Why Use QoS Policy?

As traffic increases on your network, it is increasingly important for you to balance network performance with the cost of service – but network traffic is not normally easy to prioritize and manage.

On your network, mission-critical and latency-sensitive applications must compete for network bandwidth against lower priority traffic. At the same time, some users and computers with specific network performance requirements might require differentiated service levels.

The challenges of providing cost-effective, predictable network performance levels often first appear over wide area network (WAN) connections or with latency-sensitive applications, like voice over IP (VoIP) and video streaming. However, the end-goal of providing predictable network service levels applies to any network environment (for example, an Enterprises’ local area network), and to more than VoIP applications, such as your company’s custom line-of-business applications.

Before you create a QoS policy, it is important that you understand the two key QoS controls that are used to manage network traffic:

1- Differentiated Services Code Point (DSCP)

You can create QoS policies that define network traffic priority with a Differentiated Services Code Point (DSCP) value that you assign to different types of network traffic.

The DSCP allows you to apply a value (0–63) within the Type of Service (TOS) field in an IPv4 packet’s header, and within the Traffic Class field in IPv6.

The DSCP value provides network traffic classification at the Internet Protocol (IP) level, which routers use to decide traffic queuing behavior.

For example, you can configure routers to place packets with specific DSCP values into one of three queues: “high priority”, “best effort”, or “lower than best effort”.

By default, Windows traffic has a DSCP value of 0.

2- Throttle Rate

You can also limit an application’s outbound network traffic by specifying a throttle rate in QoS Policy.

A QoS policy that defines throttling limits determines the rate of outbound network traffic. For example, to manage WAN costs, an IT department might implement a service level agreement that specifies that a file server can never provide downloads beyond a specific rate.

Configuration Steps

Open Server Manager, click Tools and then click Group Policy Management.

Right-click on the domain name, and then click Create a GPO in this domain and Link it here.

In the New GPO dialog box, in the Name text box, type DSCP VoIP GPO, and then click OK.

Now In the navigation pane, right-click  DSCP VoIP GPO, and then click Edit.

Expand the Windows Setting section of the Local Computer Policy and right click the Policy-based QoS selection

Now In the navigation pane, under Computer Configuration ⇾ Policies ⇾ Windows Settings. Right click Policy-base QoS and select Advance QoS Settings then go to the DSCP Marking override tab. Check the Control DSCP marking checkbox and select Allowed and Click OK.

Again, right-click  Policy-base QoS, and then click Edit.

In the Policy-based QoS configuration pop-up provide the desired Policy name.  Then choose the desired value in the “Specify DSCP Value“.  This is the value with which you would like to mark the packets sent from the server. 

Choose the desired value in the “Specify Outbound Throttle Rate“. Once these values has been defined select  the Next button.

Select “Only applications with the executable name:” and type in name of the application like “CiscoJabber.exe”. Then click next.

Apply the policy to any source and destination IP address. And then click next.

Change “Select the protocol this QoS policy applies to” to TCP and UDP, since you need both marked, and allow from any source and destination port since there is a very wide range needed. Then click “Finish”. Now test.

Similar to GPO’s priorities, QoS policies have precedence rules to resolve conflicts when multiple QoS policies apply to a specific set of traffic. For outbound TCP or UDP traffic, only one QoS policy can be applied at a time, which means that QoS policies do not have a cumulative effect, such as where throttle rates would be summed.

In general, the QoS policy with the most matching conditions wins. When multiple QoS policies apply, the rules fall into three categories: user-level versus computer-level; application versus the network quintuple; and among the network quintuple.

By network quintuple, we mean the source IP address, destination IP address, source port, destination port, and protocol (TCP/UDP).

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