P2P视频点播系统外文翻译文献.docx

P2P视频点播系统外文翻译文献.docx

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P2P视频点播系统外文翻译文献

P2P视频点播系统外文翻译文献

（文档含中英文对照即英文原文和中文翻译）

原文：

RecentAdvancesinPeer-to-PeerMediaStreamingSystems

ABSTRACT

Recently,thereisgreatinterestinusingthepeer-to-peer（P2P）networkinmediastreaming.AgreatnumberofP2Pmediastreamingsystemshavebeendeveloped.Inthispaper,wefirstgiveabriefsurveyonsomekeytechniquesandalgorithmsinthefieldofP2Pstreamingresearch.WealsoanalyzethemarketviewofP2Pstreamingmediaservice,andgiveabriefdescrip-tionaboutthecurrentmainstreamP2PstreamingsystemsdeployedinChina.

I.INTRODUCTION

TherapiddevelopmentoftheInternethaschangedtheconven-tionalwaysthatpeopleaccessandconsumeinformation.Besidessendingandreceivinge-mails,browsingwebpages,anddownloadingdatafiles,peoplealsohopetocalltelephone,watchmovieandTV,andconductotherentertainmentsviathesameInternet.Theidealobjectiveisthatanyonecanaccessanything（contents）fromanywhereatanytime.ItiscommonlyconceivedthatthenextgenerationInternetshouldbeamulti-mediacommunicationnetworkbasedonthecoreofIPprotocol.Besidestraditionaldataservices,othermultimediacontentssuchasvoice,image,andvideo,wouldalsobedeliveredoverthesameIPnetwork,amongwhichthestreamingmediaservicewillplayaverymoreimportantrole.

Streamingmediaenablesreal-timeandcontinuousdeliveryofvideoandaudiodatainafashionof“flow”,i.e.,oncethesenderbeginstotransmit,thereceivercanstartplaybackalmostatthesametimewhileitisreceivingmediadatafromthesender,insteadofwaitingfortheentiremediafiletobereadyinthelocalstorage.Unlikenormaldatafile,astreamingmediafileishuge,thusrequireshighchannelbandwidth.Moreover,streamingmediaalsocarriesstringentdemandinthetimingofpacketdelivery.Thelargesizeofthestreamingmediaaswellasitsdeliverytimingrequirementcausesastreamingmediaservertobeexpensivetosetupandrun.Intraditionalclient/server-basedmediastreamingsystems,allclientsaccessthesameserverresource.Inthisscenario,ontheonehand,theprocessingpower,storagecapacity,andI/Othroughputoftheservermaybecomethebottleneck;ontheotherhand,largenumberoflong-distancenetworkconnectionsmayalsoleadtotrafficcongestion,thuscannotaffordbetterqualityofservice（QoS）comparablewiththatofothertradi-tionalInternetservices,suchasWWWandFTP,andcannotmeettheperformancerequirementsoflarge-scalereal-timemediastreamingapplications,especiallyintheaspectsofscalability,adaptability,fault-toleranceandrobustness.Toaddresstheseproblems,recentlyresearchershavepro-posedmanysolutions,suchasIPmulticastandCDN（contentdeliverynetwork）.However,bothofthemneedsupportsfromspecialhardware.ForIPmulticastnetwork,large-scalemulticast-capableroutersmustberedeployedintheInternet.Forcontentdeliverynetwork,alargenumberofCDNserversshouldbeplacedatthenetworkedge,closetoanyreceiver,andcooperatewitheachothertodistributemultimediadata.Thecostsofinfrastructuresetupandadministrationareexpensive,andcannotresolvetheproblemsfundamentally.Inrecentyears,Peer-to-Peer（P2P）networkingtechnologyhasgainedtremendousattentionfrombothacademyandindustry.InaP2Psystem,peerscommunicatedirectlywitheachotherforthesharingandexchangeofdataaswellasotherresourcessuchasstorageandCPUcapacity,eachpeeractsbothasaclientwhoconsumesresourcesfromotherpeers,andalsoasaserverwhoprovidesserviceforothers.P2Psystemscanbenefitfromtheirfollowingcharacteristics:

adaptation,self-organization,load-balancing,fault-tolerance,availabilitythroughmassivereplication,andtheabilitytopooltogetherandharnesslargeamountsofresources.Forexample,file-sharingP2Psystemsdistributethemaincostofsharingdata-bandwidthandstorage-acrossallthepeersinthenetwork,therebyallowingthemtoscalewithouttheneedforpowerfulandexpensiveservers.P2Psystemsareoriginallyappliedinnetworkfilesharing,andhaveachievedgreatsuccess,suchasNapster,Gnutella,Emule,andBitTorrent.However,differentfromgeneralP2Pfilesharing,P2Pmediastreamingposesmorestringenttimingandresourcerequirementsforreal-timemediadatatransmis-sionandrendering,thereforeitisneededtoprovidemorerestrictedfunctionsintherespectsofresourcemanagement,scheduling,andcontrol.

VariousP2Pmediastreamingsystemshavebeenproposedanddevelopedrecently.EveninChina,nowadaysthereareaboutmorethanadozenofP2Pstreamingapplicationsde-ployedintheInternet.Inthispaper,wefirstgiveabriefsurveyonsomekeyresearchissuesandalgorithmsofP2Pstreamingsystems,andthenanalyzeandsummarizethecurrentstatusanddevelopmenttrendofP2PstreamingmarketinChina.

II.RESEARCHPROGRESSOFP2PMEDIASTREAMING

AsimpleandstraightforwardwayofP2Pstreamingimplemen-tationistousethetechniqueofapplication-layermulticast（ALM）.WithALM,allpeernodesareself-organizedintoalogicaloverlaytreeovertheexistingIPnetworkandthestream-ingdataaredistributedalongtheoverlaytree.Thecostofprovidingbandwidthissharedamongthepeernodes,reducingtheburdenofthemediaserver.Inapplication-layermulticast,datapacketsarereplicatedandforwardedatendhosts,insteadofatroutersinsidethenetwork.ComparedwithIPmulticast,application-layermulticasthasseveraladvantages.Ontheonehand,sincethereisnoneedforsupportsfromrouters,itcanbedeployedgraduallybasedonthecurrentInternetinfrastructure;ontheotherhand,application-layermulticastismoreflexiblethanIPmulticast,andcanadaptdifferentdistributiondemandsofvariousupperlevelapplications.

Thus,howtoconstructandmaintainanefficientALM-basedoverlaynetworkhasbecameoneofthekeyproblemsofP2Pstreamingresearch.Toaddressthisproblem,mainlythreequestionsshouldbeanswered.ThefirstrelatestotheP2Pnetworkarchitecture,i.e.,whattopologiesshouldtheoverlaynetworkbeconstructed?

Thesecondconcernsroutingandschedulingofmediadata,i.e.,oncetheoverlaytopologyisdetermined,howtofindandselectappropriateupstreampeersfromwhichthecurrentpeerreceivestheneededmediadata?

Thethirdismembershipmanagement,i.e.,howtomanageandadapttheunpredictablebehaviorsofpeerjoininganddeparture?

Recently,severalP2Pstreamingsystemsandalgorithmshavebeenproposedtoaddresstheaboveissues.Fromtheviewofnetworktopology,currentsystemscanbeclassifiedintothreecategoriesapproximately:

tree-basedtopology,forest-based（multi-tree）topology,andmeshtopology.InthefollowingwegiveabriefsummarizationofP2Pstreamingtechniquesaccord-ingtothisclassification.

2.1Tree-basedtopology

Thetypicalmodeloftree-basedP2PstreamingsystemisPeerCast.InPeerCast,nodesareorganizedasasinglemulticasttree,wheretheparentprovideserviceonlydirectlytoitssons.

ThenodejoininganddeparturestrategiesusedinPeerCastaresimple.Fornodejoining,anewnodenfirstrequestservicesfromtherootnodeS.IftheShasenoughresources,itprovidesserviceforndirectly;otherwise,Sredirectstherequestofntooneofitssons.Thesonthenrepeatsthisprocess,untiltheparentofnisfound.Sinceeachnodeonlymaintainstheinformationofitsparentandsons,unbalancedtreemaybeconstructed.

Generally,thereexistfourrouteselectionstrategiesinPeerCast:

randomselection,round-robinselection,smartselectionaccord-ingtophysicalplacement,andsmartselectionaccordingtobandwidth.Toachieveabalancedmulticasttree,customroutingpolicyshouldbechosencarefullyforindividualpeernode.

ZIGZAGisanothertree-basedP2Pstreamingsystemwhichcanconstructmorebalancedmulticasttree.ZIGZAGorganizesreceiversintoahierarchyofbounded-sizeclustersandbuildsthemulticasttreebasedonthat.Theconnectivityofthistreeisenforcedbyasetofrules,whichguaranteesthatthetreealwayshasaheighOandanodedegreeO（k）,whereNisthenumberofreceiversandkisaconstant.Furthermore,theeffectsofnetworkdynamicssuchasunpredictablereceiverbehaviorsarehandledgracefullywithoutviolatingtherules.Thisisachievedrequiringaworst-casecontroloverheadofOreceiverandO（k）foranaveragereceiver.

Othertree-basedP2PstreamingsystemsalsoincludeNICE,Overcast,andBayeux.

2.2Forest-basedtopology

Conventionaltree-basedmulticastisinherentlynotwellmatchedtoacooperativeenvironment.Thereasonisthatinanymulticasttree,theburdenofduplicatingandforwardingmulticasttrafficiscarriedbythesmallsubsetofthepeersthatareinteriornodesinthetree.Mostofthepeersareleafnodesandcontributenoresources.Thisconflictswiththeexpectationthatallpeersshouldsharetheforwardingload.

Toaddressthisproblem,forest-basedarchitectureisbeneficial,whichconstructsaforestofmulticasttreesthatdistributestheforwardingloadsubjecttothebandwidthcon-straintsoftheparticipatingnodesinadecentralized,scalable,efficientandself-organizingmanner.Atypicalmodelofforest-basedP2PstreamingsystemisSplitStream.ThekeyideaofSplitStreamistosplittheoriginalmediadataintoseveralstripes,andmulticasteachstripeusingaseparatetree.Peersjoinasmanytreesastherearestripestheywishtoreceiveandtheyspecifyanupperboundonthenumberofstripesthattheyarewillingtoforward.Thechallengeistoconstructthisforestofmulticasttreessuchthataninteriornodeinonetreeisaleafnodeinalltheremainingt