8.2.3 Microsoft Media Server Protocol
The Microsoft Media Server (MMS) Protocol is used to transfer real-time multimedia data (for example, audio and video). Because it is a streaming protocol, the MMS Protocol attempts to facilitate scenarios in which the multimedia data is being transferred and rendered (such as video displayed and audio played) simultaneously.
The MMS Protocol is suitable for streaming delivery of real-time multimedia data. The term streaming means that data is transmitted at some fixed rate, or at some rate related to the rate at which the data is consumed (for example, displayed) by the receiver.
It is appropriate to use this protocol when a client is streaming from a server that does not support the RTSP Windows Media Extensions or Windows Media HTTP Streaming Protocol. Otherwise, use of the MMS Protocol is generally not appropriate.
If MMS is used in a scenario in which the multimedia data is always transferred over TCP, the Windows Media HTTP Streaming Protocol might be more appropriate to use instead because it does not include the UDP functionality.
The MMS Protocol uses a TCP connection for control of the streaming media session. The entity that initiates the TCP connection is referred to as the client, and the entity that responds to the TCP connection is referred to as the server. The multimedia data flows from the server to the client.
The client can send MMS Protocol request messages to the server over the TCP connection, to request the server to perform actions such as starting and stopping the flow of multimedia data. The multimedia data is transferred either over the same TCP connection or as a flow of UDP packets.
While the server is transmitting multimedia data to the client, the client can send MMS Protocol messages to the server, requesting that it change the stream being transmitted. For example, the client can request that the server replace the currently transmitted video stream with a lower bit-rate version of the same video stream.
If UDP is used to transmit the multimedia data to the client, the client can send an MMS Protocol message to the server requesting that it resend a UDP packet. This approach is useful if the client does not receive a UDP packet the server transmitted. Unlike other MMS Protocol messages sent by the client, the request to resend a UDP packet is sent using UDP.
Streaming media content may be made accessible only to authorized clients. The authentication sequences that the MMS Protocol supports are based on a basic and new technology local area network (NT LAN) Manager (NTLM) sequence. Authentication is not covered in detail as part of this task overview. See the Authentication Services overview for more information on authentication protocols.