Introduction Prerequisites
Requirements
Components Used
Conventions Configure
Network Diagram
Configurations Verify Troubleshoot Related Information
Introduction
This sample configuration illustrates the Low Latency Queueing feature. The Low Latency Queueing feature
brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ). Configured by the
priority command, strict priority queueing gives delay-sensitive data, such as voice, preferential treatment
over other traffic. With this feature, delay-sensitive data is sent first (before packets in other queues are
treated). Low Latency Queueing documentation provides additional details about this feature.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
Low Latency Queueing has been supported on all platforms running Cisco IOS® Software release12.0(7)T
and later. For further information on this, refer to Supported Platforms.
For Cisco 7500 routers, Low Latency Queueing is supported in Cisco IOS Software release 12.0.(7)XE and
later. For more information, refer to Supported Platforms.
For an overview of feature evolution on Cisco IOS Software releases, refer to Feature Overview.
The information in this document was created from the devices in a specific lab environment. All of the
devices used in this document started with a cleared (default) configuration. If your network is live, make sure
that you understand the potential impact of any command.
Conventions
For more information on document conventions, refer to Cisco Technical Tips Conventions.
Configure
In this section, you are presented with the information to configure the features described in this document.
Note: To find additional information on the commands used in this document, use the Command Lookup
Tool ( registered customers only) .
Network Diagram
This document uses this network setup:
Note: In this configuration:
The Cisco 7200s 2 and 4 are equipped with a PA-A3 and configured with the CBWFQ Low Latency
Queueing feature.
A policy-map statement is configured to classify the packets originating from Router 1, 10.2.2.2, and
directed to 10.6.6.2 (device connected to Router 4). Low Latency Queueing is configured to give
priority to this flow and allocate 70K of the 100K SCR vbr-nrt PVC configured between the two
routers.
A ping traffic simulates the constant traffic flow between Source 10.2.2.2 and Destination 10.6.6.2. A
ping traffic with timeout 0 generated from Router 3 towards 10.5.5.10 connected to Router 4 will
simulate the congesting flow.
The queue-limit keyword under class-default is used to limit the queue depth of the congesting
traffic.
The tx-ring-limit command is used to reduce the PA First In, First Out (FIFO) queue.
The show queue atm2/0.1 command shows the null weight assigned to the high priority flow. Any
packet matching that flow is immediately scheduled for transmission. Packets assigned to the default
class are queued up to the maximum queue-limit threshold and dropped if the congestion state
persists.
Configurations
This document uses these configurations:
Cisco 7200 Router 2
Cisco 7200 Router 4
Verify
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool ( registered customers only) , which allows
you to view an analysis of show command output.
show queueLists fair queueing configuration and statistics for a particular interface.
show policy-map interfaceDisplays the configuration of all classes configured for all service
policies on the specified interface.
