Tecnologia punto a punto

Technicalintroduction

Apurepeer-to-peernetworkhasnoconceptofclientorserver,onlyequalnodesatthesamelevel,andatthesametimeactsasaclientandserverforothernodesonthenetwork.Thisnetworkdesignmodelisdifferentfromtheclient-servermodel,inwhichcommunicationusuallygoestoandfromacentralserver.

Aliqua functiones (suchassearch) ofsomenetworks(suchasNapster,OpenNAP,orIRC@invenio)useaclient-serverstructure,anduseaP2Pstructuretoimplementaliae functiones.NetworkslikeGnutellaorFreenetuseapureP2Pstructuretoaccomplishalltasks.

Historia

TheP2ParchitectureembodiesakeyconceptofInternettechnology,whichwasdescribedinthefirstRFCdocument"RFC1,HostSoftware"onApril7,1969.Inthecontextofimplementingmultimediafileexchangewithoutacentralindexserverstructure,thisconcepthasbecomeverycommon.

PureP2P

Thenodeactsasbothaclientandaserver.

Thereisnocentralserver.

Thereisnocentralrouter.

MiscellaneousP2P

Thereisacentralserverthatstoresnodeinformationandrespondstorequestsforsuchinformation.

Nodesareresponsibleforpublishingthisinformation(becausethecentralserverdoesnotsavefiles),letthecentralserverknowwhatfilestheywanttoshare,andletthenodesthatneeditdownloadtheirsharableresources.

Theroutingterminalusestheaddresstoobtaintheabsoluteaddressbybeingreferencedbyasetofindexes.

HybridP2P

ItalsocontainsthecharacteristicsofpureP2PandhybridP2P.

commoda

AnimportantgoalofP2Pnetworksistoenableallclientstoprovideresources,includingbandwidth,storagespaceandcomputingpower.Therefore,whenanodejoinsandrequestsforthesystemincrease,thecapacityoftheentiresystemalsoincreases.ThisisnotpossiblewithaC/Sstructurewithasetoffixedservers.Theincreaseofclientsinthisstructuremeansslowerdatatransmissionforallusers.

ThedistributednatureoftheP2Pnetworkalsoincreasestherobustnessoffailurepreventionbyreplicatingdataonmultiplenodes,andinapureP2Pnetwork,nodesdonotneedtorelyonacentralindexservertofinddata.Inthelattercase,thesystemwillnotcrashatasinglepoint.

WhenP2PisusedtodescribetheNapsternetwork,thepeer-to-peerprotocolisconsideredimportant.However,inpractice,theachievementoftheNapsternetworkisthatthepeernodes(liketheendofthenetwork)uniteacentralindextofulfill.Thisallowsittolocateavailablecontentquicklyandefficiently.Thepeer-to-peerprotocolisjustageneralmethodtoachievethis.

Applications

Point-ad-pointtechnologyhasmanyapplications.Itisverycommontosharefiles continentingvariousformatsofaudio,video,data,etc.Real-timedata(utIPphonecommunicatio,Anychataudioandvideo)canalsobetransmittedusingP2Ptechnologia.

Somenetworksandcommunicationchannels,suchasNapster,OpenNAP,andIRC@find,usetheC/Sstructuretohandlesometasks(suchassearchfunctions)ontheonehand,andusetheP2PstructuretoHandleothertasks.Somenetworks,suchasGnutellaandFreenet,usetheP2Pstructuretohandlealltasks,andaresometimesconsideredtobetrueP2Pnetworks.AlthoughGnutellaalsousesadirectoryservertofacilitatenodestogetthenetworkaddressesofothernodes.

Academicus

DevelopersfromPennsylvaniaStateUniversity,unitedwithMITOpenKnowledgeInitiative,researchersfromSimonFraserUniversity,andsecond-generationInternetP2PworkThegroupisdevelopinganacademicapplicationofP2Pnetwork.ThisprojectiscalledLionShare,basedonthesecondgenerationofnetworktechnology,morespecificallytheGnutellamodel.Themainpurposeofthisnetworkistoallowusersfrommanydifferentacademicinstitutionstoshareacademicmaterials.TheLionSharenetworkusesahybridP2Pnetworktype,whichisamixtureofGnutella'sdecentralizedP2PnetworkandthetraditionalC/Snetwork.Usersofthisprogramcanuploadfilestoaserver,regardlessofwhethertheuserisonline,theycancontinuetoshare.Thisnetworkalsoallowsuseinsharedcommunitiesthataremuchsmallerthannormal.

ThemaindifferencebetweenthisnetworkandotherP2PnetworkscurrentlyinuseisthattheLionSharenetworkdoesnotallowanonymoususers.Thepurposeofthisistopreventcopyrightedmaterialsfrombeingsharedonthenetwork,whichalsoavoidslegaldisputes.Anotherdifferenceistheselectivesharingofindividualfilesfordifferentgroups.Theusercanindividuallyselectwhichuserscanreceivethisfileorgroupoffiles.

Theacademiccommunityneedsthistechnologybecausemoreandmoremultimediafilesareusedintheclassroom.Moreandmoreprofessorsusemultimediafiles,suchasaudiofiles,videofilesandslideshows.Passingthesefilestostudentsisadifficulttask,anditismucheasierifyouuseanetworklikeLionShare.

Leges

InUSlaw,the"BetamaxJudgment"precedentinsiststhatcopying"technology"isnotinherentlyillegal,iftheyhavesubstantivenon-infringingpurposes.ThisdecisionbeforethewidespreaduseoftheInternetisappliedtomostdatanetworks,includingP2Pnetworks,becausethedisseminationofapproveddocumentsisalsopossible.Thesenon-infringingusesincludethedistributionofopensourcesoftware,publicdomaindocumentsandworksnotcoveredbycopyright.Otherjudicialdepartmentscanviewthissituationinasimilarway.

Infact,mostofthefilessharedonP2Pnetworksarecopyrightedpopularmusicandmovies,includingvariousformats(MP3,MPEG,RM,etc.).Inmostjurisdictions,sharingthesecopiesisillegal.Thishascausedmanyobservers,includingmostmediacompaniesandsomeP2Padvocates,tocriticizethisnetworkasahugethreattotheexistingdistributionmodel.Studiesthatattempttomeasureactualmonetarylossesaresomewhatunclear.Althoughtheexistenceofthesenetworksonpapercausedalotoflosses,infact,sincetheestablishmentofthesenetworks,theactualincomehasnotchangedmuch.Regardlessofwhetherthisthreatexists,theRecordingAssociationofAmericaandtheMotionPictureAssociationofAmericaarespendingalotofmoneytryingtolobbylawmakerstoestablishnewlaws.Somecopyrightownersalsopaycompaniestohelplegallychallengeuserswhoengageinillegalsharingoftheirmaterials.

DespitetheBetamaxverdict,P2Pnetworkshavebecometargetsofattacksbyartistsandrepresentativesofcopyrightlicensingorganizations.ThisincludesindustryorganizationssuchastheRecordingAssociationofAmericaandtheMotionPictureAssociationofAmerica.TheNapsterservicewasforcedtoshutdownduetoacomplaintfromtheRecordingAssociationofAmerica.Inthiscase,Napsterdeliberatelyboughtandsoldtheseaudiovisualfilesthatwerenotlicensedfromthecopyrightowner.

Withtheexpansionofmediacompanies’effortstocombatcopyrightinfringement,thesenetworkshaverapidlyandcontinuouslyadjusted,makingitdifficulttoremovethembothtechnicallyandlegally.Thisleadstouserswhoreallyviolatethelawbeingtargeted,becausealthoughtheunderlyingtechnologyislegal,itsabusebyindividualswhospreaditinawayofinfringingcopyrightisobviouslyillegal.

Point-to-point technology

AnonymousP2Pnetworkallowsthepublicationofmaterials,nomatterlegalorlegal,thereislittleornolegalresponsibilityinvariousjurisdictions.Manypeoplesaythatthiswillleadtomoreillegalmaterialsmoreeasilyspread,andeven(somepeoplepointedout)promoteterrorism,requiringregulationintheseareas.Othersobjectedthatthepotentialforillegalusecannotpreventtheuseofthistechnologyforlegitimatepurposes,andthepresumptionofinnocencemustbeapplied,asothernon-P2Panonymousservices,suchasemail,havesimilarcapabilities.

Securitas

ManyP2Pnetworkshavebeenconstantlyattackedbypeoplewithvariouspurposes.Examplesinclude:

Poisoningattacks(providingfileswithdifferentcontentsanddescriptions)

Denialofserviceattacks(makingthenetworkrunveryslowlyorevencompletelycrashing)

Betrayalattacks(Usersorsoftwareusethenetworkbutdidnotcontributetheirownresources)

Insertvirusesinthedata(forexample,thedownloadedortransmittedfilesmaybeinfectedwithvirusesorTrojanhorses)

P2PTrojanhorseofthesoftwareitself(forexample,thesoftwaremaycontainspyware)

Filtering(networkoperatorsmaytrytoprohibitthetransmissionofdatafromP2Pnetworks)

Identityattacks(forexample,trackingUsersonthenetworkandtorturedorlegallyattackedthem)

Spam(suchassendingunsolicitedinformationonthenetwork--notnecessarilyadenialofserviceattack)

IfP2PiscarefullydesignedNetwork,usingencryptiontechnology,mostoftheattackscanbeavoidedorcontrolled.P2PnetworksecurityisinfactcloselyrelatedtotheByzantineGeneralsissue.However,whenmanynodestrytodestroyit,almostanynetworkwillfail,andmanyprotocolswillfailbecauseoffewerusers.

TechnologyOutlook

Technically,apureP2Papplicationmustimplementonlypeer-to-peerprotocols,withouttheconceptofserverandclient.ButsuchpureP2Papplicationsandnetworksarerare.MostofthenetworksandapplicationscalledP2Pactuallycontainorrelyonsomenon-peerunits,suchasDNS.Atthesametime,realapplicationsalsousemultipleprotocols,sothatnodescanactasclients,servers,andpeernodesatthesametimeortime-sharing.Completelydecentralizedpeer-to-peernetworkshavebeeninuseformanyyears,suchasUsenet(1979)andFidoNet(1984).

ManyP2Psystemsusestrongerpeers(calledsuperpeers)asservers,andthoseclientnodesareconnectedtoasuperpeerinastar-likemanner.

Inthelate1990s,inordertopromotethedevelopmentofpeer-to-peernetworkapplications,Sunaddedsomeclassestothejavatechnology,allowingdeveloperstodevelopdecentralizedreal-timechatappletsandapplications.Beforecommunicationbecamepopular.ThisworkwillcontinuetoberealizedbytheJXTAproject.

P2Psystemsandapplicationshaveattractedalotofattentionfromcomputerscienceresearch.SomeoutstandingresearchprojectsincludeChordProject,ARPANET,thePASTstorageutility,P-Grid(aspontaneouslyorganizedemergingcoveragenetwork),AndCoopNetcontentdistributionsystem.

Nunc et situ

ThecurrentsituationofforeignP2Presearch

ForeignacademicgroupscarryingoutP2PresearchmainlyincludetheP2PWorkingGroup(P2PWG),GlobalGridForum(GlobalGridForum,GGF).ThemainpurposeoftheP2PworkinggroupistoacceleratetheestablishmentofP2Pcomputinginfrastructureandcorrespondingstandardizationwork.AftertheestablishmentofP2PWG,theterminologyinP2Pcomputingwasunified,andrelateddraftswerealsoformed,butprogressinstandardizationworkwasslow.P2PWGhasbeenmergedwithGGF,andtheforummanagesP2Pcomputingrelatedwork.GGFisresponsibleforrelatedstandardizationworksuchasgridcomputingandP2Pcomputing.

Fromtheperspectiveofforeigncompanies'supportforP2Pcomputing,Microsoft,SunandIntelhaveinvestedheavily.MicrosoftestablishedthePastryprojectgroup,whichismainlyresponsiblefortheresearchanddevelopmentofP2Pcomputingtechnology.MicrosoftCorporationhasreleasedPastry-basedsoftwarepackageSimPastry/VisPastry.RiceUniversityalsoreleasedtheFreePastrysoftwarepackagebasedonPastry.

InAugust2000,IntelannouncedtheestablishmentofaP2PworkinggrouptoformallycarryoutP2Presearch.Aftertheestablishmentoftheworkinggroup,itactivelycooperatedwithapplicationdeveloperstodevelopP2Papplicationplatforms.In2002,IntelreleasedtheAcceleratorKit(P2PAccelerationToolkit)andP2PsecurityAPIsoftwarepackagebasedonthe.Netinfrastructure,allowingMicrosoft.NETdeveloperstoquicklybuildP2PsecureWebapplications.

SuncompanylaunchedtheJXTAprojectwithJavatechnologyasthebackground.JXTAisanopensourceP2PplatformbasedonJava.Anyindividualandorganizationcanjointheproject.Therefore,theprojecthasnotonlyattractedalargenumberofP2Presearchersanddevelopers,butalsohasreleasedaninstantchatsoftwarepackagebasedonJXTA.JXTAdefinesasetofcoreservices:authentication,resourcediscoveryandmanagement.Intermsofsecurity,JXTAhasaddedanencryptionsoftwarepackage,allowingtheuseoftheencryptionpackagefordataencryption,soastoensuretheprivacy,authenticityandintegrityofthemessage.OntopoftheJXTAcore,variousotheroptionalJXTAservicesincludingcontentmanagement,informationsearch,andservicemanagementarealsodefined.Onthebasisofcoreservicesandoptionalservices,userscandevelopP2PapplicationsonvariousJXTAplatforms.

ThecurrentstatusofP2PresearchinChina

·PekingUniversity-Maze

MazeisthePekingUniversitynetworkApeer-to-peercomputingfilesharingsystemthatintegratescentralcontrolandpeer-to-peerconnectionsdevelopedbythelaboratoryissimilarinstructuretoNapster,andthepeer-to-peercomputingsearchmethodissimilartoGnutella.Acomputeronthenetwork,whetherontheinternalorexternalnetwork,canfreelyjoinandexittheMazesystembyinstallingandrunningtheMazeclientsoftware.Eachnodecansharefilesinoneormoreofitsowndirectorieswithothermembersofthesystem,andcanalsoshareresourcesofothermembers.Mazesupportskeyword-basedresourceretrieval,anditcanalsobeobtaineddirectlythroughfriendrelationships.

·TsinghuaUniversity-Granary

Granaryisapeer-to-peercomputingstorageservicesystemindependentlydevelopedbyTsinghuaUniversity.Itstoresdatainobjectformat.Inaddition,GranarydesignedaspecialnodeinformationcollectionalgorithmPeerWindow,astructuredoverlaynetworkroutingprotocolTourist.

·HuazhongUniversityofScienceandTechnology—AnySee

AnySeeisalivevideosystemdesignedanddevelopedbyHuazhongUniversityofScienceandTechnology.Itadoptsaone-to-manyservicemode,supportspartialNATandfirewalltraversal,andimprovesthescalabilityofthevideolivebroadcastsystem;atthesametime,itusesthenear-castprincipleandtheideaofdomain-basedscheduling,andusestheLandmarkroadsignalgorithmtodirectlybuildatree.Theconstructionofthemulticasttreeontheapplicationlayerovercomestheloadimpactoftheconstructionandmaintenanceoftheconnectiongraphinone-to-manymodesystemssuchasESM.

Formoredetailedintroduction, videbis [ChineseComputerSocietyNewsletterPage38-51ZhengWeiminetal.IntroductiontoPeer-ad-PeerComputingResearch]

R&DProducts

GuangzhouDigitalSoftwareTechnologyCo.,Ltd.-Poco

POCOisChina’slargestP2Pusersharingplatform,thethirdgenerationwithsecurity,flowcontrol,andnocentralserverTheP2PresourceexchangeplatformisalsooneofthefewprofitableP2Pplatformsintheworld.Amassive26millionusershavebeenformed,withanaverageof585,000onlineandapeakonlinepeakof710,000,allofwhicharebroadbandusers.BecomethenumberoneP2PsharingplatforminChina.[a]

ShenzhenDianshiSoftwareCo.,Ltd.-OP

OP-alsoknownasOpenextMediaDesktop,anetworkentertainmentcontentplatform,NapsterThesuccessor,itcanfindthemusic,movies,software,games,pictures,booksandvariousdocumentsyouwantinthemostdirectway,andsharethefilecapacityofhundredsofmillionsoffilesonlineatanytime.picture".OPintegratesInternetExplorer,WindowsMediaPlayer,RealOnePlayerandACDSee,andisadomesticonlineentertainmentcontentplatform.[a]

P2P-basedonlineLiveTV-PPLive

PPLiveisaSharingsoftwareforlarge-scalelivevideostreamingontheInternet.Itusesameshmodeltoeffectivelysolvethebandwidthandloadlimitationofcurrentnetworkvideo-on-demandservices.Themoreusers,thesmoothertheplayback,andtheoverallservicequalityisgreatlyimproved!(Duringthe2005SuperGirlFinals,thissoftwarewasverypopular,andthereweretensofthousandsofviewerswatchingHunanSatelliteTVthroughit)

High-definitionvideo-in-demandbasedonP2Ptechnology-BaofengYingyin

BaofengyingyinisthefirstdomesticrealHDvideoon-demandsoftware,whichusesmatureP2Ptechnologyanduniquevideocompressiontechnologytorealize1Mbandwidthtowatch720PHDvideosmoothly.BaofengYingyinCompanyiscommittedtoimprovingtheviewingexperienceofChineseonlinevideousers.Itfocusesonhigh-speedtransmissiontechnologyandhigh-proportionvideocompressiondecodingtechnologyofhigh-definitionvideointheexistingnetworkenvironment,andhasbecometheleaderofChina'sInternethigh-definitiononlineon-demandservices.