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Overview of Policy-Based QoS

Applies To: Windows Server 2008 R2

Quality of Service (QoS) for networks is an industry-wide set of standards and mechanisms for ensuring high-quality performance for critical applications. Network administrators can use QoS mechanisms to prioritize, and manage the sending rate for, outgoing network traffic. The use of these mechanisms ensures that resources are used efficiently to provide the required level of service.

In Windows Server® 2008 R2 and Windows 7®, policy-based QoS combines the functionality of QoS standards with the manageability of Group Policy. This combination allows for easy application of QoS policies to user login sessions and computers.

About QoS policies

A QoS policy wizard in the Group Policy Management Console (GPMC) helps you configure QoS policies in a Group Policy object (GPO). By linking the GPO to Active Directory containers such as sites, domains, and organizational units (OUs), you can apply the QoS policy to manage outbound traffic for user login sessions or computers that you define. For example, you can create QoS policies to mark as high priority all traffic from a group of servers that run a critical enterprise resource planning application.

Policy-based QoS settings in Windows Server 2008 R2 and Windows 7 enable you to prioritize or manage the sending rate for outbound network traffic based on the following:

  • Sending application.

  • URL. (This support is new in Windows Server 2008 R2 and Windows 7.)

  • Source or destination Internet Protocol version 4 (IPv4) or Internet Protocol version 6 (IPv6) addresses or address prefixes.

  • Source or destination Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) ports or port ranges.

  • Protocol (TCP or UDP).

You use a differentiated services code point (DSCP) value to specify the priority of traffic. DSCP values are defined in RFC 2474. You use throttle rate to specify the sending rate of traffic. You can use DSCP marking and throttling together. For example, you can create a QoS policy to mark all traffic responding to requests from http://www.contoso.com with a DSCP value of 44 and limit that traffic to an aggregate outbound rate of 500 kilobytes per second (KBps).

In the IPv4 header, the DSCP value is stored in the Type of Service (TOS) field. In the IPv6 header, this value is stored in the Traffic Class field. DSCP-capable routers read the DSCP value and place a packet to be forwarded into a queue. By configuring queues and DSCP values for routers on your network, you can achieve differentiated levels of service for DSCP-marked traffic on your network. For more information, see RFC 2474 (http://go.microsoft.com/fwlink/?LinkId=139654).

In addition to the standard QoS policy settings that enable you to specify a DSCP value and a throttle rate, you can use advanced QoS settings to manage the throughput level of inbound TCP traffic and to specify whether DSCP marking requests from applications (as opposed to marking requests from QoS policies) are allowed or ignored.

Additional references

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