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Introduction to Mobile Ad hoc Networks (MANETs)

Introduction to Mobile Ad hoc Networks (MANETs)
Introduction to Mobile Ad hoc Networks (MANETs) Advanced Computer NetworksOutline •Ad hoc networks – Differences to other networks •Applications •Research areas •Routing •Other research areasEnabling Technologies •Ubiquitous computing devices with WiFi – Laptops – PDAs – Cameras, MP3players •Medium Access Control (MAC) – IEEE 802.11x – BluetoothThe Internet – A hierarchy of Networks Internet core Server AS AS End host LAN AS LANHow are mobile ad hoc networks different Ad hoc ≈ “for a particular purpose”, improvised •No infrastructure – flat network •Radio communication – shared medium • Every computer or device (node) is a router as well as end host •Nodes are in general autonomous •Mobility – dynamic topology •Limited energy and computing resourcesDifferences to other Wireless Networks Ad hoc network Bluetooth/802.11 Ad hoc mode Wireless LAN 802.11 Mobile ad hoc network (MANET) 802.11 MultihopDifferences to Wired Networks – Radio (802.11x MAC) •Varying signaltonoise ratio •Different rates = different transmission ranges •CSMA •Channel contention • Obstructions •Interference, e.g., “hidden terminals” CollisionDifferences to Wired Networks The Effect of a Shared Channel 1500 1400 1300 Bandwidth decreases 1200 1100 asymptotically with hop 1000 count 900 800 700 600 500 400 •Nodes interfere with next 300 200 hops 100 1 2 3 4 5 6 7 8 9 10 •Over longer paths Number of hops Source:Holland et al. 2002 interference is constant 1 2 3 4 TCP Throughput (Kbps)MANET Applications Military •Unknown terrain •Limit the range of communication – Directional antennas •Destroyed infrastructureMANET Applications – Disaster Relief •Disaster relief – Earthquakes, tsunamis, hurricanes – Wiped out infrastructure – Search rescueMANET Applications – Economic Commercial •Community Mesh networks •Access extensions •Personal Area Networks (PANs) •Ad hoc Gaming (on subway, cafés, etc)MANET Research Areas •Routing •Path metrics – hop count, SNR, RTT, geographical •Energy conservation •QoS •Multicast •Security •Self configuration •Cooperation and Incentive mechanisms MANET Routing Goals •Finding endtoend paths/routes •Scaling – minimize overhead •Loop free •Route maintenanceSo why not just use Internet protocols (OSPF, RIP) •Limited node capacity – Nodes are not dedicated routers •Higher loss rate •Links are not binary on/off – varying quality •Frequent topology changes •AddressingMANET Routing Challenges •Flat addressing – no hierarchy – scaling issues •Mobility – frequently changing topology – adaptability, reactiveness •Heterogeneity – All nodes are not made equal •Networktonetwork connectivity – Internet accessTaxonomy of Ad hoc Routing Protocols Unicast Ad hoc Routing Flat Hierarchical Geographic Reactive Proactive HybridFlat Routing •Proactive: – Global network view • Disseminates routing information continuously • A route is available when needed – Slow convergence •Reactive: – Partial network view • Only active (or cached) routes are known • Routes discovered when needed – Reacts quickly to topology changes •Hybrid – achieves scalingIETF Routing Standardization – The MANET Working Group http://www.ietf.org/html.charters/manetcharter.html •Standardizing MANET routing protocols (since 1995) •Incorporating experiences from previous research on four routing protocols: – OLSR – TBRPF – AODV – DSR •Current candidates: – One proactive – OLSRv2 – One reactive – DYMO (AODVv2)Classical Routing Approaches •Distance vector (RIP) – Distributed calculation of topology (BellmanFord) – Routing information aggregated in vectors dest, hop count •Link state (OSPF) – All nodes propagate their link state to all other nodes – Local calculation on complete network graph to find shortest path (Dijkstra)Optimized Link State Routing (OLSR) •Proactive •Traditional link state protocol – optimized for MANETs •MultiPoint Relays (MPRs) reduce overheadAd hoc Ondemand Distance Vector (AODV) •Reactive protocol (not really distance vector despite name) •Route discovery (route request route reply) – Flooding to discover new routes (when needed) •Route maintenance – Only active routes in routing table •HELLO messages monitor links •Sequence numbers in control messages to avoid routing loops •Explicit route error notification (RERR)Route Discovery Example (AODV) RREP D RREQ SDynamic Source Routing (DSR) •A “reactive link state protocol” •Route discovery similar to that in AODV – accumulates source route during discovery •Source routing (really source forwarding) – No hopbyhop forwarding state in nodes – Append full route to all data packets •Promiscuous operation – Cache routing information (link state) – Automatic route shortening •Packet salvagingRoute Discovery Example (DSR) S123 D 3 S1234 S12 4 RREP S1234D 2 S1 6 5 1 RREQ S S S1234DPerformance Evaluation •Simulation – Idealized environment, simplified models •Emulation – Reduce impact of radio, emulate mobility •Real world experiments – Repeatability issuesMANET Research at Uppsala University •Experimental approach •Implementing routing protocols – AODVUU – DSRUU – LUNAR •Making ad hoc work in the real world – Communication gray zones •Real world Experiments – APE Testbed – Comparison to simulation and evaluationDifferences Between Simulation and Real World Communication Gray zones •Broadcast and unicast TX ranges are different •Broadcast HELLO messages give false connectivitySimulation vs. Emulation vs. Real World Roaming Node Scenario – Ping TrafficSome Security Issues in MANETs •Passive eavesdropping •Denial of Service (DoS) – black holes •Signaling attacks •Flow disruption •Resource depletion •Data integrity attacksIncentive Mechanisms •Why should I forward someone else's packets – Drains battery – Reduces bandwidth – Consumes CPU •Approaches – Game Theory models – Economical modelsInternet Connectivity •How to interface with the Internet – Addressing problems, flat vs. hierarchical – Multiple gateways – Home vs foreign networks – Mobile IP Integration – Gateway discovery/selectionInternet Connectivity Example
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