Conceptintroduction
Thatistoplaythecorrespondingvideoprogramsaccordingtotheneedsofusers,whichfundamentallychangesthedeficienciesofusersinpassiveTVwatchinginthepast.WhenyouturnontheTV,youdon’tneedtowatchcommercials,anddon’tbeinahurryforacertainprogram.Youcandirectlyorderthecontentyouwanttowatchatanytime.NeedtobuyvideotapesorVCDdisks,anddonotneedvideorecordersorVCDplayers.Thisisthedreamthatinformationtechnologybringstoyou.Itdeliversvideoprogramstothousandsofhouseholdsaccordingtopersonalwishesthroughmultimedianetworks.
Lookingattheapplicationofbroadbandnetworks,VODistheclosesttopeople’slives,butitisalsothemosttechnicallydifficult.Inthewordsofthecommonpeople,therearehighways,sotheremustbecarsrunning.VODapplicationsarethemosteye-catchingcarsonbroadbandmultimedianetworks.
VODtechnologycanbeappliednotonlyinthebroadbandnetworkoftelecommunications,butalsointhebroadbandnetworkofresidentialareaLANandcabletelevision.Nowadays,intheprocessofbuildingsmartcommunities,computernetworkcablinghasbecomeanindispensablepart.CommunityuserscanrealizeVODvideo-on-demandapplicationsthroughcomputers,TVsets(withset-topboxes),etc.,whichenrichespeople’sculturallife;Thetwo-waytransformationallowsthemajorityofTVuserstoordervideoprogramsthroughthecableTVnetwork.
Implementationprocess
Thevideo-on-demandsystemismainlycomposedoffilmsourcelibrarysystem,streamingmediaservicesystem,shadowcabinetsystem,transmissionandexchangenetwork,userterminalequipmentset-topbox+TVorpersonalcomputercomposition.
Therealizationprocessofvideo-on-demand:Whenausersendsarequestforavideo-on-demand,thestreamingmediaservicesystemwillretrievetheprograminformationstoredinthesourcelibraryaccordingtotheon-demandinformation,andusevideoandaudiostreamingfiles,Itistransmittedtotheuserterminalthroughahigh-speedtransmissionnetwork.
On-demandservicesaregenerallyimplementedbyunicastnetworks.Theso-calledunicastistheuseofaprotocoltotransmitIPdatapacketsfromaninformationsourcetoadestination.Atthistime,informationisreceivedandtransmittedonlyintwoBetweennodes.InIPunicast,thereisonlyonesenderandonereceiver,andbothpartieshaverelativelyfixedIPaddresses.IPunicasttransmissionisthemainmethodofEthernettransmission.Mostofthedataonthenetworkistransmittedintheformofunicast,andHTTP,RTSP,SMTP,FTPandTelnetareallusedasTCPtransmissionprotocolsinthenetworkinsinglemode.Waytowork.Thecharacteristicofunicastisthateachterminaloccupiesacertainbandwidth.Whenthebandwidthisfull,otherterminalscannotconnecttotheserver.
Structure
Serversystem
Theserversystemismainlycomposedofvideoserver,filemanagementserver,audioandvideoserver,internalcommunicationsubsystemandnetworkinterface.Thefilemanagementserverismainlyresponsibleforuserinformationmanagement,billing,filmandtelevisionmaterialssorting,securityandconfidentialityandothertasks.Theinternalcommunicationsubsystemmainlycompletesthetransmissionofinformationbetweenservers,theexchangeofbackgroundvideomaterialsanddata.Thenetworkinterfacemainlyrealizesdataexchangewiththeexternalnetworkandprovidesaninterfaceforuseraccess.Thevideoserverismainlycomposedofastoragedevice,ahigh-speedcache,andacontrolmanagementunit.Itsgoalistorealizethecompressionandstorageofmediadata,aswellastheretrievalandtransmissionofmediainformationonrequest.Therearemanysignificantdifferencesbetweenthevideoserverandthetraditionaldataserver,anditisnecessarytoincreasealotofdedicatedsoftwareandhardwarefunctionequipmenttosupportthespecialneedsofthebusiness.Forexample:mediadataretrieval,real-timetransmissionofinformationflow,encryptionanddecryptionofinformation,etc.ForaninteractiveVODsystem,theserversystemalsoneedstorealizethesimulationofreal-timeuserrequestprocessing,accesspermissioncontrol,andVCR(VideoCassetteRecorder)functions(suchasfastforward,pause,rewind,etc.).
Networksystem
Thenetworksystemincludestwoparts:thebackbonenetworkandthelocalnetwork.Becauseitisresponsibleforthereal-timetransmissionofvideoinformationstreams,itisanextremelycriticalpartthataffectstheperformanceofthecontinuousmedianetworkservicesystem.Atthesametime,thenetworkpartofthemediaservicesystemhasahugeinvestment,soitisnecessarytoconsidernotonlythehighbandwidthrequirementsofcurrentmediaapplications,butalsotheneedsoffuturedevelopmentandbackwardcompatibilitywhendesigning.Currently,thenetworkphysicalmediathatcanbeusedtoestablishthisservicesystemaremainly:CATV(cabletelevision)coaxialcable,opticalfiberandtwistedpair.Themainnetworktechnologiesusedare:FastEthernet,FDDIandATMtechnologies.
Clientsystem
Thiswayofon-demandTVis:multiplevideostreamsstarttosendthesamecontentatacertainintervalinsequence.Forexample,twelvevideostreamsstartonetosendthesametwo-hourTVprogrameverytenminutes.
Atthattime,on-demanduserscanwatchandenjoytheirfavoriteprogramsaslongastheyoperatetheremotecontrolwithasingletap,andcanadjusttheprogress,speed,etc.oftheshowatanytime.TheemergenceofVODmakestheTVamediumthatcanobtaininformationrandomly,morelikeabookoranewspaper,whichcanbebrowsedandadjusted,andisnolongerlimitedtoacertaintime,dateandfixedprogramrestrictions..
Birthbackground
Intheprocessofnetworkvideotransmission,usersareusuallyrequiredtodownloadaudioandvideofilestothelocalcomputerbeforeplayingthem.AlthoughthismethodmakesitpossibletotransmitmultimediainformationontheInternet,italsobringsthreeprominentproblems:
(1)Sincemultimediainformationmustbedownloaded,thedatavolumeofmultimediainformationisusuallyVerylarge,inthecaseofalowaccessrateforordinaryusers,averyshortvideoclipmaytakealongtimetodownload.
(2)Sincetheprogrammustbedownloadedtothelocalcomputerbeforeitcanbeplayed,thiswillinevitablyoccupythestorageresourcesofthelocalcomputer.
(3)Copyrightissues.Becauseaftertheuserdownloadstheaudioandvideofilestotheharddisk,theymayhavetore-distributethesematerials,sotheintellectualpropertyrightsoftheproductionunitmaybedamaged.
Inthiscontext,"streaming"cameintobeing.Itdrawsonthecomputer'sownwayofusingthebufferareatoimprovethefilerunningspeed,andconsidersplacingabufferontheplaybacksidetosolvetheproblemofservicequality.Streamingtransmissiondividesmultimedia,suchasanimation,audioandvideo,intocompressedpackagesthroughaspecialcompressionmethod,andtransmitsthemcontinuouslyandinrealtimefromthevideoservertotheuser'scomputer.Inasystemthatusesstreamingtransmission,usersdon’thavetowaituntiltheentirefileisdownloadedtoseethespecificcontentlikenon-streamingplayback.Theyonlyneedtodelaythestartofafewsecondsortensofsecondstousethecorrespondingplayback.Thedevicedecompressesthecompressedanimation,audio,videoandotherstreamingmultimediafilesforplayback,andtheremainingpartofthemultimediafileswillalsocontinuetobedownloadedinthebackgroundserver.Thiskindofmultimediatransmittedbytheideaof"streaming"iscalledstreamingmedia.
1.ManymultimediaformatsareusedontheInternet:
(1)RealNetwoks'sRealsystem;
(2)Microsoft'sWindowsMediaTechnology;
(3)Apple’sQuickTime,theyarethethreemainstreamonlinestreamingmediatransmissionsystems.
2.Streamingmediacontentproduction:
(1)Conversion/transcodingsoftware:canconvertaudio,videooranimationmediafilesincommonformatsintoastreamingserverthroughcompressionStreamingstreamingformatfile,itisthemostbasicproductionsoftware,actuallyanencoder(Encoder),commonsoftware:RealProducerandWindowsMediaEncoder
(2)StreamingmediaeditingSoftware:Editstreamingmediafiles,oftenbundledwithtranscoding/transcodingsoftware.
(3)Synthesissoftware:Usingsynthesissoftware,youcansynchronizevariouspictures,sounds,texts,videos,slidesorwebpages,andsynthesizeastreamingmediafile.Commonsoftware:RealShow,RealPresenterandWindowsMediaAuthor.
(4)Programmingsoftware:TheSDKprovidedbythestreamingmediasystemallowsdeveloperstoperformsecondarydevelopmentonthesystem.UsingtheSDK,developerscanusuallydevelopnewstreamingdatatypes,createclientapplications,andcustomizestreamingmediasystems.
Classificationintroduction
Accordingtodifferentfunctionalrequirementsandapplicationscenarios,therearemainlythreetypesofVODsystems:NVOD,TVOD,andIVOD.
NVOD(Near-Video-On-Demand),itcanbecallednear-on-demandTV.Thiswayofon-demandTVis:multiplevideostreamsstarttosendthesamecontentatacertaintimeintervalinsequence.Forexample,twelvevideostreamsstartonetosendthesametwo-hourTVprogrameverytenminutes.IfuserswanttowatchthisTVshow,theymayhavetowait,butthelongestwillnotexceedtenminutes,theywillchoosetowatchitatacertaintimestartingpointclosesttothem.Inthisway,onevideostreammaybesharedbymanyusers.
TVOD(TrueVideo-On-Demand),itiscalledtrueon-demandTV,itreallysupportsclickandplay.Whentheusermakesarequest,thevideoserverwillimmediatelydeliverthevideocontenttheuserwants.Ifanotheruserputsforwardthesamedemand,thevideoserverwillimmediatelystartanothervideostreamtransmittingthesamecontentforhim.However,oncethevideostreamstartstoplay,itmustbeplayedcontinuouslyuntiltheend.Inthisway,eachvideostreamisconvertedtoacertainuserservice.
IVOD(InteractiveVideo-On-Demand),calledInteractiveVideo-On-Demand.Itisanimprovementovertheprevioustwomethodstoalargeextent.Itcannotonlysupportclickandplay,butalsoallowsuserstointeractivelycontrolthevideostream.Atthistime,theusercanplay,pause,rewind,fastforward,andautomaticallysearchtheprogramjustlikeoperatingatraditionalvideorecorder.
OCVOD(One-wayCableVideo-On-Demand),calledon-demandTVbasedonone-waycablenetwork,referredtoasTVondemand.ItisactuallyanimplementationofIVOD,basedonaone-waycableTVnetwork,andwiththehelpofathird-partybroadbandnetwork,toachievepoint-and-playinteractiveTVondemand.TheadvantageofTV-on-demandisthatsmallcableTVoperatorsdonotneedtoinvestalotofmoneyfortwo-waynetworktransformation,whichgreatlyreducesthesystemconstructioncostofsmallcableTVoperatorsandthethresholdfordevelopingon-demandTVservices.
Onlybyusingthecorrespondingterminalequipment,userscancontactandinteroperatewithacertainserviceorserviceprovider.IntheVODsystem,aTVsetandaset-topbox(Set-topBox)arerequired.Insomespecialsystems,acomputerwithalarge-capacityharddiskmayberequiredtostorethevideofilesfromthevideoserver.Intheclientsystem,inadditiontothecorrespondinghardwaredevices,relatedsoftwareisalsorequired.Forexample,inordertomeettheuser'smultimediainteractionneeds,theinterfaceoftheclientsystemmustbemodified.Inaddition,whenperformingcontinuousmediaplayback,issuessuchasmediastreambuffermanagement,audioandvideodatasynchronization,networkinterruptionandstudiointerruptioncoordination,allneedtobefullyconsidered.
ItcanbeseenthatalthoughtheVODserviceisveryattractive,itsimplementationtechnologyisnotan"easybone".However,withtherapiddevelopmentofnetworktechnology,computertechnology,storagetechnology,etc.,thedayforuserstofullyenjoythefunofVODisnotfaraway.Atthattime,on-demanduserscanwatchandenjoytheirfavoriteprogramsaslongastheyoperatetheremotecontrolwithasingletap,andcanadjusttheprogress,speed,etc.oftheshowatanytime.TheemergenceofVODmakestheTVamediumthatcanobtaininformationrandomly,morelikeabookoranewspaper,whichcanbebrowsedandadjusted,andisnolongerlimitedtoacertaintime,dateandfixedprogramrestrictions..
AlthoughVODfirstappearedtobettermeettheneedsofusersforindependentwatchingofvideoprograms,butwiththecontinuousadvancementofVODtechnology,itswide-rangingapplicationwillaffectmasscultureandbusinessoperationmodels.Haveastrongimpact.VODcannotonlyprovideenduserswithdiversifiedmediainformationstreamstoexpandpeople’sinformationchannelsandenrichpeople’sspirituallife;butalsoinhospitals,hotels,airplanesandotherplacesofentertainment,companystafftraining,long-distancemarketresearch,companyTheadvertisingbusinessandotherfieldswillgraduallybefloodedwithnewapplicationsofVODtechnology.
IP-basedVOD
Duetothelimitationofnetworkbandwidth,especiallythelimitationofWAN(WideAreaNetwork)bandwidth,thetransmissionofhigh-speeddataonWANisnotyetmature,sohereweareTheIP-basedvideo-on-demand(VOD)technologythatItalkedaboutreferstotheuseofEthernetasaVODtransmissionplatformtoachievelocal-scaleTVOD(trueVOD)technology.Sincewecanalsoprovidevariousvalue-addedservicessuchasInternetaccess,traditionaldataservices,IPtelephony,videotelephony,videoconferencing,etc.onthisEthernetplatform,weareinanIP(herereferstoEthernet)asAvarietyofbusinessexchangesarerealizedonthebasicexchangeplatform,sothatpeoplecanrealizehigh-speedinformationinteractioninasmallarea,andthisalsolaysacertainfoundationforrealizinghigh-speedinformationinteractioninthefuture.Inthefuture,withthefurtherdevelopmentofopticalfibertechnologyandroutertechnologyandthefurtherimprovementofvariousIPprotocols,the"informationhighway"willeventuallyberealized.Inthisway,wecanachievehigh-speeddatatransmissionandguaranteethequalityofvariousreal-timeservicesinaWAN.Onlythencanwesaythatwehaveenteredacompletelyinformationsociety.
One.DifficultiesinimplementingIP-basedVODtechnology
1.QualityofService(QoS)ofIP-basedreal-timeswitching
BecauseIPadoptstheformofdatapackagingandpacketswitching,italsoallowsdifferentpacketsizes.Therefore,thereal-timetransmissionofdatacannotguaranteethequality.Thisismainlycausedbytheuncertainnetworkdelaytimecausedbydatapacketcollision.Highvideotransmissioncannotfullyguaranteeitsqualityofservice(QoS).
2.Videoserverprocessingcapabilities
Therearemanytypesofvideoservers.Generallyspeaking,theyareclassifiedbasedonthenumberofuserstheysupportandthesystemtheyarebasedon.Therearemainlythefollowingforms.
(1)Videoserverbasedongeneral-purposecomputer
Thiskindofvideoserverisrelativelysimple.Fromadevelopmentpointofview,theyaregenerallyrudimentaryproducts,withsimpleandlimitedfunctions,andthenumberofsupportedusersisalsolimited(about50households).Becauseofitslowprice,ithasacertainmarketinsmallapplications.
(2)Videoserversbasedonadvancedworkstations
Videoserversbasedonadvancedworkstationsaresomemanufacturersthatproducelarge-scalecomputersusingtheiradvantagesincomputers,usinghigh-performancecomputersasBasically,addsomerelatedhardwarethatsupportsvideodataaccess,andoptimizethesystemtoachievethefunctionofageneralvideoserver.Theycangenerallysupportmedium-scalenetworks(50-1000households),buttheirhighpricesmakeordinaryusersdaunting.
(3)Videoserverbasedondedicatedhardwareplatform
Videoserverbasedondedicatedhardwareplatformisthatsomehardwaremanufacturersusededicatedhardwaretoaccessvideodata.Becauseitusesdedicatedhardwaretoachieveaccesstovideodataandfocusesonsolvingitsmassivestorageproblem,itisunmatchedbythefirsttwovideoserversintermsofspeedandstoragecapacity.Butitalsohasitsshortcomings.Firstofall,becauseitusesspecialhardwareandsolvesalargenumberofstorageproblems,goodqualityalsohasagoodprice,soitdeterminesitsexpensiveprice.Secondly,becausetheyaredevelopedbysomehardwaremanufacturersthemselves,theyareverydependentonthehardware,sotheirversatilityisverypoor,whichlimitstheirdevelopment,andtheyaregenerallyusedinlarge-scalenetworkapplications.
Tosumup,therearestillmanyunsatisfactoryaspectsofthevideoserver(suchasprice,processingpower,versatility,etc.),butwiththedevelopmentoftechnology,itwilleventuallymature,andthisdaywillnotItwillbetoolong.
3.Largeamountofdatastorage
Becausethedatavolumeofamovieisverylarge(1.2~1.5GB),savingthemoviehasbecomeaverybigproblem,thatis,thestorageoflargeamountsofdata.
TheaboveproblemsaretechnicallydifficultproblemsforVODtechnology.Inresponsetotheaboveproblems,wehaveintroducedadistributedhierarchicalstructuresystembasedontheexistingtechnologyasoursolution,whichisasolutionbasedonIP(herereferstoEthernet)technology.
Currentsituationandfuture
Withtheincreasingdigitizationandinteractionofmediaservices,theadvancementofcompressiontechnologyhasledtothecontinuousreductionofbandwidthrequirements,andtoday'smarketisundergoingamajorchange.Withtheincreasingnumberofconsumerservices,networkaccessbandwidthhasbeenwidelypopularized.Theintegrationoftheabovetrends,superiortelecommunicationsperformanceandrichmediacontentisbringingearth-shakingchangestothetransmissionofvideo-on-demandservices.Theincreasingmaturityoftechnologymakesiteasyforuserstoaccesscontent,soeveryoneisbeginningtoexpecttobeabletoexperienceultra-high-qualityvideosandotherrichmediatypesanytime,anywherethroughwiredandmobiledevices.Inaddition,contentownersarealsoseekingnewandmoreeffectivewaystospreadtheircontentmorewidelyandprofitfromitinasmanywaysaspossible.The"perfectstorm"broughtaboutbycontentavailability,technicalcapabilities,andubiquitoushigh-speedtelecommunicationsinfrastructurehasopenedthedoortoarapidtransitiontolarge-scale,high-yieldvideo-on-demand.
However,therapidgrowthofVODwillinevitablybringmanychallengesandopportunitiestofixednetworkoperators,suchas:congestionmanagement,contentlocationservices,billing,recommendationengines,storage,andtimelydelivery.Tomakethisdreamcometrue,allauxiliaryinfrastructuresmustbeputinplaceandthefollowingelementsmustbeimplemented:high-speedaccessandtransmission,viableserversolutions,sufficientandwidelydistributeduserandnetworkstorage,mediaprocessing,Deliveryofroutingdiversity,contentprocessing,andQoS(trafficandcongestionmanagement).Atthesametime,theoptimizedarchitectureforon-demandcontentandmediacontentdeliverymustalsobeimplementedandfullyfunctional.
Oneofthekeyfactors:media
Thechangesthataretakingplaceinthemedia,technologyandtelecommunicationsfieldscanensurethatVODwillbecomeanimportantdrivingforceinthefieldofmediatransmissioninthenextfewyears.Amongthem,media,asthekeytotheentireindustry,willprovideavarietyofavailablecontentforasmanydevicesaspossible.Ofcourse,inamediasalesmarketwherecompetitionhasbecomefierce,themedialayoutmustbecoordinated,carefullyplannedandcarefullyanalyzed.Byin-depthunderstandingofeachuser’spurchasehistory,downloadpreferences,andpreferredtechnologyanddeliverymethods,futuresalespotentialcanbemaximized.Equallyimportantandcriticalisthatvideo-on-demandisbeginningtoplayanincreasinglyimportantroleinthemarket.ThemediaindustryhasincreasinglyrecognizedthatVODisareliableandlong-termallyinthebattleformediadataretrievalcapabilities.Inaddition,itcanalsofacilitatethedeliveryof"tripleplayservices"ofvoice,videoanddata.
Keyfactortwo:Technology
Technologyplaysanequallyimportantroleinthedeliveryofvideoondemand.Thecontentisstoredinastoragedevice(usuallyaDVD)inthehandsoftheuser.TechnologyandmarketacceptancedeterminewhetherVODHDon-demandcanbecomeabetterreality,soaninterestingchangehasbeenstaged.Thecontentstoredontheclientinthepastisbeingmigratedtothenetwork,andthenthecontentisextractedfromoneormoreserversandsenttousersondemand.Thiscansimplifyvariousrequirements,suchaslarge-capacitystoragearrays,complexinteractionsbetweenpeer-to-peerservers,powerfulpacketprocessingcapabilities,datacollectionandbillingalgorithms,andnetworkscapableoftransmittingincreasinglyrichmediacontent.Ofcourse,ifthecontentcannotbedeliveredtousersinatimelyandaccuratemanner,allthisisemptytalk.Measurablequalityofservice(QoS)mustbeguaranteed.Atthesametime,trafficmanagementisessentialinnetworksandprocessor-dependenttransmissionenvironments.Itisnecessarytodesignandimplementadeliverystructurethatcanprovideafullyguaranteedworkspaceintheworstcase.
Thethirdkeyfactor:telecommunications
Thetelecommunicationsindustryisthetoppriorityoftheentiredeliveryblueprint.Thethreeindustriesarefundamentallydependentontheothertwoindustries,andthetelecommunicationsindustryisparticularlyimportant.Leavingthereliablebroadbandinfrastructurethatsupportsthem,nomatterhowrichthecontentis,nomatterhowcomplexthedatacollection,storageandbillingmodelarepowerful,itisalsoaflowerinthemirrorforusers.Aseriesofrecentdevelopmentsinthetelecommunicationsfieldhavereshapedtheroleofthenetworkinmanyways,especiallyforon-demandcontent.
Ofcourse,thebiggestchangeistheirreversibledevelopmentfromrigid,TDM-basednetworkstomoreflexibleIPnetworks.Althoughthetransformationofthetelecommunicationsindustryisstillintheearlystages,thesituationwillchangequickly,andtheentireserviceprovidernetworkhasbeguntotransformtoIPandMPLS.ItisworthmentioningthatIMS,becauseitwillbecomethefocusofon-demandvideointhenearfuture.3GPPinitiallyregardedIMSasawaytoprovidecontenttomobiledevices,anditismoreregardedasthebackbonetechnologyplatformfortransmittingmultimediacontentinvariousnetworks.IMShasapromisingfuture:Aslongasitiswidelydeployed,serviceproviderscanprovideanycontenttoanydeviceofanyuseranywhereintheworldthroughanynetworkandusinganyaccessmethod,andcancalculateaccordingtotheuser'spreferredmethodstoredinthenetworkdatabase.fee.ThisincrediblefunctioncapturestheessenceofstreamingvideoandVODasanecessaryconditionforbusiness.Themedia,technology,andtelecommunicationsinfrastructurethatcananalyzeandutilizecustomerpreferences,consistentlyguaranteehighQoS,andprovidecontentbasedontheneedsofusersratherthanserviceproviderscanbedescribedasperfect.However,theroadaheadforservicedeliveryisstilltortuous.
Currentarchitecture
WiththeincreasingpopularityofVODandthecontinuousintegrationofserviceproviders,technologydesigners,andmediaowners,thedeliveryarchitectureisalsoevolving.ThemostfamousVODarchitectureusedinlargenetworksisusuallycalledtheSHE-VHO-VSOmodel.
SHE-VHO-VSOmodel-Thisarchitectureisahierarchicalarchitecture:"SuperHeadend"(SHE)gatherscontentfromalargeareaoracrossthecountryandProvidereal-timenationwidecontentwithinthescope,usuallyusingIPasthenetworklayerprotocol.The"VideoCentralOffice"(VHO)andSHEintegratelocalandregionalcontentintoacontentportfoliotoensurethesupplyofnationalandlocalcontent.Finally,the"VideoSwitchingOffice"(VSO)mapsdifferentcontentfromthenetworktotheaccessdomainfordeliverytousers.
Thismodelisverysuitablefortraditionalcontentdelivery;however,aseveryone’sinterestinon-demandservicescontinuestoincreaseanditsproportionintherevenuestreamincreases,avarietyofbusinessproblemsbegintoappear.SincetheoverallgoalsofallVODdistributionmodelsaretominimizedeliverydelays,maximizenetworkservicereliability,createabusinessenvironmentthatiseasytomanage(andthereforeeasytobill),andensureareliableandpredictablemediastreamingenvironment,thereisDifferentarchitecturalschemes.Sincetrafficbottlenecksarethemostcommonanddifficultprobleminserver-basednetworks,abandoningasingleserversolutionisanaturalchoice.
Distributedservermodel-ideallythismodelcanworkwell.However,sincemostnetworksareverycomplex,therearesomepotentialproblemswithcontentfromasinglesite.Forthisreason,amulti-serverarchitectureisusuallydeployedtosendcontentfrommultipleserverstoasingleclient.Inthisway,theriskoffailurecanbedistributedtomultipledevices,andatthesametimeeliminatethebottleneckoftheserverinandout.Thecontentdownloadinthismodelisdrivenbythereceiverinsteadofthetransmitter,sothatthereisnoneedtocoordinatethevariousserversparticipatinginthedownload.Inaddition,requestsforservercontentareperformedattheblocklevel,whicheliminatestheneedforcomplexandtime-consumingpacketprocessing.Finally,thebandwidthoccupancycanbeadaptivelymanagedamongtheparticipatingservergroups,sothatontheonehand,theserverloadcanbekeptrelativelybalanced,andontheotherhand,thepossibilityofseriousbusinessinterruptioncausedbyserverfailurecanbeeliminated.
Peer-to-peertransmission-followingthedistributedservermodelcomesthesubjectchange.Theserverthatisultimatelyresponsiblefordeliveringcontenttousersisoftencalledastreamingengine.Inapeer-to-peerenvironment,themainstreamenginecooperateswithpeer-to-peerserverstodownloadrelevantdatablocksfromthecooperativedeviceandsendthemtousers.Thisallowsdifferentserversandpathstosharetransmissionresponsibilities,therebyimprovingtheoverallefficiencyofthesystem.
Constituentsections
Front-endprocessingsystem
Thefront-endprocessingsystemgenerallyconsistsofvideoserver,diskarray,programdatabase,broadcastcontrolsystemAndothercomposition.Thehigh-speeddatatransmissioncapabilityofthevideoserverensuresthatusershavenearlyinstantaccesstoalargenumberoffilms,videoprograms,games,businessinformationandotherservices.Itsoutstandingadvantageisthatseveraluserscanwatchthesameprogramfromdifferenttimestartingpoints,whichavoidsthesituationthatthewonderfulprogramismonopolizedbyoneuser,orafteracertainuserbroadcaststheorder,otheruserscanonlypassivelyfollowthesituation,whichisarequirementfortheuseron-demandRelativelyconcentratedvenuesareparticularlysuitable.
VODvideoserverstoresalargenumberofcompressedimageprogramsandcanprovideuserswithrequiredprogramcopiesthroughthenetwork,andcanalsoincludereal-timeMFEGencoderstoaccesslivebroadcasts.Theprogramdatabaseisanarchivesystemthatstoresalargenumberofcompressedfilmprograms,whichcanbedownloadedtothevideoserverinbatches.TheVODvideoservercontrolstheplaybackofprogramsthroughdirect,real-time,two-wayinteractionwithusers,includingprogramselection,startandendoftheplaybackprocess,controlofplaybackspeed,anddynamicswitchingbetweendifferentprograms.
Controlmanagementsystem
TheTVset-topboxcontrolmanagementsystemisasignalingtransmissionnetworkusedtomanagetheconnectionofuserstotheVODvideoserver.SincetherecanbemultipleVODvideoserversintheactualVODsystem,thecontrolandmanagementsystemadoptstwo-levelgatewaymanagement.Thefirstlevelrealizestheselectionofdifferentchannelsinthedigitalbroadbandswitchingsystemandtransmissionsystem;thesecondleveliscompletedinTheselectionofaspecificprogramonaVODvideoserver.
ThespecificprocessofVODsignalinganddataflowpathisasfollows:
(1)Connecttheset-topboxandaccessthepopulationdevicethroughthepresetsignaling;thatis,theS3isconnected,andtheVODsystemwilllisttheservicesFromthepopulationtotheuser;
(2)Accordingtotheuser'srequest,thepopulationselectstherelevantvideoserver,thatis,connectstoS4,andprovidestheserviceprimeguide;
(3)TheinitializationofS4canbecompletedbyaset-topboxoravideoserver;theservicepopulationprovidesroutinginformation,andtheserverprovidesaprogramlist;
(4)Theuserselectsaprogramfromtheprogramlistandtransmitsthesignalingtothevideoserver;
(5)Sendtheprogramfromthevideoservertotheset-topboxthroughthenetworkoperation,thatis,connecttoP1,andloadtheprogramfromthevideolibrarytothecurrentfrequencyserverifnecessary;thatis,connecttoP;
(6)OthersignalingchannelsS5,S6,andS7allservethemonitoringandrecordingoftheoperationcenter.
ATMdigitalfixed-bandswitchingsystem
Managementcapability,point-to-pointexchangeableinteractiveVODsystem,itsserver,network,accessequipment,userreservationEquipment,etc.canruninmultipletypesofvideocompressionmodesandenvironmentswithdifferentbandwidthrequirements.Thevideoservercantakeouttheprogramsdemandedbytheuserfromthevideolibraryaccordingtotheuser'srequirements,andtransmitittotheuserthroughtheATMnetwork.VideoinformationisgenerallycompressedandcodedbyMPEGstandards,loadedwithATMcells,andtransmittedontheATMnetwork.Theremaybemultipleinformationprovidersinthesamenetwork,somultiplevideoserversmaybedeployedandusedbythenetworkserviceoperationcenter.Thefunctionoftheservicepopulationismainlytoconnectuserstothecorrespondingserveraccordingtotheservicecontentrequiredbytheusers.Anetworkcanhavemultipleservicepopulations,andoneservicepopulationcanalsoconnectmultipleusers.TheservicepopulationcanbeusedasanindependentnetworkcomponentorintegratedintoothercomponentssuchaslivefrequencyserversorATMswitchingcenters.Theserviceoperationcenterisacomponentusedbyserviceproviderstomanageandallocateinformationresourcesandprovideuserswithrelatedserviceoperations.Ifthenumberofserviceprovidersislarge,theserviceoperationcentercanbeusedasanindependentcomponent;ifthenumberofserviceprovidersissmall,itisgenerallyintegratedintothelivefrequencyserver.Thefunctionofthevideolibraryistostoreinformationfilesintheformofcompressioncoding,andtheaccessdeviceprovidestheconnectionbetweenthenetworkandtheuser.Itisgenerallycomposedofdeviceslocatedbetweenthenetworkandtheuserequipment(CPE).CPEincludestelevisionsandvideorecorders,set-topboxesandremotecontrols.TheATMnetworkinterconnectsvariouspartsofthenetwork,including"signaling"and"programdatastream".Theprogramdatastreamshouldmeettheraterequiredbyusersondemand.Theconnectionmodecanbepoint-to-pointorpoint-to-multipoint.
Transmissionsystem
Thetransmissionsystemiscomposedofatrunktransmissionsystemandadistributionsystem.ThefunctionistosendinformationfromtheVODvideoserverandothersignalsourcestotheuserAndsendbacktheuser'sreverseinformation.Thetrunktransmissionsystemcanhaveopticalfiber,coaxialcableandwirelesstransmissionmethodsforselection;thedistributionsystemhasopticalfiber(FITL),copperwire(ADSL,etc.),hybridfibercoaxialcable(HFC)andwireless(LMDS)andotherimplementationmethods.ThegeneralpracticeofpostandtelecommunicationscompaniesistouseADSL/HDSL/VDSLtechnologytotransmitprogramsinthePSTN;whiletheradioandtelevisiondepartmentsgenerallyuseHFCtechnologytobroadcastprogramsintheCATVsystem.
Intermsoftransmissionrate,real-time,interactivity,economy,etc.,theonlythreecommonnetworksthatcanbeusedasVODsystemuserstoaccessthenetworkarePSTNandCATVsystems.However,boththePSTNandCATVsystemsneedtobeimproved,thePSTNneedstoincreasetherate,andtheCATVsystemneedstoincreasethetwo-waycommunicationcapability.
Userequipment
Userequipmentmainlyhastwotypesofstructures.Thefirsttypeofstructureseparatesthenetworkterminal(NT)fromtheset-topbox.E1/V24interfacesaremostlyusedbetweenthetwo.
Opticalcable2canprovide2Mb/Sdownstreamconnectionsandbidirectionalcontrolconnections.Inthefuture,therewillbeaso-calledstandarddigitalhomenetwork(DHN),whichallowsseveralset-topboxestobeconnectedandcanreuseexistingtwistedpairorcoaxialcablestoprovideabandwidthoftensofmegabitspersecond.ThesecondstructureintegratesNTintoaset-topbox.Thebasicfunctionoftheset-topboxistodecodeMPEGsignalsandinterfacewithordinaryTVsets.Thereareotherfunctionssuchasman-machineinterface,conditionalaccess(encoding),passwordcontrol,smartcardandcreditcardreader.
Set-topboxesalsohavelow-endandhigh-endproducts.Theformerisevolvedfromaset-topboxusedforpayTVdecoding,whichischeaper,buthaslimiteduserinterfaceandprocessingcapabilities.Thelatterevolvedfromaworkstation/PCwithahigh-performanceprocessingplatform,includingatleast4MBofstoragecapacity,andcanprovidegraphicaluserinterfaces,voicerecognition,animationproduction,andgames.
Networkstructuresolution
VariousHUBHFCstructurestakeintoaccounttheexistingcoaxialcableconditionsofthebuildingandsupportexistingandemergingnarrowbandandbroadbandbusiness.
ThesignalfromtheVODvideoserver(155Mb/s)andothertraditionalmultimediasignalssuchasCATVaresenttothecentralpoint(HUb)formodulation,andtheHUbisthedigital/analogconversionintheVODnetworkInterface;theforwardchannelreceivesVODdigitalsignalsandothermultimediasignals,andtransmitsthemtoeachnode(NOde)throughopticalfiber.Thereversechannelreceivesthecontrolsignalfromtheuserside,processesit,andsendsittotheATMswitchandtheVODvideoserver.NodereceivestheforwardRFsignalfromtheHubthroughtheopticalfibertrunk;itisprocessedbythelinearamplifierandtransmittedtotheuserthroughthecoaxialcabledistributionnetwork;NodemustalsofilterouttheRFreversesignalfromtheuseranddriveitthroughthelaserSenditbacktoHUb.
ADSLtechnologycanalsobeusedtoinstallADSLequipmentatfibernodesanduserstoachieveVODservicesandotherbroadbandservices.
ATMswitchandbroadbandsubscriberlooparekeytechnologiesforthedevelopmentofVODservices.TheVODsystemusingATMtechnologycanserveuserswellandhasthesmallestnetworkbandwidthrequirements.ATMswitcheshavebeencommercialized,andthebroadbandizationofusernetworksisoneofthebiggestproblemsindevelopingbroadbandservicessuchasVOD.Opticalfibersubscriberloops(FTTH,FTTC,FTTB,etc.)arethefuturedevelopmentdirectionofbroadbandhigh-speedsubscriberloopsduetotheirbandwidth,high-speeddatatransmissionandevenhigh-definitionTV,andadaptabilitytothedevelopmentofB-ISDNandinformationhighways..However,duetoitslargeinvestment,userscannotaffordit.WeshouldmakefulluseofHFC,ADSLandHDSLtechnologiestotapthepotentialanddevelopbroadbandservicessuchasVOD.
Userinterfacefeatures
VODvideoservermustruncorrespondingsoftwaretocoordinatevariousactions;atthesametimeprovideafriendlyuserinterface.Itshouldhavethefollowingcharacteristics:
(1)Itcanstoreatleastseveralhundredhoursofimageprograms.
(2)Ifauser'srandomdynamicaccesstotheVODserveriscalledasessionprocess,thentheVODservermustbeabletosupportthousandsofsimultaneousandindependent"session"processes.
(3)Ithasasetofencryptionanduseraccesscontrolmechanismtopreventillegaluseraccess.
Asthecoreoftheon-demandsystem,theperformanceoftheVODvideoserverdirectlydeterminestheoverallperformanceofthesystem.Inordertorespondtotheservicerequirementsofmultipleusersatthesametime,thevideoservergenerallyadoptsatimesliceschedulingalgorithm.
Inordertobeabletoadapttoreal-time,continuousandstablevideostreams,thevideoservershouldhavealargestoragecapacityandahighdatarate,andshouldhavemultiplefunctionssuchasadmissioncontrol,requestprocessing,dataretrieval,andstreamtransmission.,Toensurethatusersrequesteffectiveservicesundersystemresources.StoragedevicesshoulduseSCSIinterfacestoensurehigh-speed,parallel,andmultipleI/Obuscapabilities.TheATM-basedVODsystemusesabroadbandvideoserverwithamulti-channelself-routingswitch(MPSR)asthecenter.Theserverwiththisstructurecanprovidetwoservicemodes:InteractiveVODwithInstaneousaccess(IVOD-i)andInteractiveVODwithdelayedaccessIVOD-d.Whenalargenumberofusersareon-demandatthesametime,thetransmissionrateoftheserverisveryhigh;atthesametime,otherrelatedequipmentisrequiredtoalsosupportthishightransmissionrate,whichisdifficulttoachieve.Tothisend,youcansetupavideobufferpoolattheedgeofthenetwork(suchasatthefront-endswitchoftheATMnetwork),andcopyprogramswithahighon-demandratetothebufferpool,sothatsomeusersonlyneedtoaccessthebufferpool,andthereisnothinginthebufferpool.Programscanvisittheserveragain,whichreducestheburdenontheserverandcanincreasethebufferpoolasusersincrease.Theloadingbufferpoolcanbeusedatarateof150Mb/S,andthetransferofprogramsfromthebufferpooltousersisatarateof2Mb/S,sothatoneservercansupportmultipleusers.
Futureplan
Thedevelopmentfromasingleservermodeltoapeer-to-peermodelisaccompaniedbymarketdemand,butevenpeer-to-peermodelsfacechallenges,andthebiggestchallengeisthelackofserviceprovidersThedeliveryofmanagement,thenetworkitselfalsofaceschallenges.Tothisend,weneedacompletelynewsolution-infactamixtureoftheabovethreesolutions.ThisisaworkaroundthatallowsserverunitsinaVODnetworktosharestorageandprocessingresources.ThistechnologyiscalledPeer-AssistedVideo-on-Demand.
P2Pvideoplayback
Point-to-pointauxiliaryvideoondemandissometimescalledMultipleSourceStreamingVOD(MultipleSourceStreamingVOD).Efficientarchitecture.Inamulti-sourcestreamsystem,theoriginalvideostreamisdividedintomultiplevideoblocksandthentransmittedoverthenetwork,similartothefactthatthemessageisdividedintodatapacketsbeforebeingtransmittedovertheIPnetwork.Ifimplementedcorrectly,itcannotonlyimprovefaulttolerance,eliminatebottlenecks,andsignificantlyimprovetheutilizationofavailablebandwidth,butitcanalsosupportagreatlyincreasedplaybackspeed.Forsuccessfulimplementation,amulti-sourcestreamscheduler(MSS)needstobedeployed.MSSreceivesstreamblocksfromdifferentserverssuchasproxyserversorpeer-to-peerservers,sortsthevideoblocksappropriately,andthensendsaseamless,constantblockratevideostreamtotheclientdevice.MSScertainlyfacesitsownchallenges.ChangesindatablocktransmissionwillcausetheMSSbuffertounderflow,whichinturnwillcauseplaybackstarvationandplaybackjitter.Chip-basedalgorithmscanmoreorlesshelpalleviatethisproblem,butensuringpredictable(andbillable)QoSrequiresstrongercontrol.Relyingonmultipleserverstosendvideostreamstoasingleclientatthesametime,thisarchitecturehasmanyadvantages.Notonlyisithighlyfault-tolerant,butitcanalsoredirecttheservicestreamasneeded,therebyavoidingnetworkhardwarefailuresorcongestionthataffectsservices.Inaddition,thearchitecturealsosupportshigh-resolutionvideotransmissionandsimultaneoussessionsofmultiplevideostreams.Thismodelalsoallowsredundantdatatobesentasafailurepreventivemeasure,therebyimprovingtheoverallqualityofservice.
Inshort,VODwasdevelopedinthe1990s.WiththepopularizationofglobalIPTVequipment,thecontinuousenrichmentofplayablemoviecontent,thecontinuousupdateofelectronicproductswithIPconnectivity,andthedevelopmentofthemobileTVmarketWithcontinuedgrowth,VODwillalsousherinaperiodofrapidgrowth.The2008OlympicGamespromotedtherapidgrowthofP2Pvideoplaybackplatforms.Point-to-pointnetworksarebecomingthemainvideodistributionmechanisminIPnetworks,andthegradualintegrationoftechnicalelementsinmodernVODnetworksisalsoreducingnetworkandservicedeliverycosts,improvingbandwidthutilizationefficiencyandimprovingQoSlevels.Facingthevastmarketofvideo-on-demand,bothequipmentsuppliersandserviceproviderswillbeaneraofbothopportunitiesandchallenges.