About protocol rollover
Updated: October 4, 2007
Applies To: Windows Server 2008, Windows Server 2008 R2
The ability of Windows Media Services to deliver content to Windows Media Player by using the correct protocol is known as protocol rollover. Protocol rollover is useful if you are supporting a variety of Player versions, Players that connect through a firewall, or Players that connect 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 Player uses protocol rollover to establish the optimal connection to the server. When a Player tries 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 Player and the server is successful and no further action is taken. If that connection request is not successful, the Player tries to connect to the server using another protocol that it supports. The Player experiences a very small, usually unnoticeable period of latency during each protocol rollover attempt.
The logic used with protocol rollover differs depending on the Player version:
Windows Media Player 9 Series or later. When the Player tries to connect to the server using a Microsoft Media Server (MMS) URL moniker (mms://) in the connection URL to your streaming content (for example, mms:// ServerName/FileName.wma), the server automatically delivers the content by using RTSP. If Fast Cache is enabled on the server (the default condition for all new publishing points), the server tries to deliver the content using RTSP with TCP-based transport (RTSPT) first. If the Player does not support that protocol, then the server tries to deliver the content using RTSP with UDP-based transport (RTSPU). If that connection is also not successful, the server will try to deliver the content by 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 deliver the content to the client by using RTSPU, then RTSPT, and finally HTTP.
Earlier players. When an earlier version of the Player, such as Windows Media Player for Windows XP, tries to connect to the server using a URL with an mms:// prefix, the server automatically tries to deliver the content by using the HTTP protocol, if the WMS HTTP Server Control Protocol plug-in is enabled.
To support the widest range of streaming Player versions, you should use the MMS URL moniker (mms://) in the connection URL to your streaming content. The MMS URL moniker allows all connecting Players to use protocol rollover to stream the content using the optimal streaming protocol. If you use an announcement to enable the Player to access your content, the MMS URL moniker is used automatically, ensuring that protocol rollover will occur if necessary. Be aware that users can disable protocols in the property settings of the Player. If the Player only supports a single protocol, rollover cannot occur. Also, be sure to open ports on your firewall for any data transfer protocol that might be selected during protocol rollover (either RTSP or HTTP).
In some cases, a Player that does not support MMS streaming (such as Windows Media Player 12) may be unable to stream your content for one of the following reasons:
The Player successfully selected an alternate streaming protocol during protocol rollover, but the Windows Media server that is hosting your content does not have the control protocol plug-in for the selected streaming protocol (either RTSP or HTTP) enabled. Note that the WMS HTTP Server Control Protocol plug-in that manages HTTP streaming is disabled by default in Windows Media Services.
The Player successfully selected an alternate streaming protocol during protocol rollover, but the Windows Media server cannot deliver the content through your firewall.
The Player cannot use protocol rollover to select an alternate streaming protocol because streaming protocols and proxy settings are not configured correctly on the Network tab in the Player.
The MMS streaming protocol was deprecated beginning in Windows Media Services 9 Series so that support for MMS streaming is restricted to Windows Media Player for Windows XP or earlier. Support for the MMS streaming protocol was removed beginning with Windows Media Services 2008.