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Differentiated Services Code Point (DSCP) enables packets that pass through network devices that operate on Layer 3 information (such as routers) to have their relative priorities differentiated from one another.
You establish DSCP by setting the first six bits of the Type of Service (TOS) field in the IP header. DSCP determines IP precedence, but maintains backward compatibility. With DSCP marking, Layer 3 devices can establish aggregated precedence-based queues and provide better service to packets that have a higher relative priority. This is helpful when packet services are subject to queuing, such as when there are significant network traffic loads associated with streaming media presentations and other real-time data streams. For DSCP to be effective, Layer 3 devices must be DSCP-enabled.
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
Warning This article contains information about editing the namespace. Before you edit the namespace, verify that you have a backup copy that you can restore if a problem occurs. If you edit the namespace incorrectly, you can cause serious problems that may require you to reinstall any product that uses the namespace. Microsoft cannot guarantee that problems that result if you incorrectly edit the namespace can be solved. Edit the namespace at your own risk. You can set the Type of Service (TOS) bits in the IP header by editing the registry, and by editing the properties section of the WMS Unicast Data Writer plug-in in the ServerNamespace.xml file. To edit the ServerNamespace.xml file that the server uses, follow these steps:
Stop the Windows Media Services (at a command prompt, type net stop wmserver).
Move to the directory where the namespace file is located (%SystemRoot%\system32\windows media\server).
Open the ServerNamespace.xml file in a text editor, such as Notepad.
Locate and then expand the Unicast Data Sink node in the namespace. In the next steps, you will expand a node under each successive node.
Expand the Object Store sub-node.
Expand the WMS Unicast Data Writer sub-node.
Expand the Properties sub-node.
Add the following line under the Properties sub-node:
You can change the value from 0x00 to the appropriate setting for the IP TOS field. TOS is an 8-bit field. The 6 bits that are least significant are used for the TOS setting, and the 2 bits that are most significant are used for early congestion notification (ECN enabled and ECN reported).
Note the following:
Changes in this value affect only UDP-based protocols, and do not affect TCP protocols.
Although the namespace value is set under the Unicast Data Writer, the same change also affects Multicast streaming.
Additionally, you must also modify the registry as follows: