CHAPTER
22-1
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
22
Hierarchical Scheduling and Queuing
The performance routing engine (PRE3 and PRE4) supports a hierarchical queuing framework (HQF)
for scheduling and queuing. This HQF architecture enables service providers to manage their QoS
services at three or four layers of hierarchy. The scheduler uses the HQF to allocate excess bandwidth
among the subscriber queues and logical interfaces. The scheduler services queues based on the
maximum rate and bandwidth-remaining ratio you specify.
This chapter describes hierarchical scheduling and queuing, and includes the following topics:
• Hierarchical Queuing Framework, page 22-1
• MQC Hierarchical Queuing with 3-Level Scheduler, page 22-5
• 4-Level Scheduler, page 22-10
• Related Documentation, page 22-12
Hierarchical Queuing Framework
The hierarchical queuing framework (HQF) defines a QoS architecture for implementing hierarchical
packet scheduling and queuing on the PRE3 and PRE4. The HQF enables service providers to manage
their QoS at three or four levels of hierarchy. The 3-level HQF scheduler uses the following hierarchy:
• Physical layer—Used for shaping the physical interface such as the OC-3 port.
• Logical layer—Used to schedule subinterfaces such as a VLAN or PPP sessions.
• Class layer—Used for class queues, defined using the modular QoS command line interface (MQC)
policy map.
The 4-level HQF scheduler uses the same hierarchy as above, except that it splits the logical layer into
an upper logical layer for sessions and a lower logical layer for subinterfaces. For more information, see
the
“4-Level Scheduler” section on page 22-10.
The parallel express forwarding (PXF) engine performs all packet-level scheduling using the HQF.
Figure 22-1 shows the 3-level HQF hierarchy.
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