The ability of Windows Media Services to choose the right protocol for a client depending on its environment is known as protocol rollover. Protocol rollover is useful if you are supporting a variety of client versions, clients that are connecting through a firewall, or clients that are connecting through different types of networks. Protocol rollover works best if all the server control protocol plug-ins available on your server (including the WMS HTTP Server Control plug-in) are enabled.
The Windows Media server uses protocol rollover in order to establish the optimal connection to the client. When a client attempts to connect to a server, it sends information about its type and what protocols it can support. The Windows Media server compares that information to the protocols that are enabled and then uses the best protocol for the situation. Typically, the first connection attempt between the server and the client is successful and no further action is taken. If that connection request is not successful, the client attempts to connect to the server using another supported protocol. The client experiences a very small, usually unnoticeable period of latency during each protocol rollover attempt.
In addition, when a client attempts to establish a new
connection to the server, preference is given to the protocol that
the client used in the previous connection. If you use an
It is recommended that you use protocol rollover to ensure that your clients have the optimal streaming experience. If clients connect to your stream using a URL with an mms:// prefix, protocol rollover will occur if necessary. Be aware that users can disable protocols in the property settings of their players. If the player only supports a single protocol, rollover cannot occur. The logic used with protocol rollover differs depending on the type of client connecting to the server.
Windows Media Player 9 Series or later
When Windows Media Player 9 Series or later or a player that uses the Windows Media Player 9 Series ActiveX control attempts to connect to the server using a URL with an mms:// prefix, the server automatically uses RTSP. If Fast Cache is enabled on the server (the default condition for all new publishing points), the server tries to connect to the client using RTSP with TCP-based transport (RTSPT) first. If the Player does not support that protocol, then the server attempts to connect using RTSP with UDP-based transport (RTSPU). If that connection is also not successful, the server will attempt to connect using the HTTP protocol if the WMS HTTP Server Control Protocol plug-in is enabled. If Fast Cache is not enabled, the server first tries to connect to the client using RTSPU, then RTSPT, and finally HTTP.
Earlier versions of Windows Media Player, such as Windows Media Player for Windows XP, do not support the RTSP protocol. However, the MMS protocol provides protocol rollover support for those players. Thus, when an earlier version of the Player attempts to connect to the server using a URL with an mms:// prefix, the server automatically negotiates the best protocol for the Player. The server first tries to connect to the client using MMS with UDP-based transport (MMSU). If that protocol is not supported, then the server attempts to connect using MMS with TCP-based transport (MMST). If that connection is also not successful, the server will attempt to connect using the HTTP protocol if the WMS HTTP Server Control Protocol plug-in is enabled.
Protocol rollover is not used when a distribution server attempts to connect to an origin server. Distribution servers cannot use a URL with an mms:// prefix to request a connection to the origin server. If the distribution server attempts to connect using RTSP, that request is translated as RTSPU. If TCP-based transport is preferred or required, then the URL must use an rtspt:// prefix. If the servers must connect using HTTP, then the URL must use an http:// prefix.