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Introduction to Mobile Ad hoc Networks (MANETs)

Introduction to Mobile Ad hoc Networks (MANETs)
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Published Date:22-07-2017
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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, MP3-players •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 Multi-hopDifferences to Wired Networks – Radio (802.11x MAC) •Varying signal-to-noise 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 end-to-end 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 •Network-to-network 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 •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 (Bellman-Ford) – 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 •Multi-Point Relays (MPRs) reduce overhead