This article was previously published under Q267310
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When you create a .asx file to point to a source file or stream on a Windows Media server, you can specify the way the protocol rollover works.
Usually, when you create a .asx file to point to a stream on a Windows Media server, you use the MMS protocol (for example, mms://myserver/sample.asf or mms://myserver/station1). The Windows Media Player interprets this URL and tries the UDP protocol (MMSU). If the player is unable to connect through UDP (for example, if the player is behind a firewall that doesn't allow UDP), it tries the TCP protocol (MMST), and then it tries HTTP if it can't make a connection with TCP on the desired port. This protocol rollover takes place by moving from the most efficient protocol (UDP) to the least efficient (http) protocol, because not all firewalls have the necessary ports open to play Windows Media streams. See the following article for information on the ports used by Windows Media Services:
189416 Firewalls and Ports Used by Windows Media Services
When you create your .asx file, you can specify the way the protocol rollover takes place. You can place multiple URLs in a single <ENTRY> tag. By doing this, the player first tries the first item in the entry. If, and only if it fails, does the player go to the second URL in the entry tag. The following is an example .asx file:
By using this .asx file, the player does not use UDP as the first protocol that it tries. If you know that no clients are going to be connecting to the server through UDP, this can make a player connection faster because the player doesn't have to attempt UDP and time out.
You can also use .asx files in a similar way if you want to set up rollover to multiple computers. Your first HREF tag can point to your main server and the second HREF points to a backup Windows Media Server. Keep in mind that this does not balance the load, but rather it provides a backup server. For example: