This article describes how to use network throttling to control network performance on a computer that is running Windows Vista.

Back to the top

Multimedia traffic

The processing of network packets on a computer is a resource-intensive task. On high bandwidth links, network traffic consumes even more system resources. Additionally, multimedia programs are time sensitive, and such programs require prioritized access to CPU resources.

For more information about processing that is prioritized for multimedia programs, visit the following Microsoft Developers Network Web site:

Back to the top

Windows throttling mechanism

Because multimedia programs require more resources, the Windows networking stack implements a throttling mechanism to restrict the processing of non-multimedia network traffic to 10 packets per millisecond.

The throttling will come into effect only when you are running multimedia programs that are time sensitive. However, this throttling mechanism can potentially cause a decrease in network performance during the active multimedia playback period. This decrease in performance is likely to occur only on high speed networks that are saturated to maximum capacity.

Back to the top

How to improve network performance in Windows Vista

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

In circumstances where you experience a decrease in network performance, you can control the throttling rate to improve network performance in Windows Vista. However, you must do this with caution because this may affect the quality of multimedia playback.

To configure the throttling rate, change the value of the NetworkThrottlingIndex registry entry under the following registry subkey:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Multimedia\SystemProfile\
Name : NetworkThrottlingIndex
Value type : DWORD
Value data : From integer 1 through integer 70 (Decimal) (Decimal)

By default, the value for the NetworkThrottlingIndex registry entry is set to 10. When the NetworkThrottlingIndex registry entry does not exist, the behavior resembles the default behavior. Network throttling can be completely turned off by setting the value to FFFFFFFF (hexadecimal). You must restart the computer after you make a change to the value of the NetworkThrottlingIndex registry entry.

Important The default value is unlikely to cause degradation in network performance in most common Internet usage scenarios that use broadband connections. We recommend that you only use the throttling mechanism after you fully understand the tradeoff between multimedia playback quality and network performance.

Back to the top