You experience performance issues in Office Communications Server 2007 R2 during NTLM authentication

You experience performance issues in Microsoft Office Communications Server 2007 R2 during NTLM authentication. These performance issues may trigger one or more of the following symptoms:

• You experiencehigh CPU usage on an Office Communications Server 2007 R2 front-end server.
• Users who are logged on are logged off.
• Most end-user scenarios such as instant messaging, presence, conferencing, and audio/video calls are unreliable.

These issues occur when both of the following conditions are true:

• Many endpoints perform NTLM authentication.
• A long delay occurs on the network links either between the Office Communications Server 2007 R2 front-end server and its domain controller or between the domain controller for the Office Communications Server 2007 R2 front-end server and the domain controller for the user authentication domain.

To fix this problem, apply the following update:

To work around these issues, make sure that the delay is acceptable on the network links between the Office Communications Server 2007 R2 front-end server and its domain controller.Also make sure that the delay is not too long on the network links between that domain controller and the domain controllers for the user authentication domain.

Note The network link delay in seconds should be less than the number of Netlogon secure channels (default is 2) divided by the expected number of user logons per second. For example, for a delay of 0.1 seconds, the logon rate should not exceed 20 per second.

If you cannot decrease the network link delay, try to increase the registry entry for Netlogon on the server and on the server's domain controller.

For more information about the MaxConcurrentApi registry entry, click the following article numbers to view the articles in the Microsoft Knowledge Base: