Protocol Rollover
If a Windows Media Player cannot connect to the URL requested by an end user, it can roll over to a different protocol and try again. Windows Media Player versions 6.4 through 8.0 can switch between the MMSU, MMST, and HTTP protocols. Windows Media Player 9 Series can switch between RTSPU, RTSPT, and HTTP.
A Windows Media cache proxy server can also roll over to different protocols. Proxy plug-ins specify the rollover policy for a cache proxy server, and you can implement a custom rollover policy by creating a custom cache proxy plug-in. For example, assume that a Windows Media Player connects to a Windows Media server acting as a proxy and requests rtspu://origin_server/Audio.wma. Assume also that the cache proxy plug-in specifies that the server can roll over from RTSPU to RTSPT, and from RTSPT to HTTP. Therefore, if the proxy server cannot use the RTSPU protocol to connect to the origin server, it tries to connect to rtspt://origin_server/Audio.wma. If that URL also fails, the proxy server tries http://origin_server/Audio.wma. If all protocols fail, the server disconnects the client. However, if one of the protocols succeeds, it is recommended that your plug-in remember that protocol and try it first the next time a client attempts to connect to the URL. For more information about protocol rollover, see Overview of the Cache Proxy Process.
Note
Your plug-in must specify either RTSP or HTTP to connect to an upstream Windows Media server. It cannot use MMS.