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1、Mobile Ad Hoc NetworksNitin H. Vaidya Texas A&M Universityvaidyacs.tamu.edu http:/www.cs.tamu.edu/faculty/vaidya/ 2000 Nitin Vaidya1NotesgFor a larger set of tutorial slides, please go tohttp:/www.cs.tamu.edu/faculty/vaidyaand follow the link to Seminars2NotesgNames in brackets, as in Xyz00, refer t
2、o a document in the list of referencesgThe handout may not be as readable as the original slides, since the slides contain colored text and figures iNote that different colors in the colored slides may look identically black in the black-and-white handout3Tutorial OutlinegIntroductiongUnicast routin
3、ggMedium Access Control gPerformance of UDP and TCPgSecurity IssuesgImplementation IssuesgStandards activitiesgOpen problems4NotesgOnly most important features of various schemes are typically discussedgMost schemes include many more details, and optimizations iNot possible to cover all details in t
4、his tutorialgBe aware that some protocol specs have changed several timesgJargon used to discuss a scheme may occasionally differ from that used by the proposers5Mobile Ad Hoc Networks (MANET)Introduction and Generalities6Mobile Ad Hoc NetworksgFormed by wireless hosts which may be mobilegWithout (n
5、ecessarily) using a pre-existing infrastructuregRoutes between nodes may potentially contain multiple hops7Mobile Ad Hoc NetworksgMay need to traverse multiple links to reach a destination8Mobile Ad Hoc Networks (MANET)gMobility causes route changes9Why Ad Hoc Networks ?gEase of deploymentgSpeed of
6、deploymentgDecreased dependence on infrastructure10Many ApplicationsgPersonal area networking icell phone, laptop, ear phone, wrist watchgMilitary environments isoldiers, tanks, planesgCivilian environments itaxi cab network imeeting rooms isports stadiums iboats, small aircraftgEmergency operations
7、 isearch-and-rescue ipolicing and fire fighting11Many VariationsgFully Symmetric Environment iall nodes have identical capabilities and responsibilitiesgAsymmetric Capabilities itransmission ranges and radios may differ ibattery life at different nodes may differ iprocessing capacity may be differen
8、t at different nodes ispeed of movementgAsymmetric Responsibilities ionly some nodes may route packets isome nodes may act as leaders of nearby nodes (e.g., cluster head)12Many VariationsgTraffic characteristics may differ in different ad hoc networks ibit rate itimeliness constraints ireliability r
9、equirements iunicast / multicast / geocast ihost-based addressing / content-based addressing / capability-based addressinggMay co-exist (and co-operate) with an infrastructure- based network13Many VariationsgMobility patterns may be different ipeople sitting at an airport lounge iNew York taxi cabs
10、ikids playing imilitary movements ipersonal area networkgMobility characteristics ispeed ipredictabilitydirection of movementpattern of movement iuniformity (or lack thereof) of mobility characteristics among different nodes14ChallengesgLimited wireless transmission rangegBroadcast nature of the wir
11、eless medium iHidden terminal problem (see next slide)gPacket losses due to transmission errorsgMobility-induced route changesgMobility-induced packet lossesgBattery constraintsgPotentially frequent network partitionsgEase of snooping on wireless transmissions (security hazard)15Hidden Terminal Prob
12、lemBCANodes A and C cannot hear each otherTransmissions by nodes A and C can collide at node BNodes A and C are hidden from each other16Research on Mobile Ad Hoc NetworksVariations in capabilities & responsibilitiesX Variations in traffic characteristics, mobility models, etc.X Performance criteria
13、(e.g., optimize throughput, reduce energy consumption)+Increased research funding= Significant research activity17The Holy GrailgA one-size-fits-all solution iPerhaps using an adaptive/hybrid approach that can adapt to situation at handgDifficult problemgMany solutions proposed trying to address a s
14、ub-space of the problem domain18AssumptiongUnless stated otherwise, fully symmetric environment is assumed implicitly iall nodes have identical capabilities and responsibilities19Unicast Routing in Mobile Ad Hoc Networks20Why is Routing in MANET different ?gHost mobility ilink failure/repair due to
15、mobility may have different characteristics than those due to other causesgRate of link failure/repair may be high when nodes move fastgNew performance criteria may be used iroute stability despite mobility ienergy consumption21Unicast Routing ProtocolsgMany protocols have been proposedgSome have be
16、en invented specifically for MANETgOthers are adapted from previously proposed protocols for wired networksgNo single protocol works well in all environments isome attempts made to develop adaptive protocols22Routing ProtocolsgProactive protocols iDetermine routes independent of traffic pattern iTraditional link-state and distance-vector routing protocols are proactivegReactive protocols iMaintain routes only if neededgHybrid protocols23Trade-OffgLatency of route
