TCP Simulation Evaluations over Ad Hoc Wireless Networks(3)

Number of Retransmissions Retransmissions vs. Paket Size (1 flows / 5%) 120NewReno Sack NewReno DASack DA 80 40 0 0 200 400 600 800 1000 1200 1400 1600

Paket Size (bytes)

(a)1 ow2hops

Number of Retransmission Retransmissions vs. Paket Size (1 flows / 5%) 120NewReno Sack NewReno DASack DA 80 40 0 0 200 400 600 800 1000 1200 1400 1600

Paket Size (bytes)

(b)1 ows5hops

Fig.7.Numberofretransmissionsfor1 owwithpacketerrorrateof5%

Figs.7and8showthatitisnotalwayspossibletogetthebestresultswithDAoption.OnceagaintheresultsdonotallowustomakecleardistinctionbetweenTCPNewrenoandTCPSACK avors.ItwasexpectedthatTCPSACKwouldperformbetterunderlosses,

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

mainlyforlargepacketsizes,sinceitsreceiverprovidesbetterinformationtothesenderaboutlosses.ThatwasobservedforthelargestpacketsizeinFigs.7,8,8(a)butnotinFig.8(b).However,thistendencywasnotobservedforthesmallerpacketsizes.

Retransmissions vs. Paket Size (10 flows / 5% )

900NewReno 800Sack NewReno DA 700Sack DA 600

500

400

300

200

100

0 0 200 400 600 800 1000 1200 1400 1600

Paket Size (bytes)Number of Retransmissions

(a)10 ows2hops

Number of Retransmission Retransmissions vs. Paket Size (10 flows / 5% ) 800NewReno 700Sack NewReno DA 600Sack DA 500 400 300 200 100 0 0 200 400 600 800 1000 1200 1400 1600

Paket Size (bytes)

(b)10 ows5hops

Fig.8.Aggregatenumberofretransmissionsfor10 owswithpacketerrorrate5%

E.Throughput

Inthissection,weinvestigatethebandwidthutilisationnotonlywithdifferentnumberofhopsbutalsodifferentnumberofconcurrent owsinthechaintopologyofFig.2.The

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

resultsareshowninFig.9,whichincludestheresultsfor1,10 owsandusingornottheDAoption.Itiswellknownthatthethroughputdecreasesasthenumberofhopsgohigh.Theprimaryreasonisthatthelongerthepaththehigherdelayforthepacketstoarriveatthedestination.Additionally,thereisthehiddennodeproblemthatbecomesworseforlargernumberofhops.So,theprobabilityofpacketlossissigni cantlyhigherforlargenumberofhopes.More ows,ontheotherside,meansmorecongestionwhichwilldecreasethethroughputaswell.

Throughput vs. Number of hops (1 flow)Throughput (kbits/s) 1600 1400 1200 1000 800 600 400 200

0 0 1 2 3 4 5 6

Number of hops 7 8NewReno Sack NewReno DASack DA

(a)1 ow

Throughput (kbits/s) Throughput vs. Number of hops (10 flows) 1600NewReno 1400Sack NewReno DA 1200Sack DA 1000 800 600 400 200

0 0 1 2 3 4 5 6

Number of hops 7 8

(b)10 ows

Fig.9.End-to-endthroughput

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

Fig.9(b)showsthattheaggregatethroughput,whichisthecapacityofthenetwork,isnearlythesameofthatobtainedinFig.9(a)inwhichonlyone owiscrossingthenetwork.Thedifferencebetweenthetwo avors,usingornotDA,istoosmalltoseefromthe gures.Onceagain,theDAoptionprovidedbetterresultforboth avors.Fig.9showsimprove-mentofupto7%,whichisnotverysigni cant.AmongtheTCP avorsthedifferenceiscompletelynegligible.

VI.CONCLUSIONS

Inthiswork,wehaveinvestigatedtheperformanceofTCPNewrenoandTCPSACKoveradhocnetworks.ns2wasusedforsimulatingthedifferentscenarios.Weusedthreemetrics:energyconsumption,throughputandretransmissionswithorwithoutdelayedacknowledgmentoptionDA.Weobservedthefollowing:

Theenergyconsumedatthesenderwasinverseleyproportionaltothepacketsizeregardlessofthe avor.

Theenergyconsumptionincreasedwithlossesforboth avorsaswell.

Thelossesincreasedtheretransmissionsnumberinallcases.

ThetwoTCP avorswithDAoptionspentingenerallessenergyandachievedbetterthroughputinmanycases.However,theDAoptiondidnotguaranteethebestresultinallcircumstances.

ThedifferencebetweentheTCP avorsperformancesweremoreperceptiveinthesimulationswithlosses.

TCPSACKperformedslightlybetterthanTCPNewrenoforlargepacketsizes.

Becauseofthelackoftime,weevaluatedonlyTCPNewrenoandTCPSACKprotocolswithorwithoutDAoption.IngeneraltheresultsdidnotshowusmeaningfuldifferencesbetweenthetwoTCP avors.AlthoughTCPSACKusestheselectiveacknowledgmentstrategy,itdidnotoutperformedTCPNewrenoinmostcasesasexpected.Therefore,thegeneraloutcomeisthatthetwo avorsworkquitethesameintheevaluatedscenarios,anddelayedacknowledgmentisindeedhelpfulinadhocnetworkswithouthighlevelofbiterrors.Forfuturework,moresimulationrunsanddifferentscenarioswithothermetricscouldbeconsidered.

REFERENCES

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