外文翻译--标准式多播广播站.doc

论文附件一、英文原文UnderstandingmulticaststationsAstationisusedtomulticastanASFstreamtoaclient,specificallyMicrosoftWindowsMediaPlayer.Multicastingminimizesthenetworkbandwidthused.IfclientsdonotusethestationtoreceivetheASFstream,theneachclientrequiresitsownconnectiontoaserver.Thisquicklyconsumesnetworkbandwidthandlimitstheabilityofthenetworktodeliverinformation.Distributionmodeisastationcharacteristicthatdefineswhetherastationistobeusedformulticasting,distribution,orboth.MulticaststationsdeliverASFstreamstomanyclientsbutuseonlythebandwidthofasinglestream.DistributionstationsdeliverASFstreamstootherWindowsMediaserversviaunicast.AstationthatissolelyadistributionstationdoesnothaveanIPaddressorport,soclientscannotviewthestreamthatthestationdelivers.StationsenabledformulticastanddistributiondeliverASFstreamstootherWindowsMediaserversviaunicast.ClientscanalsoviewtheASFcontentonthisstationviamulticast.AstationcontainsalltheinformationneededtodeliveranASFstreamtoWindowsMediaPlayer,includingIPaddress,port,streamformat,time-to-live(TTL)value,andsoon.Thisinformationisstoredinan.nscfile.WindowsMediaPlayermustbeabletoaccessthe.nscfilesothatitcanlocatetheIPaddressthatthestationisusingtostreamASFcontent.The.nscfileistypicallymadeavailabletoWindowsMediaPlayerfromasharednetworkdirectoryorfromaWebserverdirectory.WindowsMediaPlayerextractstheURLtothe.nscfilewhenitopensanannouncementthatisdeliveredtoitinanemailmessage,viaUNCpath,orfromaWebpagelink.TheMulticastStationspageinWindowsMediaAdministratoristheaccesspointforcreatingandmanagingstations.Thispagealsoprovidesaninterfacefororganizingstreamsintotheprogramsdeliveredonthestationsyoucreate.UnderstandingdistributionstationsAdistributionstationisahelperstation.ItdeliversanASFstreamfromWindowsMediaserverAtoastationonWindowsMediaserverBsothatWindowsMediaserverBcanmulticastthatASFcontent.Adistributionstationprovidesawayto:Distributeastreambetweennetworksegmentsthatarenotconnectedbymulticast-enabledrouters.Distributeastreampastafirewall.Otherstationsaccessthedistributionstationbycreatingaconnectiontothedistributionstation.nscfileusingtheMSBDprotocol.Forexample,ifyouwantStation2onServerBtomulticasttheASFcontentfromdistributionstation,Station1onServerA,youuseStation1asthestreamsource.Thatis,thestreamsourceforStation2ismsbd:/ServerA/Station1.NoteWhenyoudistributestreamsbetweenservers,youmustnotexceedthedistributionlimit,thenumberofMSBDconnectionsthatadistributionstationcanaccommodate.Bydefault,adistributionstationcansupportonlyfiveMSBDconnectionstootherstations.AsyouconfigurestationsonremoteWindowsMediaserverstouseadistributedASFstream,youmustadjustthedistributionstationDistributionLimittoaccommodatetheadditionalremoteconnections,orusemorethanonedistributionstationasthesourcefortheremotestation.FormoreinformationaboutadjustingtheDistributionLimit,seeEditingstationproperties.Deliveringstreamsoveranon-multicast-enablednetworkIfyournetworkdoesnotusemulticastrouters,youcanmulticastastreamonlywithinthenetworksegmentthatcontainsWindowsMediaservercomponents.ClientsonothersegmentsofthenetworkcannotreceivetheASFstreammulticastbecauseitdoesnotoriginatewithintheirsegment.ClientsthroughoutthenetworkcanstillreceivethestreamiftheASFcontentismulticastwithinthelocalsegment,anddistributedtoWindowsMediaserversontheothernetworksegments.Thestationonthelocalnetworksegmentmusthavebothmulticastanddistributioncapabilitiestoaccomplishthis.Fortheothernetworksegmentsonwhichyouwanttoenablemulticaststreaming,youmustinstallaseparatecomputerrunningWindowsMediaservercomponents.OneachWindowsMediaserver,useStationQuickStartwizardtocreateastationwithmulticastcapabilitiesthatusestheremotedistributionstationasthestreamsource.EachoftheseWindowsMediaserversthencanmulticasttheASFstreamwithinitslocalsegment.NoteThestreamformatthatwasspecifiedintheremotedistributionstationmustbeusedforthemulticaststationscreatedineachnetworksegment.Formoreinformation,seeImportingastation.DeliveringstreamsthroughafirewallIfyoudonothaveaWebserver,butwanttostreamcontentacrossafirewalltoaclient,youcanenableHTTPstreamingonWindowsMediaservercomponents.HTTPstreamingisusefulfordeliveringastreamthroughafirewallbecauseHTTPstreamingusuallyusesport80andmostfirewallsdonotblockport80.WindowsMediaservercomponentscontainstwostreamingservicesWindowsMediaStationserviceandWindowsMediaUnicastservice.WindowsMediaservercomponentscanbeconfiguredtouseHTTPstreaming,butonlyonestreamingservice(WindowsMediaStationserviceorWindowsMediaUnicastservice)canuseHTTPstreamingatatime.Thisisbecauseonlyoneservicecanbindtoport80.IfyouenableaWindowsMediastreamingservicetostreamusingHTTP,youcannotrunanotherHTTPserveronthesamecomputerbecausetheWindowsMediastreamingserviceandtheHTTPservicecompeteforuseofport80.ItispossibletoconfigureHTTPstreamingtouseadifferentport,allowingWindowsMediaservercomponentsandanotherHTTPservice(forexample,MicrosoftInternetInformationServerIIS)torunonthesamecomputer.Theonlydrawbackisthatmostfirewalls,bydefault,onlyallowHTTPtraffictopassthroughport80.Therefore,thisfunctionalityisgenerallyreservedforserver-to-serverdistribution,reservingport80fordirectserver-to-clientconnections.FormoreinformationaboutconfiguringHTTPstreamingtouseadifferentport,seeUsingHTTPstreaming.CreatingmulticaststationswithWindowsMediaAdministratorYoucancreateamulticaststation,adistributionstation,orastationformulticastanddistributionusingtheConfigureandPublishMulticastBroadcastStreamsQuickStartwizardontheMulticastStationspageinWindowsMediaAdministrator,oryoucanuseanadvancedmethodtocreateoneofthesestations.Ifyouusethewizardtocreateoneofthesestations,streamformatinformationisaddedtothestationdefinitionontheSpecifystreamformatinformationscreen.Ifyouusetheadvancedmethodtocreateastation,itispossibletocreatethestationwithoutaddingstreamformatinformationtothestationdefinition,andtheWindowsMediaserverwillplaytheprogramforthisstation.Ifyoucreateadistributionstation,otherstationscanreceivethestreamfordistributionbecausestreamformatinformationisnotrequiredtodistributeastream.However,ifyoucreateamulticaststation,multicastclientscannotconnecttothestationbecauseallstreamformatinformationismissing.Toenablethemulticastclientstorenderthemulticaststreamforthe