Default Forwarding Classes

Table 1 shows the default forwarding class and packet loss priority (PLP) for the well-known DSCPs. It is important to note that although several DSCPs map to the expedited-forwarding and assured-forwarding classes, by default no resources are assigned to these forwarding classes. All of these settings can be changed through configuration.

Table 2 shows the router forwarding classes associated with each well-known DSCP code point and the resources assigned to their output queues.

Table 3 shows the resources assigned to the four forwarding classes in this example.

The table shows how the 95 percent of output link transmission rate and buffer size (queue) resources assigned by default to Q0 (best-effort) are distributed to Q1 (expedited forwarding) and Q2 (assured forwarding). The audiovisual traffic consumes more bandwidth than other applications, but the financial information, although critical, is carried in fewer packets. In keeping with DiffServ specifications, a RED drop profile is applied to the assured forwarding class. The financial data has a strict set of traffic parameters that must be respected.

The three DiffServ assured forwarding classes supported (af11, af12, and af13, with low, medium, and high packet drop probability, respectively) are distinguished by using a low PLP and RED drop profile for af11 and a high PLP and RED for af12 and af13. All of these parameters should be closely monitored initially for performance and adjusted as necessary.