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How to Configure Quality of Service (QoS) for Unified Messaging

 

Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1

Topic Last Modified: 2008-08-27

Microsoft Exchange Server 2007 Service Pack 1 (SP1) Unified Messaging supports DiffServ through Differentiated Services Code Point (DSCP) marking.

In Microsoft Windows Server 2003, TCP/IP performs DiffServ marking when you have installed the Quality of Service (QoS) Packet Scheduler. When you install the Unified Messaging server role on a computer that is running Windows Server 2003 with the QoS Packet Scheduler installed, all outgoing Unified Messaging packets will be marked with a DSCP value that is 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.

The Microsoft Exchange Unified Messaging service does not perform any classification of network packets. However, the media platform that is included with Unified Messaging instructs the 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.

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

By default, the QoS Packet Scheduler component is not enabled on Windows Server 2003 and must be installed. The QoS Packet Scheduler can be installed by adding it as a network service on the properties of a network connection in Windows Server 2003. However, the QoS Packet Scheduler is installed by default on Windows Server 2008.

If Exchange 2007 SP1 is deployed on a computer that is running the Windows Server 2008 operating system, 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, although you can install the Unified Messaging server role on Windows Server 2008, you must have the IPv4 protocol stack enabled with or without the IPv6 protocol stack enabled. This is because there are limitations with the telephony and speech components that are required and are used by Unified Messaging. For more information about Exchange 2007 SP1 support for IPv6 addresses, see IPv6 Support in Exchange 2007 SP1 and SP2.

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

To configure QoS on Exchange 2007 Unified Messaging, you must follow these steps:

Step 1 - Install the QoS Packet Scheduler if the Unified Messaging server is running on Windows Server 2003. If the Unified Messaging server is running on Windows Server 2008, skip this step.

Step 2 - Create the QoSEnabled DWORD value in the registry.

Step 3 - Change the DSCP values from the default setting using Group Policy if needed.

Step 4 - Verify that the DSCP values are set correctly.

CautionCaution:
If the Unified Messaging server role is installed on a computer that is running Windows Server 2008, there are additional steps that must be performed to correctly configure QoS. This is because there are limitations with the media stack that is used with Unified Messaging that prevent QoS from working correctly on Windows Server 2008. You must create a QoS policy that will be applied to all UDP packets that are set by the Microsoft Speech Worker process (SESWorker.exe). For more information about how to configure Policy-based QoS, see Policy-based Quality of Service (QoS).

To perform this procedure, the account you use must be delegated membership in the local Administrators group for the target server.

For more information about permissions, delegating roles, and the rights that are required to administer Exchange 2007, see Permission Considerations.

Also, before you perform these procedures, confirm the following:

To install the QoS Packet Scheduler on a Unified Messaging Server that is running Windows Server 2003
  1. Log on to the Unified Messaging server.

  2. Open Control Panel, and then click Network Connections.

  3. Locate the network connection to enable the QoS Packet Scheduler, right-click this network connection, and then click Properties.

  4. In the network connection properties window, click Install.

  5. In the Select Network Component Type window, click Service, and then click Add.

  6. In the Select Network Service window, click QoS Packet Scheduler.

  7. In the network connection properties window, click Close.

To create the QoSEnabled DWORD value in the registry
  1. Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

  2. Open Registry Editor.

    noteNote:
    The required registry keys are not created when you install the Unified Messaging server role, but they are created when you install Microsoft Office Communications Server 2007.
  3. Locate the following key: HKEY_LOCAL_MACHINE\Software\Microsoft

  4. Right-click Microsoft and create a new registry key named RTC.

  5. Right-click RTC and create a new registry key named Transport.

  6. In the result pane for the Transport key, right-click and click New, and then select DWORD and type QoSEnabled.

  7. Double-click the QoSEnabled DWORD value.

  8. In the Edit DWORD value properties window, in the Value data dialog box, type 1, and then click OK.

  9. Restart the Unified Messaging server to load the QoS settings that are stored in the registry.

When you perform the previous steps, the following default Windows QoS settings will be set on the Unified Messaging server:

  • SERVICETYPE_GUARANTEED (DSCP 40, 0x28)
  • SERVICETYPE_CONTROLLEDLOAD (DSCP 24,  0x18)
To use Group Policy to change the DSCP values
  1. If you want to use different values in the first six bits of the TOS field of the IP packet headers, you can configure your own DSCP values. To do this:

    1. Click Start, click Run type gpedit.msc in the Open dialog box, and then click OK.
    2. In the Group Policy Object Editor window, locate Computer Configuration/Administrative Templates/Network/QoS Packet Scheduler/DSCP value of conforming packets.
    3. In the result pane, double-click Controlled load service type.
    4. In the Controlled load service type Properties window, click Enable.
    5. In the DSCP value dialog box, select the value that you want to use, and then click OK.
    6. In the result pane, double-click Guaranteed service type.
    7. In the Guaranteed service type Properties window, click Enable.
    8. In the DSCP value dialog box, select the value that you want to use, and then click OK.
    9. Close the Group Policy Object Editor window.
    10. Click Start, Run, type Gpupdate.exe /target:UMserver /force in the Open dialog box, and then click OK.
To verify that the correct DSCP values were set
  1. Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

  2. Open Registry Editor.

  3. Locate the following key: HKLM\Software\Policies\Microsoft\Windows\Psched\DiffservByteMappingConforming

  4. These values will be different if you have changed the default DSCP values by using Group Policy. If you have not changed the default DSCP settings by using Group Policy, the following default values will be set:

    • SERVICETYPE_GUARANTEED (DSCP 40, 0x28)
    • SERVICETYPE_CONTROLLEDLOAD (DSCP 24,  0x18)

Office Communications Server 2007 also supports QoS by using Diffserv. To enable QoS marking in your Communications Server 2007 environment, you must do the following:

  1. Enable the QoS Packet Scheduler service on servers and clients. By default, the QoS Packet Scheduler service is enabled on Windows Vista and Windows XP computers. However, by default, it is not enabled on Windows Server 2003 computers. QoS marking is not enabled by default in Office Communications Server because Office Communications Server only runs on Windows Server 2003 and QoS marking depends on the QOS Packet Scheduler service running on both server and client computers. You can use the procedure in Step 1 to install the QoS Packet Scheduler.
  2. Configure the registry key to enable QoS marking of IP packets sent to and from the Office Communications Server server by setting the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\RTC\Transport\QoSEnabled key to 1. Then restart the Communications Server 2007 server to load the QoS settings that are stored in the registry.
  • Use Group Policy to set DSCP values that mark the IP packets if you need values other than the defaults for Guaranteed service type packets (used for audio) and Controlled load service type packets (used for video). You can use the procedure in Step 3 to change the default values. By default, the following settings are applied when you set the QoSEnabled DWORD value:
    • SERVICETYPE_GUARANTEED (DSCP 40, 0x28)
    • SERVICETYPE_CONTROLLEDLOAD (DSCP 24,  0x18)

For more information about QoS and Communications Server 2007, see Voice QoS.

To ensure that you are reading the most up-to-date information and to find additional Exchange Server 2007 documentation, visit the Exchange Server TechCenter.
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