Monday, July 12, 2010

Enabling DSCP Marking for OCS 2007 R2

Email I dug up dating 7/3/2009:

While reviewing the following article for Enabling DSCP Marking:

I found following step confusing:

Verifying Group Policy Settings on Computers

In order to support DSCP marking on the servers and client computers in your organization, the Group Policy settings for conforming packets for the two service types used by QoS Packet Scheduler must be enabled and cannot be set to zero. This includes the following:

  • SERVICETYPE_GUARANTEED. This setting guarantees that IP datagrams will arrive within the guaranteed delivery time and will not be discarded due to queue overflows, provided the flow's traffic stays within its specified traffic parameters. This service is intended for applications that need a firm guarantee that a datagram will arrive no later than a certain time after it was transmitted by its source.
    The Real Time Media Communications stack marks the RTP/SRTP audio packets (default payload type value equal to 0, 3, 4, 8, 13, 97, 101, 111, 112, 114, 115, 116, or 118) as SERVICETYPE_GUARANTEED. This marking is off by default. To enable QoS on high-definition video, also update the following registry key to set the value to 250000 bytes per sec (2 Mbps):
  • The SERVICETYPE_CONTROLLEDLOAD setting provides an end-to-end QoS that closely approximates transmission quality provided by best-effort service, as expected under unloaded conditions from the associated network components along the data path.
    Applications that use SERVICETYPE_CONTROLLEDLOAD may therefore assume the following:
    • The network will deliver a very high percentage of transmitted packets to its intended receivers. In other words, packet loss will closely approximate the basic packet error rate of the transmission medium.
    • Transmission delay for a very high percentage of the delivered packets will not greatly exceed the minimum transit delay experienced by any successfully delivered packet.
    • The Real Time Media Communications stack marks the RTP/SRTP video packets (default payload type value equal to 34 or 121) as SERVICETYPE_CONTROLLEDLOAD. This marking is off by default.

What got me confused was if there was a group policy available to be applied to the OU with the computers or on the computer object itself and if so, is this GPO available for download OR is there documentation on how to create a new one and set the parameters?

I went ahead to post this on the Microsoft Partner Forum support and received the following answer:


Thanks for your post. I’m Paolo and I will assistant you within this thread.

From your description, you need some help and clarification about QoS feature of OCS audio and video traffic.

If I have any misunderstand, please let me know.



I read that article carefully. Actually, I agreed with you that the article you have mentioned is really quite confusing. Especially, client side configuration.

Actually, if we enabled server side QoS through WMI, the media traffic will be marked DSCP automatically.

This setting is provided by inbound for communicator client.

Moreover, we don’t need to modify the group policy because the default setting actually matched the RTC service. (UC is designed to match the default QoS setting)

“SERVICETYPE_GUARANTEED” is 40 by default and RTC audio is exactly 40.

This matched the default settings.

The same as “SERVICETYPE_CONTROLLEDLOAD”. It is used for video traffic.

As a conclusion, I provide a steps to enable QoS for OCS system.



Enable QoS on server side:

1. FE server

We configure FE setting through WMI to enable QoS.

2. Mediation server.

This is similar to FE server

3. Communicator client side:

· Open the Registry Editor.

· Create the following registry key:



· Restart the Office Communicator 2007 R2 service.

· Install QoS Packet Scheduler

· Repeat the preceding steps on each desktop, laptop, and attendant client.

After that, QoS will be enable on for OCS a/v traffic.

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