 7891011 1213141516 1718192021 222324Members Experiment§ 3 sources, 2 packets per second, vary number of members§ BMW achieves 100% reliability§ 802.11 gradually degrades as the number of members increasesMembers Experiment00.20.40.60.811 4 8 12 16Number of MembersPacket Delivery RatioBMW802.1101 23456 7891011 1213141516 1718192021 222324Uniform 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 802.11Uniform Experiment00.20.40.60.811.250MS 100MS 150MS 200MS 250MS 300MS 350MS 400MS 450MS 500MSPacket Interdeparture RateBMW802.11Overview§ 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§ ConclusionConclusion§ 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
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