Source Class Usage Overview

Source class usage (SCU) is a logical extension of the destination class usage (DCU) concept. DCU was created so that Juniper Networks customers could count on a per-interface basis how much traffic was sent to specified prefixes. Figure 1 shows a service provider edge (PE) router diagram.

However, DCU limits your ability to keep track of traffic moving in the reverse direction. It can account for all traffic that arrives on a core interface and heads toward a specific customer, but it cannot count traffic that arrives on a core interface from a specific prefix. For example, DCU can process cumulative traffic headed toward interface fe-0/0/0, but cannot differentiate between traffic coming only from 10.3.0.0/16 and traffic coming from all prefixes.

You can track source-based traffic by using SCU, which allows you to monitor the amount of traffic originating from a specific prefix. With this feature, usage can be tracked and customers can be billed for the traffic they receive.