【正文】 s Media Player extracts the URL to the .nsc file when it opens an announcement that is delivered to it in an message, via UNC path, or from a Web page link.The Multicast Stations page in Windows Media Administrator is the access point for 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 Windows Media server B so that Windows Media server B can multicast that ASF content. A distribution station provides a way to: Distribute a stream past a firewall.Other stations access the distribution station 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 msbd://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 acmodate. By default, a distribution station can support only five MSBD connections to other stations. As you configure stations on remote Windows Media servers to use a distributed ASF stream, you must adjust the distribution station Distribution Limit to acmodate the additional remote connections, or use more than one distribution station as the source for the remote station. For more information about adjusting the Distribution Limit, see Editing station properties.Delivering streams over a nonmulticastenabled networkIf your network does not use multicast routers, you can multicast a stream only within the network segment that contains Windows Media server ponents. Clients on other segments of the network 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 on the local network segment must have both multicast and distribution capabilities to acplish this.For the other network segments on which you want to enable multicast streaming, you must install a separate puter running Windows Media server ponents. On each Windows Media server, use Station 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 station 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 server ponents. 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 ponents contains two streaming services—Windows Media Station service and Windows Media Unicast service. Windows Media server ponents 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 to stream using HTTP, you cannot run another HTTP server on the same puter because the Windows Media streaming service and the HTTP service pete for use of port 80.It is possible to configure HTTP streaming to use a different port, allowing Windows Media server ponents and another HTTP service (for example, Microsoft Internet Information Server [IIS]) to run on the same puter. The only drawback is that most firewalls, by default, only allow HTTP traffic to pass through port , this functionality is generally reserved for servertoserver distribution, reserving port 80 for direct servertoclient 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 distribution 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 added 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 station. 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 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 multicast station program definition, then the Windows Media server will not deliver the streams in the playlist fo