TCP Simulation Evaluations over Ad Hoc Wireless Networks

The Transmission Control Protocol (TCP) represents the most deployed transport protocol used in the Internet so far. This popularity motivates its presence in wireless networks, including ad hoc networks. These networks are very promising since they make i

UniversityofBern&

NCCRMICSSummerInternship2004

TCPSimulationEvaluationsoverAdHocWirelessNetworks

Student:DermanAkcelikSupervisor:RuydeOliveiraProfessor:TorstenBraundakcelik@eivd.ch

The Transmission Control Protocol (TCP) represents the most deployed transport protocol used in the Internet so far. This popularity motivates its presence in wireless networks, including ad hoc networks. These networks are very promising since they make i

The Transmission Control Protocol (TCP) represents the most deployed transport protocol used in the Internet so far. This popularity motivates its presence in wireless networks, including ad hoc networks. These networks are very promising since they make i

TCPSimulationEvaluationsoverAdHocWirelessNetworks

Abstract

TheTransmissionControlProtocol(TCP)representsthemostdeployedtransportprotocolusedintheInternetsofar.Thispopularitymotivatesitspresenceinwirelessnetworks,includingadhocnetworks.Thesenetworksareverypromisingsincetheymakeitpossiblecommunicationamongendsystemsdirectlywithoutanyinfrastructure.However,TCPfacesvariousproblemswhenrequiredtoworkinsuchenvironments.Becauseofthat,itisveryimportanttounderstandthebehaviourofthisprotocolinwirelessnetworks.ThisprojectevaluatesTCPperformanceinadhocnetworksbymeansofsimulation.WecomparetwoTCP avours,namelyNewrenoandSACK,underavarietyofconditions.Speci cally,weassessedthroughput,retransmissions,andenergyconsumptionfeaturesofTCP.WealsoevaluatedthedelayedacknowledgmentoptionforTCP.Theresultsprovidedsomeinsightintothisquitewidesubject.

The Transmission Control Protocol (TCP) represents the most deployed transport protocol used in the Internet so far. This popularity motivates its presence in wireless networks, including ad hoc networks. These networks are very promising since they make i

I.INTRODUCTION

Intoday’sworld,wirelessdevicesbecameanevidentpartofourlife.Thesedevicesmayprovideseamlessconnectivityinenvironmentswherewirednetworksarenotpossibleordesirable.Oneoftheemergingwirelesstechnologiesisadhocnetworks.Thesenetworksareattractivefornotdependingonany xedinfrastructuretocommunicate.Asaresult,researchesonadhocwirelessnetworkshavegainednon-negligiblepopularityinrecentyears.Adhocnetworksconsistofmobilehoststhatcommunicatewitheachotheroverawirelessmediumwithoutcentralcontrol.Theutilisationofthismediumdevelopsthehidden-nodeproblemandexposednodeproblemsthatareinvestigatedinmoredetailin[1].Inanadhocnetwork,thetopologymaychangeduetovariousmediumconstraints,forcingself-reconstructionadaptness.Becauseofthedistancelimit,multihoproutingisusedwherethepacketsareforwardedtowardsthenextnodealongaroutetothereceiver.Energyconsumptionisalsoaconcerninthesenetworksbecausethenodesaresupposedtobebatterypowered.TheIEEEproposedIEEE802.11asastandardMACprotocolforwirelessmultihopnetworks[2].Itde nesthelinkandphysicallayerspeci cations.ItminimizestheknownhiddennodeproblemusingalocalretransmissionstrategywithRTS/CTS(request-to-send/cleartosend)controlframes.Itworksef cientlyforscenarioshavingatmost3hops.Therefore,end-to-endcommunicationprotocolshavetodealwiththeproblemforthebestuseofnetworkbandwidth.ThepopularityoftheTCPintheInternetmotivatesitspresenceonthewirelessnetworks.SinceTCPwasdevelopedforwiredenvironments,ithasdistinctbehaviorinadhocnetworks.Inthesenetworks,TCPwillseeeverydroppedpacketasacongestionsign.Itwillreduceitssendingrate,whichmeanslessthroughput,moreretransmissionsandmorespentenergy.Packeterrorrateofthewirelesschannelsandlinkinterruptionsareotherreasonsforpacketlosses.TheinteractionbetweenTCPandtheIEEE802.11MACprotocolisoneofthemostchallengingtopicsintoday’swirelesscommunicationsystems.TCPNewrenoandTCPSACKaretwoimportant avorsofTCPprotocol.Theirfeaturesarequitedistinctthough.TCPNewrenousesanewfastrecoverymechanismforspeedinguptherecoveryfromlosses.TCPSACKhasareceiverthatgivesmoreinformationaboutthelostpacketstothesender.AsenderofTCPSACKusesthisfeatureforrecoveringquicklyinsituationinwhichmultiplepacketlosseswithinasinglewindowoccur.TCPSACKclaimtobeverygoodtodealwithapacketlossbecauseofitsselectiveacknowledgementstrategy.Nevertheless,addingextrainformationtobesentimplymorespentenergy.BothTCP avorsmayworkwiththedelayedacknowledgement(DA)option,whichmeansthatthereceiveracknowledgesonlyonepacketoutoftwotworeceived.Thisisexpectedtoreduceenergyconsumption.Theaimofthisworkistocharacterize,energyconsumption,numberofretransmissionsandthroughputforTCPNewrenoandTCPSACK avors,withandwithoutDelayedAcknowledgement(DA).Becauseofthetimelimit,wefocusedonthesetwotopical avors.Additionally,wedonotaddressmobilityrelatedissues,sincethegoalhereistoevaluatethebehaviorofTCPovertheIEEE802.11MACprotocol.

The Transmission Control Protocol (TCP) represents the most deployed transport protocol used in the Internet so far. This popularity motivates its presence in wireless networks, including ad hoc networks. These networks are very promising since they make i

Theremainderofthisreportisorganizedasfollows.SectionIIgivesgeneralinformationaboutadhocnetworks.SectionIIIdescribestheconceptsthatlearntbythestudentduringthisstudy.SectionIVpresentsthesimulationenvironmentsandthesimulatedscenarios.SectionVcontainsthesimulationresultsandtheirdiscussions.Finally,sectionVIsumma-rizesourwork.

II.ADHOC

Anad-hocnetworkisalocalareanetworkorothersmallnetworkthatisnotdependentonanyaccesspointoranyserver.Fig.1showsatypicaladhocnetworkthatcommunicatesoverawirelessmedium.Asthenodesaremobileitstopologymaychangecontinuously.Thedevicescanjoinandleavenetworksreadily.Eachdeviceisimmediatelyrecognizedaspartofthenetworkwheniscloseenoughtooneofthenetwork

components.Fig.1.Adhocnetworks

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