The first step in defining the QoS policy is organizing traffic flows into classes. You do not need to create classes for every type of traffic on a Diffserv network. Moreover, depending on your network topology, you might have to create a different QoS policy for each IPQoS-enabled system. For an overview of classes, see IPQoS Classes.
Before defining classes, you should determine which systems on your network are to be IPQoS-enabled, as identified in Preparing a Network for IPQOS.
Create a QoS planning table for organizing the QoS policy information, as shown in Figure 1, Table 1, QoS Planning Template.
Perform the remaining steps for every QoS policy that is on your network.
Define the classes to be used in the QoS policy.
For guidelines for analyzing network traffic for possible class definitions, see Using Classes of Service to Prioritize Traffic .
List the classes in the QoS planning table.
Assign a priority level to each class.
For example, use priority level 1 to represent the highest-priority class, and assign descending-level priorities to the remaining classes. This priority level is for organizational purposes only. You can assign the same priority to more than one class if appropriate for your QoS policy.
In addition to assigning a PHB to a class, you can also define a priority selector in a filter for the class. The priority selector is active on the IPQoS-enabled host only. Suppose several classes with equal rates and identical DSCPs sometimes compete for bandwidth as they leave the IPQoS system. The priority selector in each class can further order the level of service that is given to the otherwise identically valued classes.
When you finish defining classes, you next define filters for each class, as explained in How to Define Filters in the QoS Policy.