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This feature module describes the Configuring Burst Size in Low Latency Queueing feature. This document includes the following sections:
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.
With this new functionality, the network can now accommodate temporary bursts of traffic and handle network traffic more efficiently.
The Configuring Burst Size in Low Latency Queueing feature runs on all platforms that support LLQ.
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.
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.
To configure the LLQ bandwidth, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
Router#priority bandwidth | Specifies the maximum amount of bandwidth (inkpbs) for the priority traffic. |
To configure the LLQ burst size, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
Router#priority bandwidth burst | Specifies the burst size in bytes. The range is 32 to 2million. |
To verify the LLQ burst size, use one of the following commands in global configuration mode:
This section provides the following configuration example:
policy policy1 class Voice priority 1000 1250
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.
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
Syntax Description
bandwidth Guaranteed allowed bandwidth (in kbps) for the priority traffic. Beyond the guaranteed bandwidth, the priority traffic will be dropped in the event of congestion to ensure that the nonpriority traffic is not starved. burst Burst size in bytes. The range is 32 to 2 million.
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
12.0(6)T This command was introduced. 12.1(3)T The burst argument was added.
Release
Modification
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:
Examples
The following example configures strict priority queueing with a guaranteed bandwidth of 50 kbps for the policy map called policy1:
policy-map policy1 class voice priority 50
Configuring 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 policy1 class voice1 priority 24 class voice2 priority 48 class data bandwidth 20
In the example, voice1 and voice2 classes of traffic are served in a strict priority manner. The voice1 and voice2 classes are rate-limited to 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 policy1 class Voice priority 1000 1250
Related Commands
ip rtp priority Reserves a strict priority queue for a set of RTP packet flows belonging to a range of UDP destination ports. ip rtp reserve Reserves a special queue for a set of RTP packet flows belonging to a range of UDP destination ports. max-reserved-bandwidth Changes the percent of interface bandwidth allocated for CBWFQ, LLQ, and IP RTP Priority. show policy-map interface Displays the configuration of classes configured for service policies on the specified interface or PVC. show queue Displays the contents of packets inside a queue for a particular interface or VC.
Command
Description
Posted: Tue Sep 19 17:49:55 PDT 2000
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