Microsoft Media Services
The MMS protocol (Microsoft Media Server Protocol) is a Microsoft protocol of the application layer, which is used for transmitting multimedia streams.
Terms
The acronym MMS stands for Microsoft Media Server. The protocol was therefore named after the associated server software whose full name Microsoft Windows Media Server and is part of the software package Windows Media Services (formerly Microsoft NetShow Services). As client software typically the Windows Media Player will be used. In summary, we speak of the so-called Windows Media Technologies. The computer on which the server software is running, ie streaming media server.
Generating an MMS session
The MMS protocol is initiated by a client who wants to process a URL with the prefix " mms :/ /". He first establishes a TCP connection to port 1755 of the server to transmit its IP address and a self-selected UDP port. The server then generates a UDP socket and connects it to the desired port of the client. The transmission of the multimedia data takes place via these UDP connection ( MMSU ), while the TCP connection is used for control commands. It is possible however, that the UDP connection is prevented by a firewall. In this case, the client can also request transmission of the multimedia data relied on for this purpose, however, less suitable TCP connection ( MMSE ). If that fails, the third option must be used when the communication is over HTTP. This process, in which the appropriate protocol version is negotiated, also referred to as "protocol rollover ". Due to the improved real-time properties, the MMSU variant is always preferred, and there is also the possibility to request lost packets, if enough time is available. The first MMS packets at session set contain at offset = 12 The identifier "MMS".
Windows Media formats
- The " Advanced Streaming Format" (. Asf) is required for the multimedia data file format. This can be a stream to be kept in different compression ratios, resulting in better bandwidth adjustment is enabled.
- The " Advanced Stream Redirector metafiles " (. Asx ) allow hyperlinks to streams and the specification multipart content, ie realize playlists. They also contain rules for the "protocol rollover " mechanism.
- The "Microsoft Windows Media metafiles station " (. Nsc ) are used to support multicasting, and describe a kind of channel on which the client can access similar to a television channel.
Adjustment range
The client agrees to the server first on a quality level of transmission that matches the available bandwidth. This requires the use of an ASF file that holds the stream encoded at different data rates. Later, if the bandwidth decreases, the client can also thin out the stream dynamically, with a continuous adaptation of "full frames" down to "key -frame only " is possible. When in such a reduced bandwidth always the sound then has the priority over the image. The bandwidth conditions improve then, the video bit rate can be increased again to the optimum. These possibilities to adapt the data stream to a variable bandwidth are grouped under the term "Smart Streaming ".
Unicast and multicast
If the server in unicast mode operated, then for each recipient its own connection needed, and the data must be sent each time again. The client can then the data stream " on-demand" received, ie, has control over the playback operation (eg start, stop, pause or search), similar to a VCR. Multicasting other hand, means that many recipients can receive the data stream once sent simultaneously. For this, the network must be multicast -enabled and the server in multicast mode to operate. One speaks in this case of broadcast channels, similar to the reception of a television program, that is, the recipient can not control the playback. The advantage is then in a much lower load on the network.
HTTP streaming
When HTTP streaming the URL prefix may likewise " mms :/ / " loud, but it is in contrast to the MMS streaming described in this article to a fundamentally different technology, in which, instead of the "Windows Media technologies" HTTP and an HTTP Server that has been extended by some features to get better real-time properties. But this is not to be confused with the above described method of the MMS streaming over HTTP.
Download
Normally, the permanent storage of multimedia files received via the MMS protocol is not possible nor desirable, therefore, the exact specification of the MMS protocol has also been a long time Microsoft kept secret (Publication of protocol specification on 8 February 2008, news item SDP Multimedia on March 27, 2008). Nevertheless, and some other such as Nettransport or the player VLC exist alongside the SDP Downloader various free programs that allow the saving of streams is possible.
Swell
- Protocol Specification
- Streaming media server role: Configuring a streaming media server
- Windows Media Technologies Application Development
- Firewall and NAT Support for Streaming over MMS