routing and location management in mobile ad-hoc networks

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Routing and Location Management in Mobile Ad-hoc Networks. By Sumesh J. Philip (09/20/2001). Contents. Introduction Routing Protocols Table Driven (WRP, DSDV) On Demand (DSR, AODV, TORA) Performance Evaluation Geographic (LAR, DREAM) - PowerPoint PPT Presentation

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  • Routing and Location Managementin Mobile Ad-hoc Networks BySumesh J. Philip(09/20/2001)

  • ContentsIntroductionRouting ProtocolsTable Driven (WRP, DSDV)On Demand (DSR, AODV, TORA)Performance EvaluationGeographic (LAR, DREAM)Location Management for Large Scale Networks (GLS, SLURP, SLALOM)References

  • Mobile Ad-Hoc NetworkCollection of mobile nodes forming a networkNo centralized administration or standard support servicesHighly co-operative, each host is an independent routerHosts use wireless RF transceivers as network interface

    Conferences/Meetings

    Search and Rescue

    Disaster Recovery

    Automated Battlefields

  • MaNet Constraints and IssuesLack of a centralized entityNetwork topology changes frequently and unpredictablyRouting and Mobility ManagementChannel access/Bandwidth availabilityHidden/Exposed station problemLack of symmetrical linksPower limitation

  • Conventional Routing Protocols ?Not designed for highly dynamic, low bandwidth networksCount-to-infinity problem and slow convergenceLoop formation during temporary node failures and network partitionsProtocols that use flooding techniques create excessive traffic and control overhead

  • MaNet ProtocolsProactive ProtocolsTable drivenContinuously evaluate routesNo latency in route discoveryLarge capacity to keep network information currentA lot of routing information may never be used!

    Reactive ProtocolsOn DemandRoute discovery by some global searchBottleneck due to latency of route discovery May not be appropriate for real-time communication

  • Wireless Routing Protocol (WRP)A Path finding algorithm; uses predecessor to destination in the shortest pathEliminates the Count-to-infinity problem and converges fasterNeighbor connectivity via periodic Hello messagesUpdate messages sent upon detecting a change in neighbor link

  • Each node i maintains a Distance table (iDjk), Routing table (Destination Identifier, Distance iDj , Predecessor Pj ,the successor Sj), link cost table (Cost, Update Period) Processing Updates and creating Route TableUpdate from k causes i to re-compute the distances of all paths with k as the predecessorFor a destination j, a neighbor p is selected as the successor if p->j does not include i, and is the shortest path to j

  • OperationJKIB(0, J)(2, K)(2, K)(1, K)X11101510(, K)(11, B)

  • Destination Sequenced Distance Vector (DSDV)Each Route is tagged with a sequence number originated by destinationHosts perform periodic & triggered updates, issuing a new sequence numberSequence number indicates the freshness of a routeRoutes with more recent sequence numbers are preferred for packet forwardingIf same sequence number, one having smallest metric used

  • Topology changesBroken links assigned a metric of Any route through a hop with a broken link is also assigned a metric of routes are assigned new sequence numbers by any host and immediately broadcast via a triggered updateIf a node has an equal/later sequence number with a finite metric for an route, a route update is triggered

  • DSDV Operation

  • Damping FluctuationsRoutes preferred if later sequence numbers, or smaller metric for same sequence numbersProblem : Table fluctuations if worse metrics are received first, causing a ripple of triggered updatesSolution : Use average settling time as a parameter before advertising routesTantamount to using two tables, one for forwarding packets and another for advertising routes

  • Dynamic Source Routing (DSR)Each packet header contains a route, which is represented as a complete sequence of nodes between a source-destination pairProtocol consists of two phases route discoveryroute maintenanceOptimizations for efficiencyRoute cachePiggybackingError handling

  • DSR Route DiscoverySource broadcasts route request (id, target) Intermediate node actionDiscard if id is in or node is in route recordIf node is the target, route record contains the full route to the target; return a route replyElse append address in route record; rebroadcastUse existing routes to source to send route reply; else piggyback

  • DSR Route MaintenanceUse acknowledgements or a layer-2 scheme to detect broken links; inform sender via route error packetIf no route to the source existsUse piggybackingSend out a route request and buffer route error Sender truncates all routes which use nodes mentioned in route errorInitiate route discovery

  • Optimizations for efficiencyRoute CacheUse cached entries for during route discoveryPromiscuous mode to add more routesUse hop based delays for local congestionMust be careful to avoid loop formationNon propagating RREQs

  • OptimizationsPiggybackingData piggybacked on route request Packet Problem : route caching can cause piggybacked route replies to be discardedImproved Error Handlingwhen network becomes partitioned, buffer packets and use exponential back-off for route discoveryListen to route replies promiscuously to remove entriesUse negative information to ignore corrupt replies

  • Ad-hoc On DemandDistance Vector (AODV) On demand protocol that uses sequence numbers (DSDV) to build loop free routesKey difference from DSR is that source route is no longer requiredPath discoveryReverse Path setupForward path setupTable management and path maintenanceLocal connectivity management

  • AODV Reverse path setupCounters : Sequence number, Broadcast idReverse PathBroadcast route request (RREQ) < source_addr, source_sequence-# , broadcast_id, dest_addr, dest_sequence_#, hop_cnt >RREQ uniquely identified by Route reply (RREP) if neighbor is the target, or knows a higher dest_sequence_#Otherwise setup a pointer to the neighbor from whom RREQ was receivedMaintain reverse path entries based on timeouts

  • AODV Forward path setupRREQ arrives at a node that has current route to the destination ( larger/same sequence number) unicast request reply (RREP) to neighborRREP travels back to the source along reverse path each upstream node updates dest_sequence_#, sets up a forward pointer to the neighbor who transmit the RREP

  • AODV OperationDS

  • Protocol MaintenanceRoute Table managementRoute request expiration timer purges reverse paths that do not lie on active routeActive neighbor relays a packet within active_route_timeoutRoute cache timer purges inactive routesNew routes preferred if higher destination sequence number or lower metric

  • AODV MaintenancePath maintenanceUpon link breakage, affected node propagates an unsolicited RREP to all upstream nodesSource may restart route discovery processLocal connectivity managementBroadcasts used to update local connectivity informationInactive nodes in an active path required to send hello messages

  • Temporally OrderedRouting Algorithm (TORA)Link reversal algorithmDestination oriented Directed Acyclic Graph (DAG)Full/Partial reversal of linksAssigns a reference level (height) to each nodeAdjust reference level to restore routes on link failureMultiple routes to destination; route optimality not importantQuery, Update, Clear packets used for creating, maintaining and erasing routes

  • Creating RoutesCABEG (DEST)FHDQRY

  • Route MaintenanceCABEG (DEST)FHDUPDXUPDUPD

  • Erasing Invalid Routes

  • Performance AnalysisSimulation EnvironmentNetwork Simulator, 50 nodes in a 1500x300m rectangular flat gridRandom waypoint mobilityConstant bit rate trafficAddress resolution : ARP implementation in BSD UnixMedium Access Control : IEEE 802.11 Physical Layer model : combines both free space and two ray ground reflection modelProtocols studied : DSDV(SQ), AODV, DSR, TORA

  • Performance AnalysisMetricsPacket Delivery Ratio : Ratio of number of packets generated by CBR sources to that received by CBR sinks at destinationRouting Overhead : number of routing packets sent; each transmission counts as one transmissionPath Optimality : Difference between length of actual path took and the length of the shortest path

  • Packet Delivery Ratio95-100% in most cases for DSR, AODVStale route entries in DSDV cause dropsShort lived loops in TORA as part of link reversalAll protocols perform well when there is low node mobility

  • Routing Overhead (packets)Route caching and non-propagating RREQs in DSRTORASum of mobility dependant, independent overhead for TORACongestive collapse Nearly constant for DSDV due to periodic updates

  • Routing Overhead (Bytes)DSR more expensive than AODV except at high mobilitySmaller packets in AODV, may be more expensive in terms of media access, power and network utilization

  • Path OptimalityDSDV, DSR use routes close to optimalTORA not designed to find shortest pathTORA, AODV use paths close to optimum when node mobility is low

  • Geographic RoutingNot many invariants to play with (IP address, local connectivity)Nodes physically located closer likely to be connected by a small number of radio hopsPossible to obtain node location via a GPS systemGeographic forwardingPacket header contains the destinations locationMost forward with fixed radius

  • Distance Routing EffectAlgorithm for Mobility (DREAM)Proactively disseminate location informationDistance Effect :Closer nodes are updated more frequentlyage field in location updateMobility Effect :rate of location update controlled by mobilityNo bandwidth wastage for no movement Geographic forwardingIf no entry for destination in table, floodOtherwise forward data to m neighbors in the direction of destination

  • Location Aided Routing (LAR)On Demand protocol; used restricted flooding for locating destination Flooding is restricted to a request zone, defined by an