Configuring Hierarchical Modular QoS on Cisco ASR 9000 Series Routers
Information About Hierarchical QoS
QC-129
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
Three-Parameter Scheduler
In hierarchical QoS, if a policy is configured with queueing classes at any level in the hierarchy, then the
traffic for different classes needs to be scheduled according to certain rules of the scheduler based on the
configuration. The Three-Parameter Scheduler is a queueing algorithm that uses the following
parameters to control traffic:
• Minimum bandwidth using the bandwidth command
• Excess bandwidth using the bandwidth remaining command
• Maximum bandwidth using the shape average command
The Three-Parameter Scheduler can be implemented in one-level, two-level, or three-level policies. In
Example 4, a one-level policy is a sample configuration for a three-parameter scheduler.
For the purposes of this example, if policy_3parameter_scheduler is applied to a T1 serial interface and
the T1 interface link bandwidth is 1536 kbps, then the link bandwidth distribution for each class is as
follows:
• Class A is configured explicitly for minimum, maximum, and excess bandwidth. Class A receives a
guaranteed minimum bandwidth of 30 percent of 1536 kbps (460.8 kbps) and 80 percent of
remaining (excess) bandwidth. When other classes are not using all of their bandwidth share, class
A can receive a maximum bandwidth of up to 50 percent of the link bandwidth (768 kbps).
• Class B is configured explicitly for minimum and excess bandwidth. Class B receives a guaranteed
minimum bandwidth of 60 percent of 1536 kbps (921.6 kbps) and10 percent of remaining (excess)
bandwidth. If maximum bandwidth is not explicitly configured, the default maximum bandwidth is
the link bandwidth (1536 kbps— equal to a configuration of shape percent 100). When other
classes are not using all of their bandwidth share, class B can receive a maximum bandwidth of up
to 100 percent of the link bandwidth.
• Class class-default is not configured explicitly with any queueing parameters. There is no default
minimum bandwidth. If maximum bandwidth is not explicitly configured, the default maximum
bandwidth is the link bandwidth (1536 kbps). When other classes are not using all of their bandwidth
share, class-default can receive a maximum bandwidth of up to 100 percent of the link bandwidth.
For excess bandwidth, because class A and class B receive a total of 90 percent of remaining
(excess) bandwidth, class-default receives the remaining 10 percent.
Example 4 Three-Parameter Scheduler in a One-Level Policy
policy-map policy_3parameter_scheduler
class A
bandwidth percent 30 <----------------- minimum bandwidth
bandwidth remaining percent 80 <-----------excess bandwidth
shape average percent 50 <------------maximum bandwidth
class B
bandwidth percent 60
bandwidth remaining percent 10
class class-default
Support for Three-Parameter Scheduler in Hierarchical Policies
In some cases, a scheduler might not support the three parameters at all levels in hierarchical policies.
ASR 9000 Ethernet Line Cards
Queueing is supported at all levels of hierarchical policies:
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