Table Of Contents
Configuring Burst Size in Low Latency Queueing
Supported Standards, MIBs, and RFCs
Configuring the LLQ Burst Size
Burst Size Configuration Example
Configuring Burst Size in Low Latency Queueing
This feature module describes the Configuring Burst Size in Low Latency Queueing feature. This document includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
This feature extends the functionality available with low latency queueing (LLQ). This feature allows customers to specify the Committed Burst (Bc) size in LLQ and, therefore, configure the network to accommodate temporary bursts of traffic.
Benefits
With this new functionality, the network can now accommodate temporary bursts of traffic and handle network traffic more efficiently.
Supported Platforms
The Configuring Burst Size in Low Latency Queueing feature runs on all platforms that support LLQ.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
Configuration Tasks
See the following sections for configuration tasks for the Configuring Burst Size in Low Latency Queueing feature. Each task in the list is identified as optional or required.
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Configuring the LLQ Bandwidth
To configure the LLQ bandwidth, use the following command in policy-map class configuration mode:
Router# priority bandwidth
Specifies the maximum amount of bandwidth (in kpbs) for the priority traffic.
Configuring the LLQ Burst Size
To configure the LLQ burst size, use the following command in policy-map class configuration mode:
Router# priority bandwidth burst
Specifies the burst size in bytes. The range is 32 to 2 million.
Verifying the LLQ Burst Size
To verify the LLQ burst size, use one of the following commands in EXEC mode:
Configuration Examples
This section provides the following configuration example:
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Burst Size Configuration Example
The following example configures the burst parameter to 1250 bytes for the class called Voice. The class called Voice has an assigned bandwidth of 1000 kbps.
policy policy1class Voicepriority 1000 1250Command Reference
This section documents the modified priority command. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
priority
To give priority to a class within a policy map, use the priority policy-map class configuration command. To disable the strict priority queue, use the no form of this command.
priority bandwidth burst
no priority [bandwidth] [burst]
Syntax Description
Defaults
There are no default behaviors or values for the bandwidth argument.
The default burst size is calculated based on a 200-millisecond interval and the bandwidth configured for low latency queueing (LLQ).
Command Modes
Policy-map class configuration
Command History
Usage Guidelines
This command configures LLQ, providing strict priority queueing for class-based weighted fair queueing (CBWFQ). Strict priority queueing allows delay-sensitive data such as voice to be dequeued and sent before packets in other queues are dequeued, giving delay-sensitive data preferential treatment over other traffic.
The priority command allows you to set up classes based on a variety of criteria (not just User Datagram Protocol (UDP) ports) and assign priority to them, and is available for use on serial interfaces and ATM permanent virtual circuits (PVCs). A similar command, ip rtp priority, allows you to stipulate priority flows based only on UDP port numbers and is not available for ATM PVCs.
The bandwidth argument is used to specify the maximum amount of bandwidth allocated for packets belonging to a class configured with the priority command. The bandwidth parameter both guarantees bandwidth to the priority class and restrains the flow of packets from the priority class.
When the device is not congested, the priority class traffic is allowed to exceed its allocated bandwidth. When the device is congested, the priority class traffic above the allocated bandwidth is discarded.
The burst argument is used to specify the burst size and, therefore, configure the network to accommodate temporary bursts of traffic.
Remember the following guidelines when using the priority command:
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Examples
The following example configures strict priority queueing with a guaranteed bandwidth of 50 kbps for the policy map called policy1:
policy-map policy1class voicepriority 50Configuring the priority command in multiple classes provides the ability to police the priority classes individually. For an example, refer to the following configuration:
policy-map policy1class voice1priority 24class voice2priority 48class databandwidth 20In the example, voice1 and voice2 classes of traffic are served in a strict priority manner. The voice1 and voice2 classes are rate-limited to 24 kbps and 48 kbps individually. The class data is guaranteed a bandwidth of 20 kpbs.
In the following example, the Voice class is limited to 1000 kbps of traffic but the Voice class can accommodate temporary traffic bursts of up to 1250 bytes. The Voice class is provided strict priority.
policy policy1class Voicepriority 1000 1250Related Commands