Wireless Networks Lecture 28 Mobile Ad hoc Network

Wireless Networks Ü Lecture 28 Ü Mobile Ad hoc Network Ü Dr. Ghalib A. Shah 1

Outlines Ü Introduction ► ► ► What is Ad hoc networks? Characteristic Ad hoc vs. cellular networks Application Challenges Ü Routing Protocol ► Expected Properties of Ad-hoc Routing Protocols ► A taxonomy for routing protocols in Mobile ad ► Some common protocols (DSDV, AODV, DSR, ZRP, TORA) 2

Last Lecture Review Ü Ü Ü Ü Ü Problems with DCF Virtual Carrier Sensing RTC/CTS Protocol Interframe Spacing PCF Fragmentation / Reassembly MAC Frame Format Frame Types Physical Media in Original IEEE 802. 11 3

What is Ad hoc Ü Ad hoc ► For a specific purpose of occasion ► For this case alone Ü IEEE 802. 11 ► a network composed solely of stations within mutual communication range of each other via the wireless media. ► an independent basic service set 4

Ü Mobile distributed multi-hop wireless network (manet) ► a group of mobile, wireless nodes which cooperatively and spontaneously form a network independent of any fixed infrastructure or centralized administration ► A node communicates • • directly with nodes within wireless range indirectly with all other destinations using a dynamically determined multi-hop route though other nodes in the manet 5

The characteristic of ad hoc networks Ü Heterogeneous nodes Ü Self-creating ► not rely on a pre-existing fixed infrastructure Ü Self-organizing ► no predetermined topology Ü Self-administering ► no central control Ü creating a network “on the fly” 6

Ü Ad hoc networks ► infrastructureless ► multiple hop • Radio power limitation, channel utilization, and powersaving concerns ► DCF(distributed coordination function) Ü Cellular networks ► infrastructure-based ► one hop(uplink or downlink) ► PCF(pointed coordination function) 7

Challenges 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Spectrum allocation Self-configuration Medium access control (MAC) Energy efficiency TCP Performance Mobility management Security & privacy Routing protocols Multicasting Qo. S Service Location, Provision, Access 8

Routing Protocols Ü Expected Properties of Ad-hoc Routing Protocols Ü A taxonomy for routing protocols in Mobile ad hoc networks ► ► ► Reactive or On-demand routing protocols Proactive or Table-driven Hybrid Hierarchical Geographical 9

Expected Properties of Routing Ü Ideally an ad hoc network routing protocol should ► ► ► be distributed in order to increase reliability assume routes as unidirectional links be power efficient. consider its security be hybrid protocols be aware of Quality of Service 10

Taxonomy Ü Communication model ► Multi-channel: Channel assignment using low-layer info ► Single channel model Ü Structure ► Are all nodes treated uniformly? ► How are distinguished nodes selected (neighbors or clusterbased)? Ü State information ► Is network-scale topology obtained at each node? Ü Scheduling ► Is route information continually maintained for each destination (proactive or reactive)? 11

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DSDV Ü is based on the idea of Ballman-Ford routing algorithm Ü Every mobile station maintains a routing table that lists ► all available destinations ► the number of hops to reach the destination ► the sequence number assigned by the destination node Ü A station transmits routing table ► periodically ► if a significant change has occurred in its table from the last update sent Ü The routing table updates can be sent in two ways ► full dump ► incremental update 13

Ü Put figure with same illustration of DSR 14

AODV Ü It borrows ► the basic on-demand mechanism of route discovery and route maintenance from DSR ► the use of hop-by-hop routing, sequence numbers, and periodic beacons from DSDV Ü A node periodic broadcasts hello information to maintain the local connectivity Ü It only supports the use of symmetric links 15

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TORA Ü is based on the concept of link reversal Ü finds multiple routes from a source node to a destination node Ü the control messages are localized to a very small set of nodes near the occurrence of a topological change 17

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DSR Ü Ü Ü A node maintains route caches containing the source routes that it is aware of The node updates entries in the route cache as and when it learns about new routes route discovery ► route request packet contains • • • the address of the source the destination a unique identification number ► route reply is generated by • • Ü the destination an intermediate node with current information about the destination route maintenance ► Route error packets are generated at a node when the data link layer encounters a fatal transmission problem ► Acknowledgements, including passive acknowledgments 19

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OLSR Ü OLSR uses multipoint relays to reduce superfluous broadcast packet retransmission and also the size of the LS packets Ü OLSR thus leads to efficient flooding of control messages in the network 21

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OLSR (cont’d) Ü Only the multipoint relays nodes (MPRs) need to forward LS updates Ü OLSR is particularly suited for dense networks Ü In sparse networks, every neighbor becomes a multipoint relay, then OLSR reduces to pure LS protocol 23

ZRP Ü A hybrid routing protocol that combines both proactive and on-demand routing strategies Ü Each node has a predefined zone Ü Inside zones: proactive routing Ü Outside zones: on-demand routing Ü ZRP provides more flexibility 24

Outlines Ü Introduction ► ► ► What is Ad hoc networks? Characteristic Ad hoc vs. cellular networks Application Challenges Ü Routing Protocol ► Expected Properties of Ad-hoc Routing Protocols ► A taxonomy for routing protocols in Mobile ad ► Some common protocols (DSDV, AODV, DSR, ZRP, TORA) 25