Tiers

To illustrate the difference between single-tier scheduling and hierarchical scheduling policies, consider a simple case where, on service ingress, three queues are created for gold, silver, and bronze service, and are configured as follows:

• gold

  CIR = 10 Mb/s, PIR = 10 Mb/s

• silver

  CIR = 20 Mb/s, PIR = 40 Mb/s

• bronze

  CIR = 0 Mb/s, PIR = 100 Mb/s

In the router, the CIR is used for profiling of traffic (in-profile or out-of-profile), and the PIR is the rate at which traffic is shaped out of the queue. In single-tier scheduling, each queue can burst up to its defined PIR, which means up to 150 Mb/s (10 Mb/s + 40 Mb/s + 100 Mb/s) can enter the service.

In a simple example of a hierarchical scheduling policy, a superior (or parent) scheduler can be created for the gold, silver, and bronze queues that limits the overall rate for all queues to 100 Mb/s. In this hierarchical scheduling policy, the customer can send in any combination of gold, silver, and bronze traffic conforming to the defined PIR values and not to exceed 100 Mb/s.