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Transpo rt Protocols in

Transpo rt Protocols in. Wireless Sensor Networks. Kevin Mendes Lakehead University. Topics to be Covered. Trans p ort Protocol O bjectives Draw b acks of TCP in W SNs Design Guid e li n es ( Performa n ce Metrics ) Cong e stion Control & its Causes Loss Recove r y.

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Transpo rt Protocols in

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  1. TransportProtocolsin WirelessSensorNetworks Kevin Mendes Lakehead University

  2. Topics to be Covered • TransportProtocol Objectives • Drawbacksof TCPin WSNs • DesignGuidelines (PerformanceMetrics) • CongestionControl & its Causes • LossRecovery

  3. TransportProtocol Objectives • Transportprotocolsare usedto: • Mitigatecongestion, • Reducepacketloss, • Providefairnessin bandwidthallocation, • Guaranteeend-to-endreliability. • Thetraditionaltransport protocols (i.e.,UDPandTCP) cannot be directlyimplementedfor WSNs • UDPdoesnotprovidedeliveryreliabilitythatisoftenneeded formanysensorapplications, • Nordoesitofferflow andcongestioncontrolthatcanlead to packetlossandunnecessaryenergyconsumption.

  4. Drawbacksof TCPin WSNs • Overheadassociatedwith TCP connection • establishment • Flow andcongestioncontrol mechanismsinTCP • Resultin unfairbandwidthallocationanddatacollections. • TCPassumesthatpacketlossisduetocongestion • TCPhasadegradedthroughputin wirelesssystems • TCPrelieson end-to-endretransmission • Consumesmoreenergyandbandwidththanhop-by-hop • retransmission. • TCPguaranteessuccessfultransmissionof packets • Isnotalwaysnecessaryforevent-drivenapplicationsin • sensornetworks.

  5. DesignGuidelines • In WSNsseveralnewfactors,canresultin congestion: • Convergentnature ofupstreamtraffic • Limited wirelessbandwidth • TworeasonsofpacketlossinWSNs: • Packet loss dueto congestioninintermediate nodes • Packet loss dueto bit-error rate(number of bit errors divided by the total number of transferred bits during a studied time interval)inwirelesschannel • TwomajorproblemsthatWSNtransport protocolsneedtocopewith: • Congestion • Packet loss.

  6. PerformanceMetrics • TransportprotocolsforWSNsshouldprovide: • End-to-endreliability • End-to-endQoS • Performancemetrics: • Energy efficiency, • Reliability, • QoS • Packet-lossratio, • Packet-delivery • Latency • Fairness.

  7. PerformanceMetrics: EnergyEfficiency • Sensornodeshave limitedenergy. • Transportprotocolsshouldmaintainhighenergy efficiency • Tomaximizesystemlifetime. • Forloss-sensitiveapplications, • Packetlossleadstoretransmission • Inevitableconsumptionofadditional batterypower • Therefore,severalfactorsneedtobecarefully • considered, • Numberofpacketretransmissions, • Distance(e.g.,hop)foreachretransmission, • Overheadassociatedwithcontrolmessages.

  8. PerformanceMetrics: Reliability • ReliabilityinWSNscanbeclassifiedintothe • following categories: • Packet reliability: • Applicationsareloss-sensitiveandrequiresuccessful transmissionofall packetsorata certainsuccessratio. • Event reliability: • Applicationsrequireonly successfuleventdetection,but • notsuccessfultransmissionofallpackets. • Destination-relatedreliability: • Messagesmightneedtobe deliveredtosensornodes: • Thatarein aspecificsubarea • Thatareequippedwithaparticularsensortype.

  9. PerformanceMetrics: QoSMetrics • QoSmetricsinclude: • Bandwidth, • Latencyor delay, • Packet-loss ratio. • Dependingontheapplication,thesemetricsor theirvariantscouldbeused forWSNs. • TargettrackingApplication: • Generatehigh-speeddatastreams • Requirehigherbandwidth • Fora delay-sensitiveapplication: • Mayalsorequiretimelydeliverydata.

  10. PerformanceMetrics: Fairness • What if Sensornodesarescatteredinageographical • Area? • Many-to-oneconvergentnatureofupstream • traffic: • Itis difficult forsensornodesthatare farawayfrom thesinkto transmitdata. • Transportprotocolsneedtoallocate • bandwidthfairlyamongallsensornodes • Sink can obtaina fairamount of data fromall the sensor nodes.

  11. CongestionControl  Closed-loopcontrol feedback Feedbackshouldbefrequent,butnottoomuchotherwisetherewillbeoscillations Cannotcontrolthebehaviorwith atimegranularitylessthanthefeedbackperiod

  12. EffectofCongestion • Packetloss • Retransmission • Reducedthroughput • Congestioncollapsedue to • Unnecessarilyretransmittedpackets • Undeliveredorunusablepackets

  13. CongestionControlintheInternet improving the efficiency of TCP/IP networks by reducing the number of packets that need to be sent over the network. ActiveQueue Management(AQM) TCPCongestionControl

  14. CausesFor Congestion in WSNs • Duetothepacket-arrivalrateexceeding • thepacket-servicerate. • Thisismorelikelytooccuratsensornodes • closeto thesink • Link-levelperformanceaspectssuchas: • Contention, • Interference, • Bit-errorrate. • Thistypeof congestionoccursonthelink.

  15. Typesof Congestionin WSNs • NodeLevel Congestion: • It isduetothepacket-arrival rateexceedingthepacket- servicerate. • Thisis morelikelytooccur at sensornodesclosetothe sink. • LinkLevel Congestion: • It aspects suchas contention,interference,and bit-errorrate.

  16. EffectsofCongestion in WSNs • Energy: • Wastethelimitednodeenergy • ApplicationQoS: • Degrade reliabilityandapplicationQoS • Buffer overflow • Larger queuingdelays • Higherpacket loss. • Degrade linkutilization. • ItresultsintransmissioncollisionsifCSMA,is • used • increases packet-servicetime • wastes energy.

  17. CongestionControlApproaches • Therearetwogeneralapproachesto • controlcongestion: • Networkresourcemanagement: • triesto increasenetwork resource to mitigate congestion • Trafficcontrol: • impliesto control congestionthroughadjusting trafficrate atsource nodesor intermediates nodes

  18. TrafficControlMethods • End-to-end: • Can imposeexact rate adjustment at each source node • Simplify the designat intermediatenodes • Itresults inslowresponseandrelieshighlyonthe • round-triptime (RTT). • Hop-by-hop: • Ithas fasterresponse. • Difficultto adjust thepacket forwardingrate at intermediate nodes • BecausepacketforwardingrateisdependentonMAC • protocolandcouldbe variable.

  19. CongestionControlParts • Congestiondetection • Monitor buffer/queue size • Monitor channelbusy time, estimatechannel’sload • Monitor theinter-packet arrivaltime (data,ctrl) • Congestionnotification • Explicitcongestionnotificationinpacketheader,then broadcast (but then energy-consuming!) • RateAdjustment • Dynamic reportingrate dependingon congestionlevel • In-networkdatareductiontechniques(agressive • aggregation)oncongestion

  20. CongestionDetection • In TCP: • Congestionis observedat theendnodesbasedon atimeoutor redundantAcknowledgments. • In WSNs: • Proactivemethods are preferred. • Congestion indicators: • Queuelength • Packet service time • Theratioof packet servicetimeover packet • interarrivaltime

  21. CongestionNotification • Propagationofcongestioninformationfromthe • congested node • Totheupstreamsensornodes • Tothesourcenodesthatcontributetocongestion • Congestioninformation • CongestionNotification(CN)bit, • Ormoreinformationsuchasallowable datarate,orthe congestiondegree. • Disseminatingcongestioninformation: • Explicit • Usesspecialcontrol messagesto notifytheinvolvedsensor nodes of congestion • Implicit • Piggybackscongestioninformationin normaldata packets.

  22. RateAdjustment • Uponreceivingacongestion indication,a • sensornodecanadjustitstransmissionrate. • If a singleCNbitisused: • AdditiveIncreaseMultiplicativeDecrease(AIMD) • If additionalcongestion informationis available: • Accuraterate adjustmentcanbe implemented

  23. LossRecovery • Reasonsofpacket loss in wirelessenvironments: • Congestion • Biterror • nodefailure, • wrongoroutdatedroutinginformation, • Energydepletion. • How to overcomethisproblem: • Increasethesourcesendingrate • Workswellforguaranteeingevent reliability • Isnotenergyefficient • Introduceretransmission-basedlossrecovery. • Ismoreactiveandenergyefficient • Can be implementedat both thelinkand transportlayers. • Link-layerloss recoveryis hop-by-hop,whilethetransportlayer recoveryis usuallydoneend-to-end.

  24. LossDetection andNotification • Acommonmechanismis toincludea sequencenumberineachpacket header. • Thecontinuityofsequencenumbers can beusedtodetectpacketloss. • Lossdetectionandnotificationcanbe: • End-to-end • Hop-by-hop.

  25. End-to-EndApproaches • End-points(destinationorsource)are • responsibleforlossdetectionandnotification. • Drawbacks • Isnotenergy efficient. • Thecontrolmessageswould utilize areturnpath consistingofseveralhops • Control messagestravelthroughmultiplehops • Couldbe lostwitha highprobabilityduetoeitherlinkerror orcongestion. • Leads toend-to-endretransmissionsfor loss • recovery.

  26. Hop-by-hopLossDetectionand Notification • Intermediatenodesdetectandnotifypacket • loss. • Apairofneighboringnodesareresponsible • for lossdetection. • Is moreenergyefficient. • Twocategories: • Receiver-based • Receiverinferspacketlosswhenitobservesout-of- sequencepacketarrivals. • Senderbased • Senderdetectspacketlossoneitheratimer-basedor overhearingmechanism.

  27. MethodstoNotify theSender • Specialcontrolmessages: • ACK(Acknowledgment) • NACK(NegativeACK) • PiggybackingACKinthepacket header • IACK(ImplicitACK) usingoverhearing • Avoids control messageoverhead • Moreenergyefficient. • Sensor nodesmusthavethecapabilitytooverhearthephysical • channel. • Isnotfeasiblewhen: • Transmissionis corrupt • Channelisnotbidirectional • Sensornodesaccess thephysicalchannelusingTimeDivision MultipleAccess(TDMA)-basedprotocols

  28. Retransmission-BasedLoss Recovery • End-to-end • The source performsretransmission. • Hop-byhop. • Anintermediatenodethat interceptsloss notification searchesitslocalbuffer. • Ifitfinds a copy of thelostpacket, it retransmits the packet. • Otherwiseitrelayslossinformation upstreamto • otherintermediatenodes.

  29. Comparisons • End-to-end retransmission: • Thecachepointis thesourcenode. • Hasalongerretransmissiondistance • Allowsforapplication-dependentvariablereliabilitylevels • Hop-by-hopretransmission: • Thecachepointcouldbethepredecessornodeoftheloss point. • Ismoreenergy-efficient • Requiresintermediatenodestocachepackets. • Ispreferredif100percentpacketreliabilityis required • Cannotassuremessagedeliveryin thepresenceofnode • failure

  30. IssuesRelated toHop-by-hop Retransmission • Immediateretransmission • Retransmissioncanbe triggeredimmediatelyuponthe detectionofa packetloss. • Resultsin shorterdelay • Ifpacketlossiscausedbycongestionitcouldaggravatethe • congestionsituationandcausemorepacketlosses. • Distributed TCP Cache(DTC) • Giventhelimited memoryin sensornodes,packetsmayonly • needtobecachedatselectednodes. • Howtodistributecachedpacketsamongasetofnodes? • Itbalancethebufferconstraintsandretransmissionefficiency byusingprobability-basedselectionforcachepoints.

  31. DesignGuidelines • Severalfactorsmustbetaken into consideration: • Topology • Diversityofapplications • Trafficcharacteristics • Resourceconstraints • Transportprotocolscomponents • Congestioncontrol • Lossrecovery • Twoapproaches • Designseparateprotocolsoralgorithms,respectively,for congestioncontrolandlossrecovery. • Providescongestionandlosscontrolin an integratedway • Thejointuseofthesetwoprotocolsmayprovidethefull • functionalityrequiredbythetransportprotocolsforWSNs.

  32. TheExisting TransportProtocolsfor WSNS • ProtocolsforCongestionControl • CongestionDetectionandAvoidance(CODA) • Control andFairness (CCF) • PumpSlowlyFetch Quickly(PSFQ) • Priority-basedCongestionControlProtocol(PCCP) • Siphon • Adaptive Rate Control(ARC) • Trickle • ProtocolsforReliability • ReliableMulti-Segment Transport(RMST) • ReliableBurstyConvergecast(RBC) • Event-to-Sink ReliableTransport (ESRT) • GARUDA • ProtocolsforCongestionControlandReliability • Sensor TransmissionControlProtocol(STCP)

  33. WSNCongestionControlProtocols • CCF : • Packetservicetime • Implicit • Exact hop-by-hoprate adjustment • STCP: • Queuelength, • Implicitcongestionnotification, • AIMD-like end-to-endrate adjustment • Fusion: • Queuelength, • Implicitcongestionnotification, • Stop-and-starthop-by-hoprate • adjustment • CODA: • Queuelengthand channel status, • Explicitcongestionnotification, • AIMD-likeend-to-endrate • adjustment • PCCP: • Packetinterarrivaltime and packetservicetime, • Implicitcongestionnotification, • Exact hop-by-hoprate • adjustment • ARC: • Theevent if thepackets are successfully forwardedor not, • Implicitcongestionnotification, • AIMD-like hop-by-hoprate adjustment

  34. References A Survey of Transport Protocols for Wireless Sensor Networks: Chong gang Wang and KazemSohraby, University of Arkansas Link:http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01637930

  35. Thank You • Any Questions???

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