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1、论文附件一、英文原文Understanding multicast stationsA station is used to multicast an ASF stream to a client, specifically Microsoft Windows Media Player. Multicasting minimizes the network bandwidth used. If clients do not use the station to receive the ASF stream, then each client requires its own connectio

2、n to a server. This quickly consumes network bandwidth and limits the ability of the network to deliver information.Distribution mode is a station characteristic that defines whether a station is to be used for multicasting, distribution, or both.Multicast stations deliver ASF streams to many client

3、s but use only the bandwidth of a single stream.Distribution stations deliver ASF streams to other Windows Media servers via unicast. A station that is solely a distribution station does not have an IP address or port, so clients cannot view the stream that the station delivers.Stations enabled for

4、multicast and distribution deliver ASF streams to other Windows Media servers via unicast. Clients can also view the ASF content on this station via multicast.A station contains all the information needed to deliver an ASF stream to Windows Media Player, including IP address, port, stream format, ti

5、me-to-live (TTL) value, and so on. This information is stored in an .nsc file.Windows Media Player must be able to access the .nsc file so that it can locate the IP address that the station is using to stream ASF content. The .nsc file is typically made available to Windows Media Player from a share

6、d network directory or from a Web server directory. Windows Media Player extracts the URL to the .nsc file when it opens an announcement that is delivered to it in an email message, via UNC path, or from a Web page link.The Multicast Stations page in Windows Media Administrator is the access point f

7、or creating and managing stations. This page also provides an interface for organizing streams into the programs delivered on the stations you create.Understanding distribution stationsA distribution station is a helper station. It delivers an ASF stream from Windows Media server A to a station on W

8、indows Media server B so that Windows Media server B can multicast that ASF content. A distribution station provides a way to:Distribute a stream between network segments that are not connected by multicast-enabled routers.Distribute a stream past a firewall.Other stations access the distribution st

9、ation by creating a connection to the distribution station .nsc file using the MSBD protocol. For example, if you want Station2 on ServerB to multicast the ASF content from distribution station, Station1 on ServerA, you use Station1 as the stream source. That is, the stream source for Station2 is ms

10、bd:/ServerA/Station1.NoteWhen you distribute streams between servers, you must not exceed the distribution limit, the number of MSBD connections that a distribution station can accommodate. By default, a distribution station can support only five MSBD connections to other stations. As you configure

11、stations on remote Windows Media servers to use a distributed ASF stream, you must adjust the distribution station Distribution Limit to accommodate the additional remote connections, or use more than one distribution station as the source for the remote station. For more information about adjusting

12、 the Distribution Limit, see Editing station properties.Delivering streams over a non-multicast-enabled networkIf your network does not use multicast routers, you can multicast a stream only within the network segment that contains Windows Media server components. Clients on other segments of the ne

13、twork cannot receive the ASF stream multicast because it does not originate within their segment.Clients throughout the network can still receive the stream if the ASF content is multicast within the local segment, and distributed to Windows Media servers on the other network segments. The station o

14、n the local network segment must have both multicast and distribution capabilities to accomplish this.For the other network segments on which you want to enable multicast streaming, you must install a separate computer running Windows Media server components. On each Windows Media server, use Statio

15、n QuickStart wizard to create a station with multicast capabilities that uses the remote distribution station as the stream source. Each of these Windows Media servers then can multicast the ASF stream within its local segment.NoteThe stream format that was specified in the remote distribution stati

16、on must be used for the multicast stations created in each network segment. For more information, see Importing a station.Delivering streams through a firewallIf you do not have a Web server, but want to stream content across a firewall to a client, you can enable HTTP streaming on Windows Media ser

17、ver components. HTTP streaming is useful for delivering a stream through a firewall because HTTP streaming usually uses port 80 and most firewalls do not block port 80.Windows Media server components contains two streaming servicesWindows Media Station service and Windows Media Unicast service. Wind

18、ows Media server components can be configured to use HTTP streaming, but only one streaming service (Windows Media Station service or Windows Media Unicast service) can use HTTP streaming at a time. This is because only one service can bind to port 80.If you enable a Windows Media streaming service

19、to stream using HTTP, you cannot run another HTTP server on the same computer because the Windows Media streaming service and the HTTP service compete for use of port 80.It is possible to configure HTTP streaming to use a different port, allowing Windows Media server components and another HTTP serv

20、ice (for example, Microsoft Internet Information Server IIS) to run on the same computer. The only drawback is that most firewalls, by default, only allow HTTP traffic to pass through port 80.Therefore, this functionality is generally reserved for server-to-server distribution, reserving port 80 for

21、 direct server-to-client connections. For more information about configuring HTTP streaming to use a different port, see Using HTTP streaming.Creating multicast stations with Windows Media AdministratorYou can create a multicast station, a distribution station, or a station for multicast and distrib

22、ution using the Configure and Publish Multicast Broadcast Streams QuickStart wizard on the Multicast Stations page in Windows Media Administrator, or you can use an advanced method to create one of these stations. If you use the wizard to create one of these stations, stream format information is ad

23、ded to the station definition on the Specify stream format information screen.If you use the advanced method to create a station, it is possible to create the station without adding stream format information to the station definition, and the Windows Media server will play the program for this stati

24、on. If you create a distribution station, other stations can receive the stream for distribution because stream format information is not required to distribute a stream. However, if you create a multicast station, multicast clients cannot connect to the station because all stream format information

25、 is missing.To enable the multicast clients to render the multicast stream for the station, you must add stream format information for all of the streams in the program to the multicast station definition. If you do not add stream format information for all the streams in the program to the multicas

26、t station program definition, then the Windows Media server will not deliver the streams in the playlist for which stream format information was not added and will report the error, The station does not support the stream format in the status report for these streams on the Multicast Stations page.I

27、f you create a station enabled for multicast and distribution, and you do not add the stream format information for all the streams in the program to the station definition, both multicast clients and distribution stations receive only the streams in the playlist for which stream format information

28、is included in the station definition and fail to receive the rest of the streams.For more information, see Adding stream format information.Selecting stream sources for stationsWhen you create a station, you must provide the source URL and stream format information for the content that you are stre

29、aming. This content can be an .asf file, an .mp3 file, a stream from a Windows Media Encoder, a remote station, or a remote broadcast publishing point. The source URL is provided on the Specify a source URL for the stream object page in Configure and Publish Multicast Broadcast Streams QuickStart wi

30、zard. Next, the stream format information in provided on the Specify stream format information screen in the wizard.Adding stream format informationMicrosoft Windows Media Player uses stream formats to decode a multicast ASF stream. Stream formats are stored in the station .nsc file and can be downl

31、oaded to Windows Media Player. A stream format includes information about the stream, the media that the stream contains, and its codec. A stream format is required for every type of stream that plays through a station. If two or more stream objects are defined for a station and are using different

32、codecs, bit rates, or frame sizes for the streams, then stream format information must be specified for both types of streams. If stream format information is either missing or incorrect for a stream in the program for a station, Windows Media Player either cannot start the stream or cannot play som

33、e of the streams in the program playlist. For more information, see Creating multicast stations with Windows Media Administrator.If you use the Configure and Publish Multicast Broadcast Streams QuickStart wizard on the Multicast Stations page in Windows Media Administrator to create a station, strea

34、m format information is added to the station definition on the Specify stream format information screen.If you are using the advanced method to create a station or if you are adding streams to an existing station, you must add stream format information to the station definition. For more information

35、, see Editing station properties.Creating unicast rollover for a multicast stationUnicast rollover can be used when Microsoft Windows Media Player cannot receive multicast packets from a station. This can occur, for example, because the network routers are not multicast-enabled, or because Windows M

36、edia Player is beyond the time-to-live (TTL) radius of the multicast. Unicast rollover will not occur when a multicast station streams no content because a multicast station emits beacon packets even if no program is defined for it. If Windows Media Player is within the TTL radius of the multicast,

37、it binds to the beacon packets, which contain no content.When Microsoft Windows Media Player opens an .asx file for a multicast station, the .asx file instructs Windows Media Player to download the .nsc file, which can contain a unicast rollover URL. If Windows Media Player cannot receive the ASF st

38、ream that is being multicast, it uses the unicast rollover URL to connect to the server and receive the stream from a broadcast unicast publishing point.If you use Configure and Publish Multicast Broadcast Streams QuickStart wizard to create a station for multicast and distribution, the wizard creat

39、es a broadcast unicast publishing point (with an alias that is identical to the station name) that references the station. The wizard adds a unicast rollover URL to this broadcast unicast publishing point in the station definition.If you use the wizard to create a multicast station, or if you use th

40、e advanced method to create a station for multicast and distribution or a multicast station, and you want to enable unicast rollover for your station, you must create a broadcast unicast publishing point that uses the multicast station as the stream source. For more information, see Using broadcast

41、unicast publishing points. Then to enable unicast rollover for the station, you must supply a unicast URL to the broadcast unicast publishing point in the form mms:/server_name/alias, where server_name is the name of the server that hosts the broadcast unicast publishing point and alias is the broad

42、cast unicast publishing point alias. For more information, see Editing station properties.Publishing station contentWhen you choose a publishing method, the wizard creates that .htm file or copies that HTML code to the Microsoft Windows clipboard, so that you can paste the code into an HTML page. An

43、 .asx file that points to the ASF stream is created by default; the following publishing methods provide the Web syntax that links to the .asx file.Create an .htm file with an to the .asx fileStation QuickStart wizard prompts you for a location in which to save the .htm file, and to rename it if nec

44、essary. To make this file available to others, save it on a Web server. The default name of the .htm file is station_name.To test the Web page created by this file, click Test .htm w/ HREF on the last screen of the wizard to open the sample Web page, which contains the link to the .asx file. Click t

45、he link to open Microsoft Windows Media Player. Windows Media Player accesses the station and plays the stream.Create an .htm file containing and tags for Windows Media PlayerStation QuickStart wizard prompts you for a location in which to save the .htm file, and to rename it if necessary. To make t

46、his file available to others, save it on a Web server. The default name of the .htm file is station_name_object_tag.To test the Web page created by this file, click Test .htm w/ OBJECT on the last screen of the wizard to open the Web page in the browser. When the Web page opens, the Windows Media Pl

47、ayer control appears. Windows Media Player automatically accesses the station and plays the stream.Copy syntax to the Windows clipboardThis option inserts the name of and path to your .asx file in the code that creates a link to your station content. Paste this HTML code from Windows clipboard into

48、any Web page to create a link to your station.Copy and syntax to the Windows clipboardThis option inserts the name of the .asx file and the path to the .asx file into the code that embeds the Windows Media Player control. Paste this HTML code from the Windows clipboard into any Web page so that your

49、 station content is played automatically when the Web page is opened.Editing station propertiesThe New Station page lets you enter individual station properties to create a station without using Station QuickStart wizard. The Edit Station page lets you view and edit the properties of an existing sta

50、tion. These two pages are identical, except that the property boxes in the New Station page are empty.The station properties are described in the following table. The Name, Port, and Station File Path properties are required; you cannot create an .nsc file without filling in these boxes. The other p

51、roperties are optional.Setting multicast destination IP address and portA multicast program is directed to its destination by the station IP address and port. Clients receive the multicast program by instructing their network cards to listen for packets arriving at that IP address and port.For ASF c

52、ontent, the destination IP address and port are set when you create the station in Windows Media Administrator using the Stations page. Clients learn which address and port to listen to by downloading the .nsc file.You can create multiple programs destined for the same IP address; however, you must

53、avoid multicasting programs to the same IP address simultaneously. For example, sending a file to the same destination as an audio multicast can interfere with the audio stream.NoteFor file transfer streams, the destination IP address and port are set for each stream in a program when you add stream

54、s using the Multicast File Transfers page in Windows Media Administrator. In order for a client to receive the multicasts, the IP address and port you set for the file transfer stream must match the IP address and port specified by the client network card. For more information, see Configuring a mul

55、ticast file transfer.Setting multicast scopeYou can limit the reach of a multicast to the immediate subnetwork or expand the scope to the entire Internet. The scope is set by specifying a time-to-live. This value, sometimes called the number of hops, decreases each time the multicast passes through

56、a network router. When the value reaches 1, the router stops forwarding the multicast. Values can range from 1 through 255.Windows Media Services provides the following default values for scope.Because the number and configuration of routers in a network actually determine the value that must be use

57、d to limit the scope, you can set a custom value. Your network administrator can determine the value to use to limit the scope to your intranet.Exporting a stationExporting a station saves the station information as an .nsc file in a shared directory or Web directory that Microsoft Windows Media Pla

58、yer can access.The .nsc file contains all the information that Windows Media Player needs to find and render the ASF stream. Typically, the player downloads this file from an HTTP server or a network share by opening an .asx file in email, on a Web page, or from a shared directory. The .asx file poi

59、nts to the .nsc file, which is downloaded to the client computer. Users must have at least read-access to any .nsc files stored on a network share.Importing a stationImporting a station is the easiest way to make sure that the server can distribute a station. If you are setting up Windows Media serv

60、er components to multicast streams that originate from a Windows Media distribution server, the stations you use to multicast must contain identical stream format information. Depending on your network configuration, the stations can use the same destination IP address and port for the multicastfor