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Protocol overview

A data transfer protocol is a standardized format for transmitting data between two devices. The type of protocol used can determine such variables as the error checking method, the data compression method, and end-of-file acknowledgements. If all networks were constructed in the same manner and all networking software and equipment behaved similarly, only one protocol would be necessary to handle all of our data transmission needs. In reality, the Internet is comprised of millions of different networks running a wide array of hardware and software combinations. As a result, the ability to stream digital media content reliably to clients depends on a set of several well-engineered protocols. The protocols used to stream Windows Media-based content are:

Windows Media Services manages the use of these protocols by using control protocol plug-ins. Windows Media Services includes the WMS MMS Control Protocol plug-in, the WMS RTSP Control Protocol plug-in, and the WMS HTTP Control Protocol plug-in. With the exception of the WMS HTTP Control Protocol plug-in, these plug-ins are enabled by default.

The control protocol plug-in receives the incoming client request, determines what action is indicated by the request (for example, to start or stop streaming), translates the request into a command form, and then passes the command to the server. Control protocol plug-ins can also return notification information to clients if there is an error condition or a change of status.

While the previously listed protocol plug-ins listed handle the high-level exchange of data, basic networking protocols such as User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) are used to manage more fundamental tasks such as network connectivity and packet error correction. The MMS and RTSP protocols are used in combination with both the UDP or TCP protocols.

The following diagram depicts how Windows Media Services uses different protocols to negotiate connections between a Windows Media server, encoders, content sources, and clients.

Protocol overview

Windows Media Services 9 Series in Windows Server 2003, Enterprise Edition or in Windows Server 2003, Datacenter Edition includes the following additional networking capabilities:

Clients that receive content as a multicast stream do not use a connection-based protocol. Instead, they receive the stream by joining to a multicast broadcast. The information the client needs to locate and join a multicast stream is contained in a multicast information file with an .nsc file name extension. The client first opens the file from a Web server or from a link in an e-mail and then uses the information contained in the file to connect to the multicast stream.

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