Hierarchical Policer Overview
The Enhanced IQ (IQE) PIC can police traffic at Layer 2 in a hierarchical manner. Hierarchical policing maintains two rates: an aggregate rate and a high-priority, premium rate. The traffic is marked differently depending on service class (currently, the classes are expedited forwarding and nonexpedited forwarding). The expedited traffic has an additional rate configured, the committed information rate (CIR), which is only marked above that limit. If there is no expedited traffic present, then the nonexpedited traffic is able to use the aggregate bandwidth rate before being marked with a packet loss priority. When expedited traffic is present, it is marked when it exceeds the guaranteed rate, but also uses bandwidth from the nonexpedited range.
For example, consider an aggregate rate of 10 Mbps and a premium rate of 2 Mbps for a Fast Ethernet interface. The guaranteed rate is also set at 2 Mbps for expedited forwarding traffic. If there is no expedited traffic present, then nonexpedited traffic can use up to 10 Mbps before being marked. When expedited forwarding traffic is present, the expedited traffic is guaranteed 2 Mbps (of the 10 Mbps) without being marked, but is marked above the 2-Mbps limit. In this case, the nonexpedited forwarding traffic can use the remaining 8 Mbps before being marked.
