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1、1,Note,Due to the time constraints,only a subset of the slides will be discussed during the INFOCOM 2006 tutorial presentation,本资料由-大学生创业|创业|创业网http:/减肥药排行榜|淘宝最好的减肥药|什么减肥药效果最好|减肥瘦身药|http:/,2,Notes,Names in brackets,as in Xyz00,refer to a document in the list of referencesThe handout may not be as re
2、adable as the original slides,since the slides contain colored text and figuresNote that different colors in the colored slides may look identical in the black-and-white handout,本资料由-大学生创业|创业|创业网http:/减肥药排行榜|淘宝最好的减肥药|什么减肥药效果最好|减肥瘦身药|http:/,3,Statutory Warnings,Only most important features of various
3、 schemes are typically discussed,i.e,features I consider as being importantOthers may disagreeMost schemes include many more details,and optimizationsNot possible to cover all details in this tutorialBe aware that some protocol specs have changed several times,and the slides may not reflect the most
4、 current specificationsJargon used to discuss a scheme may occasionally differ from that used by the proposers,4,Coverage,Not intended to be exhaustiveMany interesting papers not covered in the tutorial due to lack of time,5,Tutorial Outline,IntroductionUnicast routingMedium Access Control Performan
5、ce of UDP and TCPSelected security issuesImplementation IssuesStandards activitiesOpen problems,6,Mobile Ad Hoc Networks(MANET)Introduction and Generalities,7,Mobile Ad Hoc Networks,Formed by wireless hosts which may be mobileWithout(necessarily)using a pre-existing infrastructureRoutes between node
6、s may potentially contain multiple hops,8,Mobile Ad Hoc Networks,May need to traverse multiple links to reach a destination,A,B,9,Mobile Ad Hoc Networks(MANET),Mobility causes route changes,A,B,10,Why Ad Hoc Networks?,Ease of deploymentSpeed of deploymentDecreased dependence on infrastructure,11,Man
7、y Applications,Personal area networkingcell phone,laptop,ear phone,wrist watchMilitary environmentssoldiers,tanks,planesCivilian environmentsMesh networkstaxi cab networkmeeting roomssports stadiumsboats,small aircraftEmergency operationssearch-and-rescuepolicing and fire fighting,12,Many Variations
8、,Fully Symmetric Environmentall nodes have identical capabilities and responsibilitiesAsymmetric Capabilitiestransmission ranges and radios may differ battery life at different nodes may differprocessing capacity may be different at different nodesspeed of movementAsymmetric Responsibilitiesonly som
9、e nodes may route packets some nodes may act as leaders of nearby nodes(e.g.,cluster head),13,Many Variations,Traffic characteristics may differ in different ad hoc networksbit ratetimeliness constraintsreliability requirementsunicast/multicast/geocasthost-based addressing/content-based addressing/c
10、apability-based addressingMay co-exist(and co-operate)with an infrastructure-based network,14,Many Variations,Mobility patterns may be differentpeople sitting at an airport loungeNew York taxi cabskids playingmilitary movementspersonal area networkMobility characteristicsspeedpredictabilitydirection
11、 of movementpattern of movementuniformity(or lack thereof)of mobility characteristics among different nodes,15,Challenges,Limited wireless transmission rangeBroadcast nature of the wireless mediumHidden terminal problem(see next slide)Packet losses due to transmission errorsMobility-induced route ch
12、angesMobility-induced packet lossesBattery constraintsPotentially frequent network partitionsEase of snooping on wireless transmissions(security hazard),16,Hidden Terminal Problem,Nodes A and C cannot hear each otherTransmissions by nodes A and C can collide at node BNodes A and C are hidden from ea
13、ch other,17,Research on Mobile Ad Hoc Networks,Variations in capabilities&responsibilities XVariations in traffic characteristics,mobility models,etc.XPerformance criteria(e.g.,optimize throughput,reduce energy consumption)+Increased research funding=Significant research activity,18,The Holy Grail,A
14、 one-size-fits-all solutionPerhaps using an adaptive/hybrid approach that can adapt to situation at handDifficult problemMany solutions proposed trying to address asub-space of the problem domain,19,Assumption,Unless stated otherwise,fully symmetric environment is assumed implicitlyall nodes have id
15、entical capabilities and responsibilities,20,Unicast RoutinginMobile Ad Hoc Networks,21,Why is Routing in MANET different?,Host mobilitylink failure/repair due to mobility may have different characteristics than those due to other causesRate of link failure/repair may be high when nodes move fastNew
16、 performance criteria may be usedroute stability despite mobilityenergy consumption,22,Unicast Routing Protocols,Many protocols have been proposedSome have been invented specifically for MANETOthers are adapted from previously proposed protocols for wired networksNo single protocol works well in all
17、 environmentssome attempts made to develop adaptive protocols,23,Routing Protocols,Proactive protocolsDetermine routes independent of traffic patternTraditional link-state and distance-vector routing protocols are proactiveReactive protocolsMaintain routes only if neededHybrid protocols,24,Trade-Off
18、,Latency of route discoveryProactive protocols may have lower latency since routes are maintained at all timesReactive protocols may have higher latency because a route from X to Y will be found only when X attempts to send to YOverhead of route discovery/maintenanceReactive protocols may have lower
19、 overhead since routes are determined only if neededProactive protocols can(but not necessarily)result in higher overhead due to continuous route updatingWhich approach achieves a better trade-off depends on the traffic and mobility patterns,25,Overview of Unicast Routing Protocols,26,Flooding for D
20、ata Delivery,Sender S broadcasts data packet P to all its neighborsEach node receiving P forwards P to its neighborsSequence numbers used to avoid the possibility of forwarding the same packet more than oncePacket P reaches destination D provided that D is reachable from sender SNode D does not forw
21、ard the packet,27,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Represents that connected nodes are within each others transmission range,Z,Y,Represents a node that has received packet P,M,N,L,28,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Represents transmission of packet P,Represents a
22、 node that receives packet P forthe first time,Z,Y,Broadcast transmission,M,N,L,29,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Node H receives packet P from two neighbors:potential for collision,Z,Y,M,N,L,30,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Node C receives packet P from G an
23、d H,but does not forward it again,because node C has already forwarded packet P once,Z,Y,M,N,L,31,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,Nodes J and K both broadcast packet P to node D Since nodes J and K are hidden from each other,their transmissions may collide=Packet P may not b
24、e delivered to node D at all,despite the use of flooding,N,L,32,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,Node D does not forward packet P,because node D is the intended destination of packet P,M,N,L,33,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Flooding completed Nodes unreacha
25、ble from S do not receive packet P(e.g.,node Z)Nodes for which all paths from S go through the destination D also do not receive packet P(example:node N),Z,Y,M,N,L,34,Flooding for Data Delivery,B,A,S,E,F,H,J,D,C,G,I,K,Flooding may deliver packets to too many nodes(in the worst case,all nodes reachab
26、le from sender may receive the packet),Z,Y,M,N,L,35,Flooding for Data Delivery:Advantages,SimplicityMay be more efficient than other protocols when rate of information transmission is low enough that the overhead of explicit route discovery/maintenance incurred by other protocols is relatively highe
27、rthis scenario may occur,for instance,when nodes transmit small data packets relatively infrequently,and many topology changes occur between consecutive packet transmissionsPotentially higher reliability of data deliveryBecause packets may be delivered to the destination on multiple paths,36,Floodin
28、g for Data Delivery:Disadvantages,Potentially,very high overheadData packets may be delivered to too many nodes who do not need to receive themPotentially lower reliability of data deliveryFlooding uses broadcasting-hard to implement reliable broadcast delivery without significantly increasing overh
29、eadBroadcasting in IEEE 802.11 MAC is unreliableIn our example,nodes J and K may transmit to node D simultaneously,resulting in loss of the packet in this case,destination would not receive the packet at all,37,Flooding of Control Packets,Many protocols perform(potentially limited)flooding of contro
30、l packets,instead of data packetsThe control packets are used to discover routesDiscovered routes are subsequently used to send data packet(s)Overhead of control packet flooding is amortized over data packets transmitted between consecutive control packet floods,38,Dynamic Source Routing(DSR)Johnson
31、96,When node S wants to send a packet to node D,but does not know a route to D,node S initiates a route discoverySource node S floods Route Request(RREQ)Each node appends own identifier when forwarding RREQ,39,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,Represents a node that has received RRE
32、Q for D from S,M,N,L,40,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Represents transmission of RREQ,Z,Y,Broadcast transmission,M,N,L,S,X,Y Represents list of identifiers appended to RREQ,41,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Node H receives packet RREQ from two neighbors:potential for
33、 collision,Z,Y,M,N,L,S,E,S,C,42,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Node C receives RREQ from G and H,but does not forward it again,because node C has already forwarded RREQ once,Z,Y,M,N,L,S,C,G,S,E,F,43,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,Nodes J and K both broadcast RRE
34、Q to node D Since nodes J and K are hidden from each other,their transmissions may collide,N,L,S,C,G,K,S,E,F,J,44,Route Discovery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,Node D does not forward RREQ,because node D is the intended target of the route discovery,M,N,L,S,E,F,J,M,45,Route Discovery in DSR,Des
35、tination D on receiving the first RREQ,sends a Route Reply(RREP)RREP is sent on a route obtained by reversing the route appended to received RREQRREP includes the route from S to D on which RREQ was received by node D,46,Route Reply in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,N,L,RREP S,E,F,J,D,Represents
36、RREP control message,47,Route Reply in DSR,Route Reply can be sent by reversing the route in Route Request(RREQ)only if links are guaranteed to be bi-directionalTo ensure this,RREQ should be forwarded only if it received on a link that is known to be bi-directionalIf unidirectional(asymmetric)links
37、are allowed,then RREP may need a route discovery for S from node D Unless node D already knows a route to node SIf a route discovery is initiated by D for a route to S,then the Route Reply is piggybacked on the Route Request from D.If IEEE 802.11 MAC is used to send data,then links have to be bi-dir
38、ectional(since Ack is used),48,Dynamic Source Routing(DSR),Node S on receiving RREP,caches the route included in the RREPWhen node S sends a data packet to D,the entire route is included in the packet headerhence the name source routingIntermediate nodes use the source route included in a packet to
39、determine to whom a packet should be forwarded,49,Data Delivery in DSR,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,N,L,DATA S,E,F,J,D,Packet header size grows with route length,50,When to Perform a Route Discovery,When node S wants to send data to node D,but does not know a valid route node D,51,DSR Optimization:
40、Route Caching,Each node caches a new route it learns by any meansWhen node S finds route S,E,F,J,D to node D,node S also learns route S,E,F to node FWhen node K receives Route Request S,C,G destined for node,node K learns route K,G,C,S to node SWhen node F forwards Route Reply RREP S,E,F,J,D,node F
41、learns route F,J,D to node DWhen node E forwards Data S,E,F,J,D it learns route E,F,J,D to node DA node may also learn a route when it overhears Data packets,52,Use of Route Caching,When node S learns that a route to node D is broken,it uses another route from its local cache,if such a route to D ex
42、ists in its cache.Otherwise,node S initiates route discovery by sending a route requestNode X on receiving a Route Request for some node D can send a Route Reply if node X knows a route to node DUse of route cache can speed up route discoverycan reduce propagation of route requests,53,Use of Route C
43、aching,B,A,S,E,F,H,J,D,C,G,I,K,P,Q,R Represents cached route at a node(DSR maintains the cached routes in a tree format),M,N,L,S,E,F,J,D,E,F,J,D,C,S,G,C,S,F,J,D,F,E,S,J,F,E,S,Z,54,Use of Route Caching:Can Speed up Route Discovery,B,A,S,E,F,H,J,D,C,G,I,K,Z,M,N,L,S,E,F,J,D,E,F,J,D,C,S,G,C,S,F,J,D,F,E,
44、S,J,F,E,S,RREQ,When node Z sends a route requestfor node C,node K sends back a routereply Z,K,G,C to node Z using a locallycached route,K,G,C,S,RREP,55,Use of Route Caching:Can Reduce Propagation of Route Requests,B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,N,L,S,E,F,J,D,E,F,J,D,C,S,G,C,S,F,J,D,F,E,S,J,F,E,S,RREQ
45、,Assume that there is no link between D and Z.Route Reply(RREP)from node K limits flooding of RREQ.In general,the reduction may be less dramatic.,K,G,C,S,RREP,56,Route Error(RERR),B,A,S,E,F,H,J,D,C,G,I,K,Z,Y,M,N,L,RERR J-D,J sends a route error to S along route J-F-E-S when its attempt to forward th
46、e data packet S(with route SEFJD)on J-D failsNodes hearing RERR update their route cache to remove link J-D,57,Route Caching:Beware!,Stale caches can adversely affect performanceWith passage of time and host mobility,cached routes may become invalidA sender host may try several stale routes(obtained
47、 from local cache,or replied from cache by other nodes),before finding a good routeAn illustration of the adverse impact on TCP will be discussed later in the tutorial Holland99,58,Dynamic Source Routing:Advantages,Routes maintained only between nodes who need to communicatereduces overhead of route
48、 maintenanceRoute caching can further reduce route discovery overheadA single route discovery may yield many routes to the destination,due to intermediate nodes replying from local caches,59,Dynamic Source Routing:Disadvantages,Packet header size grows with route length due to source routingFlood of
49、 route requests may potentially reach all nodes in the networkCare must be taken to avoid collisions between route requests propagated by neighboring nodesinsertion of random delays before forwarding RREQIncreased contention if too many route replies come back due to nodes replying using their local
50、 cacheRoute Reply Storm problemReply storm may be eased by preventing a node from sending RREP if it hears another RREP with a shorter route,60,Dynamic Source Routing:Disadvantages,An intermediate node may send Route Reply using a stale cached route,thus polluting other cachesThis problem can be eas
