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Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 22 Hierarchical Scheduling and Queuing
MQC Hierarchical Queuing with 3-Level Scheduler
For more information about the 4 level scheduler, see the
“4-Level Scheduler” section on page 22-10
Feature History for MQC Hierarchical Queuing with 3-Level Scheduler
Prerequisites for MQC Hierarchical Queuing with 3-Level Scheduler
Traffic classes must be configured on the router using the
class-map
command.
Restrictions for MQC Hierarchical Queuing with 3-Level Scheduler
•
We recommend that the sum of all priority traffic on a given interface not exceed 90 percent of the
physical bandwidth of that interface.
•
The 3-level scheduler does not support bandwidth propagation. Therefore, you cannot configure a
bandwidth guarantee for any queue other than a priority queue.
•
To allow oversubscription provisioning, the admission control check is not performed.
•
The sum of all priority traffic running on a given port must be less than or equal to 90 percent of the
port bandwidth.
Scheduling Hierarchy
As shown in
Figure 22-1
, the 3-level scheduler uses the following scheduling hierarchy to allocate
bandwidth for subscriber traffic:
•
Class layer—The 3-level scheduler uses virtual-time calendars to schedule class queues.
•
Logical layer (subinterface, session, or ATM VC)—Virtual-time calendars perform weighted round
robin based on the weight of the logical interface and the number of bytes dequeued.
•
Physical layer (interface or ATM virtual path)—A real-time calendar ensures that the maximum rate
for the class and the logical interface are not exceeded.
By using VP and VC scheduling with existing Cisco 10000 ATM line cards, the scheduler supports
priority propagation: cell-based VP shaping in the segmentation and reassembly (SAR) mechanism with
frame-based VC scheduling in the performance routing engine 3 (PRE3).
Cisco IOS Release
Description
PRE Required
Release 12.2(31)SB2
This feature was introduced and implemented on the
Cisco 10000 series router for the PRE3.
PRE3
Release 12.2(33)SB
This feature was introduced on the PRE4 for the
Cisco 10000 series router.
PRE4
