Windows 7 / Networking

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Policy-Based QoS

The cost of bandwidth has fallen significantly in the last several years, but network congestion is still a problem. As more people and organizations begin to use real-time networking services, such as Voice over IP (VoIP), multimedia streaming, and video conferencing, it is obvious that increasing bandwidth alone cannot solve network quality problems.

Note Windows Vista and Windows 7 support Quality Windows Audio Video Experience (qWAVE), which provides QoS support for streaming audio and video across home networks. Because this resource kit focuses on enterprise networking, qWave is not discussed in detail. Instead, all references to QoS refer to enterprise QoS, also known as eQoS.

Policy-based QoS in Windows Vista and Windows 7 enables domain-wide management of how computers on your network use bandwidth. This technology can solve network problems and make possible the following scenarios:

• Enable real-time traffic by prioritizing more important applications, such as VoIP, over lower-priority traffic, such as browsing the Web or downloading e-mail.
• Customize bandwidth requirements for groups of users and computers. For example, you can prioritize traffic for your IT Support Center over other users to increase responsiveness when managing and troubleshooting computers.
• Minimize the negative impact of high-bandwidth, low-priority traffic, such as backup data transfers, by using prioritization and throttling.

Network congestion problems occur because high-bandwidth applications tend to consume all available bandwidth, and applications are not written to give central bandwidth control to IT administrators. Adding more bandwidth does not usually solve these problems. Instead, adding more bandwidth only leads to applications consuming the newly available capacity. IT administrators need a central means to control and allocate bandwidth resources based on the needs of their business.

Policy-based QoS enables you to make the most of your current bandwidth by enabling flexible bandwidth management through Group Policy settings. With Policy-based QoS, you can prioritize and/or throttle outbound network traffic without requiring applications to be modified for QoS support. You can use Differentiated Services Code Point (DSCP) marking to configure QoS policies to outbound traffic so that network equipment can prioritize it or specify a maximum throttle rate. DSCP marking is useful only if prioritization is enabled in routers. Almost all enterprise-class routers support DSCP prioritization; however, it is usually disabled by default.

Each computer running Windows Vista and Windows 7 can prioritize or throttle outbound traffic based on a mix of any of the following conditions:

• Group of users or computers based on an AD DS container, such as a domain, a site, or an organizational unit
• Sending application
• Source or destination IPv4 or IPv6 address (including network prefix length notation, such as 192.168.1.0/24)
• Source or destination Transmission Control Protocol (TCP) or UDP port number
• For computers running Windows 7 only, the Uniform Resource Locator (URL) of a Web site being accessed with HTTP or Hypertext Transfer Protocol Secure (HTTPS)

Additionally, Windows 7 (when acting as a Web server) can now prioritize Web traffic based on the URL, allowing you to assign a lower priority to nonessential Web sites and a higher priority to critical Web sites. Because this is primarily a server feature, it is not discussed in detail here.

Note Windows Vista and Windows 7 include a new implementation of the QoS component in the Pacer.sys NDIS 6.0 lightweight filter driver, located in %SystemRoot% \System32\Drivers. Pacer.sys replaces Psched.sys, which is used in the Windows Server 2003 and Windows XP operating systems. It continues to support the Generic QoS (GQoS) and Traffic Control (TC) application programming interfaces (AP Is) provided by Microsoft Windows 2000, Windows XP, and Windows Server 2003. Therefore, existing applications that use QoS will work with Windows Vista and Windows 7. For more information about these AP Is, see "The MS QoS Components" at http://technet.microsoft.com/en-us/library/bb742475.aspx.