P2P流媒体传输外文翻译文献.docx

P2P流媒体传输外文翻译文献.docx

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P2P流媒体传输外文翻译文献

P2P 流媒体传输外文翻译文献

（文档含中英文对照即英文原文和中文翻译）

原文：



Peer-to-PeerStreamingMediaDelivery

Peer-to-PeerArchitecture

Whateverdefinitionshavebeenputuponit,peer-to-peerisaneffectiverallyingcryforanewwayofdoingthings.Manydonotconsideritanewway;ithasbeenarguedthatthecurrentinterestinpeer-to-peerismerelythependulumswingbetweencentralizedanddecentralizedsystems.

Thatcyclecanbedescribedas:

1.Decentralizetoremovebottlenecks

2.Centralizetoincreaseefficiency

Nonetheless,theparticularinflectionpointofresourcesavailableontheInternetatthistimehasallowedpeer-to-peersystemstoexhibitremarkable scalability and resource exchange. This paper brieflydescribesadifferentwayoflookingattheresourcesavailableinthesesystems;itthenillustratestheapplicabilityofpeer-to-peersystemstocontentdelivery.

Peer-to-peerisusedbroadlytodescribeavarietyofnetworksystemsthatgenerallyrunatthepresentation,session,andapplicationlayers,althoughad-hocnetworksandothersystemsusethesameconceptsfromthephysicallayerup.Specifically,peer-to-peerspanscontentdelivery,collaboration, caching, business process automation, supply chainmanagement, grid computing, distributed computation,business-to-business exchanges, data deployment, user to usercommunication,usercommunities,ad-hocnetworks,andtheInternetitself.Perhapspeer-to-peershouldbeconsideredmoreofanarchitecturalapproachthanaspecifictechnologyorbusinessapproach.

Anwayofseeingifaproblemissusceptibletoapeer-to-peerapproachistoask,“Ifeveryclientinthissystemcouldalsoprovidetheservicetheyconsume,wouldtherebeabenefit?

”

Itisnotalwaysthecasethatthereisabenefit;manydatabaseapplications require centralization for security and simplicity of

administration,forexample.

UnusualPeer-to-PeerExamples

Theoft-citedICQandNapsteraretwopioneeringpeer-to-peerexamples.BothprovideanalternativesystemtoDNSfornaming,（anattributeofsomepeer-to-peerdefinitions）andbothprovidetheabilityforuserstodirectlycommunicate,providingthe“person-to-person”aspectalsoassociatedwithpeer-to-peer.

Thereare,however,avarietyofothersystemsprovidingearlierexamplesoftheshifttowardspeer-to-peersystems.Ifpeer-to-peerisconsideredasaqualitywithagradientscale,rangingfromclient-servertoamoreequilateralpowerofcomputingsystems,anysystemthatprovidesahigherratioofserverstoclientscouldberegardedaspeer-to-peer.

Quakewas（andremains）a3donlinemultiplayervideogame.Quake（andlaterQuakeWorld）providedaclient-serversystemforsynchronizedvideogaming.Theserverswereusuallyhighbandwidth,highpoweredsystems,butduetothedemandsofonlinevideogaming,soweretheclients.AndinQuake,theserverwasactuallyembeddedintheclientapplication,blurringthedistinctionbetweenclientsandserversandallowinganynodetoact（byuserselection）asaclientoraserver.AmongmillionsofonlineQuakeplayers,thereeventuallyexistedtensofthousandsofserversontheInternet,andsotheratioofclientstoserversbegantoevenout.

ShoutCastwasdesignedasaplug-intoapopularMP3playerthatenabledlivestreamingofMP3audiooveranHTTPconnection.UserscoulduseShoutCasttocreatearadiostation（ontheInternet）basedontheirMP3collection.Thisallowedservingfromaclientapplication,andincreasedtheeaseforanenduserinconfiguringthisserver.

Peer-to-peerResources

nStorage

nCPU

nBandwidth

StorageandCPUcyclestendtobethetworesourcesmostcommonlycitedinpeer-to-peersystems.Thereare,however,severalresourcesthat,isolated,canbeusedtobetterdescribetherangeofoptimizationsavailablethroughpeer-to-peerapproaches.

Bandwidthisaresourcethatistransientandnon-recapturable.Inthesamewaythatunusedairlineseatscannotberecapturedasaresource,bandwidth,whenavailableandunused,islosttotime.ThefirststageofconsumerInternetexpansioninvolvedagreatdisparitybetweenclientbandwidthandserverbandwidth, butas broadbandequalizesthisresource,itbecomesavailabletoapeer-to-peersystem.

nPresence

nLatency/Proximity

Presencecanbeviewedasaresource.Whenthe„p‟inp2pstandsfor

“person”（asininstantmessagingscenarios）,presenceistheresourceofthatpersonbeingonlineandavailableforcommunicationatthattime.Thisenables onlinecollaboration becauseitprovidesataglancenotificationofavailability.

LatencyandproximityaretworelativelyunremarkedresourcesthatarekeytointeractivesimulationsontheInternet.Quakeprovidesanexampleofalargenumberofservers（Quakeservers）locatedwithanalternativenamespacesystem