視頻媒體外文翻譯文獻(xiàn)

視頻媒體外文翻譯文獻(xiàn)視頻媒體外文翻譯文獻(xiàn)(文檔含英文原文和中文翻譯)原文：RecentAdvancesinPeer-to-PeerMediaStreamingSystemsABSTRACTRecently,thereisgreatinterestinusingthepeer-to-peer(P2P)networkinmediastreaming.AgreatnumberofP2Pmediastreamingsystemshavebeendeveloped.Inthispaper,wefirstgiveabriefsurveyonsomekeytechniquesandalgorithmsinthefieldofP2Pstreamingresearch.WealsoanalyzethemarketviewofP2Pstreamingmediaservice,andgiveabriefdescrip-tionaboutthecurrentmainstreamP2PstreamingsystemsdeployedinChina.INTRODUCTIONTherapiddevelopmentoftheInternethaschangedtheconven-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.RESEARCHPROGRESSOFP2PMEDIASTREAMINGAsimpleandstraightforwardwayofP2Pstreamingimplemen-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-basedtopologyThetypicalmodeloftree-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-basedtopologyConventionaltree-basedmulticastisinherentlynotwellmatchedtoacooperativeenvironment.Thereasonisthatinanymulticasttree,theburdenofduplicatingandforwardingmulticasttrafficiscarriedbythesmallsubsetofthepeersthatareinteriornodesinthetree.Mostofthepeersareleafnodesandcontributenoresources.Thisconflictswiththeexpectationthatallpeersshouldsharetheforwardingload.Toaddressthisproblem,forest-basedarchitectureisbeneficial,whichconstructsaforestofmulticasttreesthatdistributestheforwardingloadsubjecttothebandwidthcon-straintsoftheparticipatingnodesinadecentralized,scalable,efficientandself-organizingmanner.Atypicalmodelofforest-basedP2PstreamingsystemisSplitStream.ThekeyideaofSplitStreamistosplittheoriginalmediadataintoseveralstripes,andmulticasteachstripeusingaseparatetree.Peersjoinasmanytreesastherearestripestheywishtoreceiveandtheyspecifyanupperboundonthenumberofstripesthattheyarewillingtoforward.Thechallengeistoconstructthisforestofmulticasttreessuchthataninteriornodeinonetreeisaleafnodeinalltheremainingtreesandthebandwidthconstraintsspeci-fiedbythenodesaresatisfied.Thisensuresthattheforwardingloadcanbespreadacrossallparticipatingpeers.Forexample,ifallnodeswishtoreceivekstripesandtheyarewillingtoforwardkstripes,SplitStreamwillconstructaforestsuchthattheforwardingloadisevenlybalancedacrossallnodeswhileachievinglowdelayandlinkstressacrossthesystem.Stripingacrossmultipletreesalsoincreasestheresiliencetonodefailures.SplitStreamoffersimprovedrobustnesstonodefailureandsuddennodedepartureslikeothersystemsthatexploitpathdiversityinoverlays.SplitStreamensuresthatthevastmajorityofnodesareinteriornodesinonlyonetree.Therefore,thefailureofasinglenodecausesthetemporarylossofatmostoneofthestripes(onaverage).Withappropriatedataencodings,applicationscanmaskormitigatetheeffectsofnodefailuresevenwhiletheaffectedtreeisbeingrepaired.BesidesSplitStream,therearemanyotherforest-basedsystems.Examplesincludebuildingmesh-basedtree(Naradaanditsextensions,andBullet),leveraginglayeredcoding(PALS),andmultipledescriptioncoding(CoopNet).2.3MeshtopologyInconventionaltree-basedP2Pstreamingarchitectures,atthesametimeapeercanonlyreceivedatafromasingleupstreamsender.Duetothedynamicsandheterogeneityofnetworkbandwidths,asinglepeersendermaynotbeabletocontributefullstreamingbandwidthtoapeerreceiver.Thismaycauseseriousperformanceproblemsformediadecodingandrendering,sincethereceivedmediaframesinsomeendusersmaybeincomplete.Inforest-basedsystems,eachpeercanjoinmanydifferentmulticasttrees,andreceivedatafromdifferentupstreamsenders.However,foragivenstripeofamediastream,apeercanonlyreceivethedataofthisstripefromasinglesender,thusresultsinthesameproblemlikethecaseofsingletree.Multi-senderschemeismoreefficienttoovercometheseproblems.Inthisscheme,atthesametimeapeercanselectandreceivedatafromadifferentsetofsenders,eachcontributingaportionofthestreamingbandwidth.Inaddition,differentfromthemulti-treesystems,thesendersetmembersmaychangedynamically,duetotheirunpredictableonline/offlinestatuschanges,andthetime-variablebandwidthandpacket-lossrateoftheInternet.Sincethedataflowhasnotafixedpattern,everypeercansendandalsoreceivedatafromeachother,thusthetopologyofdataplanelikesmesh.Themainchallengesofmeshtopologyarehowtoselectthepropersetofsendersandhowtocooperateandschedulethedatasendingofdifferentsenders.Examplesofmesh-basedmulti-senderP2PstreamingsystemincludeCollectCast,GnuStream,andDONet(CoolStreaming).CollectCastputsitsemphasismainlyonthejudiciousselec-tionofsenders,constantmonitoringofsender/networkstatus,andtimelyswitchingofsenderswhenthesenderornetworkfailsorseriouslydegrades.CollectCastoperatesentirelyattheappli-cationlevelbutinfersandexploitsproperties(topologyandperformance)oftheunderlyingnetwork.EachCollectCastsessioninvolvestwosetsofsenders:thestandbysendersandtheactivesenders.Membersofthetwosetsmaychangedynamicallyduringthesession.ThemajorpropertiesofCollectCastincludethefollowing:(1)itinfersandleveragestheunderlyingnetworktopologyandperformanceinformationfortheselectionofsenders.Thisisbasedonanovelapplicationofseveralnetworkperformanceinferencetechniques;(2)itmonitorsthestatusofpeersandconnectionsandreactstopeer/connectionfailureordegradationwithlowoverhead;(3)itdynamicallyswitchesactivesendersandstandbysenders,sothatthecollectivenetworkperformanceoutoftheactivesendersremainssatisfactory.GnuStreamisareceiver-drivenP2PstreamingsystemwhichisbuiltontopofGnutella.Itfeaturesmulti-senderbandwidthaggregation,adaptivebuffercontrol,peerfailureordegradationdetectionandstreamingqualitymaintenance.GnuStreamisawareofthedynamicsandheterogeneityofP2Pnetworks,andleveragestheaggregatedstreamingcapacityofindividualpeersenderstoachievefullstreamingquality.GnuStreamalsoper-formsself-monitoringandadjustmentinthepresenceofpeerfailureandbandwidthdegradation.Recently,DONetimplementedamulti-sendermodelbyintroducingasimplerandstraightforwarddata-drivendesign,whichdoesnotmaintainanevenmorecomplexstructure.ThecoreofDONetisthedata-centricdesignofstreamingoverlay,andtheGossip-baseddatascheduleanddistributionalgorithm.Inthedata-centricdesignofDONet,anodealwaysforwardsdatatoothersthatareexpectingthedata,withnoprescribedroleslikefather/child,internal/external,andupstreaming/downstreaming,etc.Inotherwords,itistheavailabilityofdatathatguidestheflowdirections,whilenotaspecificoverlaystructurethatrestrictstheflowdirections.Thisdata-centricdesignissuitableforoverlaywithhighdynamicnodes.GossipalgorithmshaverecentlybecomepopularsolutionstomulticastmessagedisseminationinP2Psystems.Inatypicalgossipalgorithm,anodesendsanewlygeneratedmessagetoasetofrandomlyselectednodes;thesenodesdosimilarlyinthenextround,andsodoothernodesuntilthemessageisspreadtoall.Therandomchoiceofgossiptargetsachievesresiliencetorandomfailuresandenablesdecentral-izedoperations.Similartotherelatedwork,DONetemploysagossipingprotocolmembershipmanagement.Thedatasched-uleanddistributionmethodusedinDONetisalsopartiallymotivatedbythegossipconcept.Itusesasmartpartnerselectionalgorithmandalow-overheadschedulingalgorithmtointelligentlypulldatafrommultiplepartners,whichgreatlyreducesredundancy.Experimentsshowthat,comparedwithatree-basedoverlay,DONetcanachievemuchmorecontinuousstreamingwithcomparabledelay.III.P2PSTREAMINGINCHINASincethefirstpracticalP2Pstreamingmediasystemwasborn,P2PstreamingservicehasexperiencedasignificantgrowthinChina,especiallyintheyear2005and2006.Accordingtoamarketreport,overmorethan12,000,000InternetusershaveaccessedP2PstreamingserviceordownloadedP2PstreamingsoftwareinChina.Itispredictedthatbytheendoftheyear2006,thisnumbercantakeagrowthtoabove25,000,000.Facingsuchalargepre-profitablemarket,tillnowthereareatleastover15organizationsthatareprovidingP2Porlikelystreamingservices.Withthemostrepresentative,PPlive,PPstream,Mysee,ROXandUUseehavetakenover80%ofthecurrentmarketshare.Intherestofthissection,wewillanalyzethemarketviewofP2Pstreamingmediaservice,andthengiveabriefintroductiontothecurrentmainstreamP2PmediastreamingsystemsdeployedinChina.TherearethreereasonswhichcauseP2PmediastreamingservicesopopularinChinainrecentyears.Firstly,thankstotherapidadvanceofaudioandvideocompressiontechnologies,userscaneasilyhaveaccesstostreamingmediainaverylowbitrate.Moreandmoremultimediaproductions,TVclips,andmoviesarefullofthewholeInternet.ThismakestheP2Pstreamingserviceproviderseasiertogetenoughmediasourcesforservicethanbefore.Withthevariousandabundantsupplyofmediacontents,serviceproviderscanattractmoreandmoreclients.Thelargertheclientnumber,theeasiertomaketestofsoftwareandservices.Secondly,comparedwiththetraditionalwayofwatchingvideofromtheInternet,suchasVOD,userscangetmoresatisfiedqualityofserviceincurrentbandwidth-limitednetworkenvironment.Finally,bythegrowthofusers’snetworkaccessbandwidth,theydemandonmoreluxuryexperience,notsimplyontextandpictures,butmoreonfluentandhigh-definitionvideos.Users’trendmakesalargeroomageforP2Pstreamingservicetogrow.AlthoughP2Pstreamingservicehasachievedaconsiderableuserexperienceanddefinitelyitwouldhaveabrightfuture,therearestillseveralissuesneedtopayattentionto.First,currentserviceprovidershavenotfoundanydistinctbusinessmodelsyet.Currently,almostallP2PsolutionvendorsareprovidingTVprogram/moviebroadcastingsfreeofcharge.Obviously,itisnotpracticalfortheserviceprovidertochargetheusersinthetimeofpromotingtheservice.Inthestartingperiod,developingusernumbersandgainingsubscribersarethekeypointsbutearningprofits.Second,P2Pstreamingserviceprovidersshouldfacethechallengeofcopyright.Aswe’vejustmentioned,someP2PvendorsprovideTV/moviebroadcastingusingthirdpartycontentswithoutcheckingtheirlegalstatus.Forlongtermdevelopment,serviceprovidersmustmakecooperationwithcontentproviderstomakeatwinwin.ThirdlyP2Pstreamingserviceprovidersmustfacethesur-veillancefromtheInternetserviceproviders(ISPs)andgovern-mentalauthorities.Ontheonehand,thepurposeofP2Pistomaximizetheusageofbandwidthresource,however,totheopposite,thebandwidthspewingcausedbysuchapplicationsoftenmakestheISPsfeelintolerable.ISPsusuallytakerejec-tiveactions,suchaslimitingtheapplicationbandwidthorevenblockingtheapplicationfromrunningontheInternet.However,limitingorblockingisnotthemostproperwaytosolvetheproblem,andtheconflictsbetweentheISPsandP2Pstreamingserviceproviderswillbeinexistenceforacertainwhile.Ontheotherhand,beingregardedasanewmediatrendontheweb,governmentalauthoritiesmusttakesurveillanceonP2Pstream-ingservicetoguaranteetheorderlinessoftheindustry.Bythetwosidesofsurveillance,P2Pstreamingserviceprovidersmustplaythegameprudentially.PP,investedbySoftBankHK,whichisacknowl-edgedasthenumberoneintermsofsubscribersinChina,wasfoundedintheearly2005.PPlivehasverystableplayingquality,anditseldomchangestheplayer’sstatetobufferingduringplaying.Whenwatchinganewchannel,theaveragewaitingtimefromsearchingtoplayingisabout35sto55s.PPliveprovidesover200channels,categorizedbyProvincialTVstations,Sports,Cartoon,Entertainment,HKfilms,Gaming,Moviesetc,butveryfewprogramsofoverseasTVstations.PPlivecurrentlyonlysupportsbroadcasting,andalmostalltheprogrambitrateisbetween300kbps~400kbpswithmediacodeclikeWindowsMediaVideo(.wmv)orRealMedia(.rm).Itsprogramtimetableisbothshownonthewebsiteanddisplayedattheclientplayer.Advertisingcommercialsissupportedbytheclient.Worthtobementioned,PPlivebroadcastedSupergirlContestsin2005anditwasreportedthattheconcurrentonlineusershitarecordof500kforthefinalcontest.Thoughthepopularusersithas,somecontentsPPliveprovidesarelackofcopyright,whichmaybeahiddentroubleforitslongtermdevelopment.PPstream,whichisfoundedbytwoengineersinSichuanProvince,wasannouncedalsointheyear2005.ComparedwithPPlive,PPstreamhassimilarfunctionsbuthigherconnectingspeed.Usuallywhenopeninganewchannel,theaveragewaitingtimeisabout25s~45s,anditswatchingfluencyisalsoasgoodasPPlive.PPstreamprovidesaround90channels,categorizedbyPhoenixTV,WenguangTV,Sports,Entertainment,Movie,TVdramaseries,Gaming&cartoon,Musicandradiochannel,andetc.PPstreamcurrentlybroadcastsWindowsMediaVideocodedQVGAandCIFqualityvideoswithbitratearound300kbps~440kbps.Itsclientsoftwaresupportschannellistandtimetableshownasidetheplayer,advertisingcommercialsarealsosupported.IthasbeenreportedthatPPstreamwillhavecooperationwithsomeISPsforhigherperformance,anditsmarketpolicyseemsmoresteadyandlong-ranged.Mysee,investedbyaurora,whichwasfoundedinlate2005,isregardedasalatercomer.ButMyseegrowsquicklyintheyear2006.Now,bynumbersofmediareports,itisveryfamousontheInternet.MyseesuppliesthesamevideocodeclikePPstream,butsometimestheconnectingspeedandplayingqualitymaynotbeasgoodasthatofPPstreamandPPlive.Itcurrentlybroadcastsaround90channelswhicharecategorizedbynews,movie,TVdramaseries,sports,entertainment,music,information,Cartoonandscience.Myseedoesnotprovideaclientapplicationplayertoviewprograms,allthechannelsareviewedintheMicrosoftIEbrowser,channellistandtimetablearebothdisplayedonitswebsite.Thiswaymaybeeasyfortheserviceprovidertoarrangecontentsthatrecommendedtotheuser,butlackofuserglutinosity.ItisreportedthatMyseehasnearoneyeargoodcooperationwithandHunanTVstationforvideobroadcasting.ItcanbepredictedthatwithpreponderanceincooperatingwithTVstationsandICPs,Myseewouldearnamoreconsiderablemarketshare.Roxbeam,usedtobecalledCoolStreaming,isregardedasthefirstpracticalP2Pstreamingsoftware.CoolStreamingwasdevel-opedinlate2004.ItgaveareliablemodelofP2Pstreaming.ButCoolStreamingwasforcedtoclosedownduetolawsuitsregardingthecontentinearly2005.CurrentlyRoxbeamissupportedbySoftBankJapan.ItnotonlysuppliesP2Pstreamingservice,butintegratesonlinecommunitycalledLeiKeandchattingservicesintotheclientsoftware.UserscanwatchnotonlybroadcastingprogrambutshortvideoclipsviatheVODservice.Roxbeamtriestoprovidevariousvideorecoursestoitsuser,anditsgoalisnotsimplyprovidingaP2Pstreamingservice,buttoprovideanonlinevideosharingandcommunicationplatform.Obviously,Roxbeamhasanevengranderblueprint,butwhetherthisblueprintcancometrueistobeprovedbythemarket.UUsee,whichisinvestedbySIG,formedinmid2005,isalsoanewpowerintheP2Pstreamingservice.HavinggoodrelationshipwithCCTV,UUseehasmorepreponderancethanothercompanionsonprogramcopyrights,whichcanhelpthemmuchinlivingbroadcastoflarge-scaleactivitiesandprograms.UUseeprovidesabout100channelsonitsclientplayerwhichiscategorizedbyUUseerecommendation,entertainment,sports,movies,TVdrama,fashion,cartoon,gaming,science,socialnews,civilTVstationsandetc,channellistandtimetableareshownfriendlyontheclientplayer.UUseealsoprovidesthousandsofVODprogramsonitswebsite,whichcaneffec-tivelyincreaseitsadhesiveabilitytotheusers.BythenewestdatacollectionfromACNielsen,duringthelivingbroadcastofCCTV’s2006SpringFestivalCelebration,theUUsee’susernumberatthepeaktimehasmettheamountof400,000,whichisthelargestnumberfromtheauthority’sreport.Bythedailyreachstatisticfrom(http://www.),intherecenthalfyear,UUseeandPPlivetakethefirsttwochairsinthecompetition,followedwithPPstreamandMysee,Roxbeamtakesthelast.ItcouldbejudgedthattheWorldCupinJuneandSuperGirlfromMaytoSeptembercontributemoreaudiencestotheServiceproviders.OtherP2PstreamingserviceproviderslikeQQLive,Pcast,TVants,Poco,51TVandsoonaredoingthesamecontributiontothismarket.Chanceisequaltoeverycompetitor,whethertheycanachievealldependsonthemarketchoice.IV.CONCLUSIONRecently,P2Pstreaminghasattractedalotofattentionsfrombothacademyandindustry.VariousP2Pmediastreamingalgorithmshavebeenstudied,andthesystemshavebeendeveloped.NowadaysaboutmorethanadozenofP2PstreamingsystemshavebeendeployedinChina.Inthispaper,wefirstgiveabriefsurveyontheprogressofP2Pstreamingresearch,bringforwardsomefundamentalproblemsforP2Pstreamingapplicationdevelopment,andreviewseveralsolu-tionseverproposedtoaddresstheproblems.Furthermore,westudythefactorswhichcanimpactthetrendsofP2Pstream-ingmarket,andmakeabriefsummaryforthecurrentP2PstreamingmarketprogressinChina.

譯文：P2P視頻點(diǎn)播系統(tǒng)的最新進(jìn)展高文，霍龍懾，付強(qiáng)摘要近年來，人們對(duì)使用P2P視頻點(diǎn)播系統(tǒng)越來越感興趣，并開發(fā)出了大量的P2P媒介瞬時(shí)系統(tǒng)。本文，我們首先對(duì)P2P點(diǎn)播技術(shù)研究領(lǐng)域的一些關(guān)鍵技術(shù)和運(yùn)算法則做了簡(jiǎn)單的調(diào)查，并對(duì)中國(guó)當(dāng)前的P2P視頻點(diǎn)播系統(tǒng)發(fā)展的主流做了簡(jiǎn)單的描述。簡(jiǎn)介快速發(fā)展的因特網(wǎng)已經(jīng)改變了人們獲取信息和利用信息的傳統(tǒng)方式。除收發(fā)電子郵件，瀏覽網(wǎng)頁，下載數(shù)據(jù)文件之外，人們也希望通過同樣的因特網(wǎng)打電話，看電影，看電視以及進(jìn)行其他的娛樂活動(dòng)。要達(dá)到的理想目標(biāo)是：任何人都能隨時(shí)隨地地獲取任何信息（內(nèi)容）。人們一般想像的下一代因特網(wǎng)是基于IP協(xié)議中心之上的多媒體通訊網(wǎng)絡(luò)。除了傳統(tǒng)的數(shù)據(jù)服務(wù)，其他的多媒體內(nèi)容，如聲音，影像以及視頻也可以通過同一IP網(wǎng)絡(luò)傳送，其中，瞬時(shí)媒介服務(wù)將會(huì)發(fā)揮更為重要的作用。點(diǎn)播媒體能使視頻和音頻的以一種“流動(dòng)”的方式進(jìn)行實(shí)時(shí)和不間斷的傳輸。例如：一旦發(fā)送方開始傳輸，接收方在接收媒介數(shù)據(jù)的同時(shí)可以重放，而不是等待整個(gè)媒體資料存儲(chǔ)到本地存儲(chǔ)后再播放。與普通數(shù)據(jù)文件不同的是，點(diǎn)播媒介文件非常大，因此需要高頻道帶寬。此外，點(diǎn)播媒介在文件包傳輸?shù)臅r(shí)間上也有嚴(yán)格的要求。流媒體的大規(guī)格和傳輸時(shí)間的要求使得點(diǎn)播媒體服務(wù)器的建立和運(yùn)行非常的昂貴。在傳統(tǒng)的以用戶∕服務(wù)器為基礎(chǔ)的媒體點(diǎn)播系統(tǒng)中，所有的用戶從同一服務(wù)器源頭獲取信息。在這種情況下，服務(wù)器的處理能力，存儲(chǔ)能力，輸入和輸出流量和成為瓶頸；另一方面，大量的遠(yuǎn)程網(wǎng)絡(luò)連接也會(huì)導(dǎo)致?lián)頂D。因此，與其他傳統(tǒng)因特網(wǎng)服務(wù)相比，如萬維網(wǎng)（WＷＷ）和文件傳輸協(xié)議（ＦＩＰ），就無法提供優(yōu)質(zhì)服務(wù)（ＱｏＳ），并且也無法滿足大規(guī)模流媒體的點(diǎn)播應(yīng)用的性能，特別是在延展性，適應(yīng)性，容錯(cuò)性和健全性方面的性能。為了解決這些問題，最近，研究人員提出了許多解決方法，如ＩＰ多點(diǎn)傳送和ＣＤＮ（內(nèi)容分發(fā)網(wǎng)絡(luò)）。這兩種方法都需要從特殊的硬件中獲得支持。基礎(chǔ)設(shè)施的裝備和管理的花費(fèi)都非常高，而且也不能從根本上解決問題。近年來，Ｐ２Ｐ網(wǎng)絡(luò)技術(shù)在學(xué)術(shù)上和工業(yè)上都獲得了極大的關(guān)注。在一個(gè)Ｐ２Ｐ系統(tǒng)中，雙方直接進(jìn)行數(shù)據(jù)和其他資源的