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Understanding Quality of Service (QoS) in Unified Messaging

Topic Last Modified: 2009-11-20

Microsoft Exchange Server 2010 Unified Messaging (UM) supports DiffServ through Differentiated Services Code Point (DSCP) marking.

In Windows Server 2008, TCP/IP performs DiffServ marking when you've installed the Quality of Service (QoS) Packet Scheduler. When you install the Unified Messaging server role on a computer that's running Windows Server 2008 with the QoS Packet Scheduler installed, all outgoing Unified Messaging packets will be marked with a DSCP value that's configured. However, you can change this value for the packets by using Registry Editor or by modifying the Group Policy. For more information about DSCP marking, see Differentiated Services Code Point (DSCP) overview. By default, the QoS Packet Scheduler is installed on Windows Server 2008.

The Microsoft Exchange Unified Messaging service doesn't perform any classification of network packets. However, the media platform that's included with Unified Messaging instructs the Microsoft Windows networking stack that all audio packets are to be marked as Guaranteed Service. The operating system will then use Group Policy settings to determine how the data packets should be marked and then mark the TOS field of the IP header. For more information about QoS in Windows, see How QoS Works.

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The media stack QoS marking is performed on UDP traffic only because TCP traffic has its own flow control.

You can enter IP addresses and IP address ranges in the Internet Protocol Version 4 (IPv4) format, Internet Protocol Version 6 (IPv6) format, or both formats. However, when you install the Unified Messaging server role on Windows Server 2008, you must have the IPv4 protocol stack enabled with or without having the IPv6 protocol stack enabled. This is because there are limitations with the telephony and speech components that are required and used by Unified Messaging.

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Layer 3 network devices, such as routers, must also support DiffServ.
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