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End-to-End Available Bandwidth Estimation Tools, an Experimental Comparison

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End-to-EndAvailableBandwidthEstimation

Tools,anExperimentalComparison

EmanueleGoldoni1andMarcoSchivi2

1UniversityofPavia,Dept.ofElectronics,27100-Pavia,Italyemanuele.goldoni@unipv.it2UniversityofPavia,Dept.ofComputerEngineeringandSystemsScience,27100-Pavia,Italymarco.schivi01@ateneopv.it

Abstract.Theavailablebandwidthofanetworkpathimpactstheper-formanceofmanyapplications,suchasVoIPcalls,videostreamingandP2Pcontentdistributionsystems.Severaltoolsforbandwidthestimationhavebeenproposedinthelastyearsbutthereisstilluncertaintyintheiraccuracyandefficiencyunderdifferentnetworkconditions.Althoughanumberofexperimentalevaluationshavebeencarriedoutinordertocomparesomeofthesemethods,acomprehensiveevaluationofalltheexistingactivetoolsforavailablebandwidthestimationisstillmissing.Thisarticleintroducesanempiricalcomparisonofmostoftheactiveesti-mationtoolsactuallyimplementedandfreelyavailablenowadays.Abing,ASSOLO,DietTopp,IGI,pathChirp,Pathload,PTR,SpruceandYazhavebeencomparedinacontrolledenvironmentandinpresenceofdif-ferentsourcesofcross-traffic.Theperformanceofeachtoolhasbeeninvestigatedintermsofaccuracy,timeandtrafficinjectedintothenet-worktoperformanestimation.

1Introduction

Availablebandwidthisafundamentalmetricfordescribingtheperformanceof

anetworkpath.Thisparameterisusedinmanyapplications,fromroutingalgo-

rithmstocongestioncontrolmechanismsandmultimediaservices.Forexample,

in[1,2]theauthorsinvestigatedtheimportanceoftheavailablebandwidthfor

adaptivecontentdeliveryinpeer-to-peer(P2P)orvideostreamingsystems.

Theeasiestandmosteffectivemethodforestimatingtheavailablebandwidth

isactiveprobing–afewtestpacketsaretransmittedthroughthepathand

areusedtoinferthenetworkstatus.Theproblemofend-to-endestimation

hasreceivedconsiderableattentionandanumberofactiveprobingtoolshave

emergedinrecentyears[3].Nevertheless,producingreliableestimationsstill

remainschallenging:themeasurementprocessshouldbeaccurate,non-intrusive

androbustatthesametime.

Considerableeffortshavealsobeenputincomparisonprojectsaimingto

analyzetheperformancesofexistingmethodsindifferentnetworkscenarios.http://www.wdklife.com 五道口生活网 http://www.wdklife.com/bbs 五道论坛http://www.wdklife.com 五道口生活网 http://www.wdklife.com/bbs 五道论坛

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Nevertheless,manyissuesremainstillunresolvedandthequestforthebest

availablebandwidthestimationtoolisstillopen[4].

Comparedtopreviousworks,thispaperproposesthelargestcomparisonof

availablebandwidthestimationmethods.Theperformancesof9differenttools

areinvestigatedintermsofaccuracy,timeandintrusiveness.Alltheexperiments

havebeenconductedinalow-costandflexibletestbedwhichcouldbeeasily

extendedtosimulatemorecomplexandrealisticnetworktopologies.

Theremainderofthearticleisorganizedasfollows.Section2brieflypresents

relatedworksonmeasurementtoolsandpastperformancecomparisons.InSec-

tion3wedescribethetestbedandthemethodologyadoptedfortheexperi-

mentalcomparisonofthetools.Next,Section4includesthepreliminaryresults

obtainedduringtheperformancetestsweperformedinourlaboratory.Finally,

theconclusionsdrawnfromthisstudyarepresentedinSection5.

2BackgroundandRelatedWork

Manysoftwaretoolsfornetworkbandwidthmonitoringhavebeendevelopedin

thelastyearsbybothindependentscientistsandcollaborativeresearchprojects.

Althoughdesignedforthesamepurpose,thesetoolsarebasedondifferentprin-

ciplesandimplementvarioustechniques.Thissectionbrieflyintroducesthemain

methodologiesproposedinliteratureandalsodescribesthepreviousworkscar-

riedouttocomparethem.

2.1MeasurementTechniques

Severalactiveend-to-endmeasurementtoolshavebeenproposedinthelast

years.Lookingatthebigpicture,thesesystemsinfertheavailablebandwidthof

anetworkpathbysendingafewpacketsandanalyzingtheeffectsontheprobe

framesofintermediatenodesandcross-traffic.

ExamplesofprobingtoolswhichhaveemergedinrecentyearsarePathload

[5],IGI/PTR[6],Abing[7],Spruce[8],pathChirp[9],DietTopp[10],Yaz[11],

andASSOLO[12].Thesemethodsdifferinthesizeandtemporalstructure

ofprobestreams,andinthewaytheavailablebandwidthisderivedfromthe

receivedpackets.

Spruce[8]usestensofpacketpairshavinganinputratechosentoberoughly

aroundtothecapacityofthepath,whichisassumedtobeknown.Moreover,

packetsarespacedwithexponentialintervalsinordertoemulateapoissonian

samplingprocess.

IGI[6]usesasequenceofabout60unevenlyspacedpacketstoprobethe

networkandthegapbetweentwoconsecutivepacketsisincreaseduntilthe

averageoutputandinitialgapsmatch.Similarly,PTRreliesonunevenlyspaced

packetsbutthebackgroundtrafficisdetectedthroughacomparisonofthetime

intervalsatthesourcewiththosefoundonthedestinationside.

Abing[7]reliesonpacketpairdispersiontechnique.Typically,10or20closely

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课后习题及答案

课后习题及答案

第一章

1. (Q1) What is the difference between a host and an end system? List the types

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BPSK-R信号与BOC信号码跟踪性能分析及比较

BPSK-R信号与BOC信号码跟踪性能分析及比较

BPSK-R信号与BOC信号码跟踪性能分析及比较

何在民;胡永辉;武建锋;马红皎;王继刚;王康

【摘 要】分析了射频前端带宽与BOC信号自相关函数的关系,研究了射频前端带宽和早迟码间距对S曲线的影响。在规范的TOA误差估计模型框架下,采用非相干延时码跟踪锁定环,推导出非相干延时锁定环理论计算的码跟踪误差与射频前端带宽、早迟码间距、载噪比、积分时间和码环路带宽之间的关系表达式,从而定量地分析了非相干延时锁定环的码跟踪误差。最后对BPSK-R信号和BOC（10,5）信号的码跟踪性能做了比较,比较表明,BOC（10,5）信号的码跟踪性能优于传统的BPSK-R信号,在相同的码跟踪精度条件下,BOC（10,5）比10.23 MHz BPSK-R信号所需要的载噪比约低7 dB,比1.023 MHz BPSK-R信号低15 dB左右。%The

relationship between the autocorrelation function of BOC signal and the

radio-frequency front-end bandwidth is analyzed,and the influence of

radio-frequency front-end bandwidth and spacing between early code and

late code on the S curve is studied.Under the canonical model framework

of TOA error estimation and with the no-coherent delay lock loop,a

quantitative formula which relates the theoretically calculated code

tracking error to the RF front-end bandwidth,spacing between early code