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QoS: ATM CLP-Based Queue Limit

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QoS: ATM CLP-Based Queue Limit

Table Of Contents

QoS: ATM CLP-Based Queue Limit

Contents

Prerequisites for QoS: ATM CLP-Based Queue Limit

Restrictions for QoS: ATM CLP-Based Queue Limit

Information About the QoS: ATM CLP-Based Queue Limit

Feature Overview

Setting Thresholds

Tail Drop

Benefits

How to Configure the QoS: ATM CLP-Based Queue Limit

Setting the Queue Limit

Attaching the Policy Map to an Interface

Verifying the Configuration

Configuration Examples for QoS: ATM-Based CLP Queue Limit

Setting the Queue Limit: Examples

Verifying the Configuration: Examples

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

queue-limit atm clp

Glossary


QoS: ATM CLP-Based Queue Limit


The QoS: ATM CLP-Based Queue Limit feature specifies the maximum size (threshold) of a queue in cells, milliseconds, or microseconds for cell loss priority (CLP) traffic.

Feature History for QoS: ATM CLP-Based Queue Limit

Release
Modification

12.0(30)S

This feature was introduced.


Finding Support Information for Platforms and Cisco IOS Software Images

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Contents

Prerequisites for QoS: ATM CLP-Based Queue Limit

Restrictions for QoS: ATM CLP-Based Queue Limit

Information About the QoS: ATM CLP-Based Queue Limit

How to Configure the QoS: ATM CLP-Based Queue Limit

Configuration Examples for QoS: ATM-Based CLP Queue Limit

Additional References

Command Reference

Glossary

Prerequisites for QoS: ATM CLP-Based Queue Limit

Before using this feature, configure a traffic class and ensure that a policy map exists. To create the traffic class (specifying the appropriate match criteria) and the policy map, use the modular quality of service (QoS) command-line interface (MQC).


Note For a Layer 2 Virtual Private Network (L2VPN) ATM configuration, you do not need to configure a traffic class; the class class-default is used.


Restrictions for QoS: ATM CLP-Based Queue Limit

Weighted random early detection (WRED) based on ATM CLP cannot be used to define the threshold because WRED based on ATM CLP is not supported on Cisco 12000 Series Routers.

You must configure the CLP queue limit (the minimum threshold) and the global queue limit (the maximum threshold) for a particular traffic class in the same units (cells, milliseconds, or microseconds). That is, the unit of measure in the same class and in the same policy map cannot be different. For example, if you specify the CLP queue limit for a particular class in milliseconds, the global queue limit for that class must also be in milliseconds.

You must attach the policy map in the output direction only of the interface.

Information About the QoS: ATM CLP-Based Queue Limit

To configure the QoS: ATM CLP-Based Queue Limit feature, you should understand the following concepts:

Feature Overview

Benefits

Feature Overview

After you specify the CLP queue-limit and the global queue-limit thresholds, you can configure them in policy maps. You can then attach the policy maps to multiple interfaces.

The following sections provide more information about queue limits:

Setting Thresholds

Tail Drop

Setting Thresholds

The queue-limit command allows you to specify or modify the maximum number of packets that the queue can hold (that is, the threshold) for a class configured in a policy map. Packets belonging to a class are subject to the guaranteed bandwidth allocation and the queue limits that characterize the traffic class.

You can specify the queue-limit threshold as cells, milliseconds (ms), or microseconds (us) of queue space. When you specify the queue-limit threshold as cells, milliseconds, or microseconds, it is internally converted to cells by using the visible bandwidth that is available to the class or the ATM virtual circuit (VC).

The queue fills up if the VC receives traffic at a high rate. The CLP queue-limit threshold helps determine which ATM cells get dropped if the queue becomes filled. You can differentiate between traffic by setting the CLP queue-limit threshold to one value and the global queue-limit threshold to another value. For example, if you set your CLP queue-limit threshold for your discard eligible traffic to CLP=1, which is best-effort delivery, and your global queue-limit threshold to CLP=0, which is ensured or guaranteed delivery, the CLP=1 traffic is dropped before the CLP=0 traffic.

Tail Drop

After a queue has reached its configured queue limit, queuing of additional packets to the traffic class causes tail drop to take effect, depending on how the policy map is configured.

Tail drop is a means of avoiding congestion in all traffic and does not differentiate between classes of service. Queues fill during periods of congestion. When the output queue is full and tail drop is in effect, packets are dropped until the congestion is eliminated and the queue is no longer full. Tail drop is used for distributed class-based weighted fair queueing (DCBWFQ) traffic classes.

Figure 1 shows a sample L2VPN configuration for QoS: ATM CLP-Based Queue Limit.

Figure 1 Sample L2VPN Configuration

Benefits

Increased Flexibility

You can specify the CLP queue-limit and the global queue-limit thresholds in cells, milliseconds, or microseconds. These units of measure provide flexibility and allow fine-tuning of the configuration.

More Traffic Control

You can set a CLP queue-limit and a global queue-limit threshold so that you can prioritize traffic when the queue gets full. For example, you can set your discard eligible traffic to CLP=1 so that it is dropped before the CLP=0 traffic.

How to Configure the QoS: ATM CLP-Based Queue Limit

This section provides the following configuration procedure:

Setting the Queue Limit

Attaching the Policy Map to an Interface

Verifying the Configuration

Setting the Queue Limit

The queue-limit atm clp command allows you to specify the maximum size of a queue for a particular traffic class.

To set the queue limit, perform the following steps:

SUMMARY STEPS

1. enable

2. configure terminal

3. policy-map policy-name

4. class {class-name | class-default}

5. bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}


Note For an L2VPN ATM configuration, omit Steps 4 and 5 because there is no classification; all traffic uses the class class-default. Also, you do not have to configure the bandwidth.


6. queue-limit queue-size {cells | ms | packets | us}

7. queue-limit atm clp queue-size {cells | ms | us}

8. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

policy-map policy-map

Example:
Router(config)# policy-map POLICY-ATM

Specifies the name of the policy map to be created. Enters policy-map configuration mode.

Enter the policy map name.

Step 4 

class {class-name | class-default}

Example:

Router(config-pmap)# class CLASS-ATM

Specifies the class so that you can configure or modify its policy. Enters policy-map class configuration mode.

Enter the class name or use the class-default keyword.

Note For an L2VPN ATM configuration, omit this step because there is no classification; all traffic uses the class class-default.

Step 5 

bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}

Example:

Router(config-pmap-c)# bandwidth percent 20

(Optional) Specifies or modifies the bandwidth allocated for a class belonging to a policy map.

Enter the bandwidth to be set or modified.

Note For an L2VPN ATM configuration, omit this step because you do not have to configure the bandwidth.

Step 6 

queue-limit queue-size {cells | ms | packets | us}

Example:

Router(config-pmap-c)# queue-limit 1000 cells

Specifies or modifies the maximum number of packets the queue can hold (that is, the queue limit) for a class configured in a policy map.

Enter the global queue-limit threshold. The unit of measure can be cells, milliseconds, or microseconds.

Step 7 

queue-limit atm clp queue-size {cells | ms | us}

Example:

Router(config-pmap-c)# queue-limit atm clp 100 cells

Specifies the maximum size of a queue for a particular traffic class configured in a policy map.

Enter the CLP queue-limit threshold. The unit of measure can be cells, milliseconds, or microseconds.

Step 8 

exit

Example:

Router(config-pmap-c)# exit

(Optional) Exits policy-map class configuration mode.

Attaching the Policy Map to an Interface

To attach the policy map to an interface, perform the following steps.


Note You can attach policy maps in the output direction only of the interface.


SUMMARY STEPS

1. enable

2. configure terminal

3. interface interface-number

4. pvc [name] vpi/vci [ilmi | qsaal | smds]

5. service-policy {input | output} policy-map-name

6. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface interface-number

Example:
Router(config)# interface atm1/0

Configures an interface or subinterface type and enters interface configuration mode.

Enter the interface type number.

Step 4 

pvc [name] vpi/vci [ilmi | qsaal | smds]

Example:

Router(config-if)# pvc 0/50

Creates or assigns a name to an ATM PVC and specifies the encapsulation type on an ATM PVC. Enters ATM VC configuration mode.

Step 5 

service-policy {input | output} policy-map-name

Example:

Router(config-if-atm-vc)# service-policy output POLICY-ATM

Specifies the name of the policy map to be attached in the output direction only of an interface.

Note Policy maps can be attached only in the output direction of an interface. The direction and the router to which the policy map should be attached vary according to the network configuration. When using the service-policy command to attach the policy map to an interface, be sure to choose the router and the interface direction that are appropriate for the network configuration.

Enter the policy-map name.

Step 6 

exit

Example:

Router(config-if-atm-vc)# exit

(Optional) Exits ATM VC configuration mode.

Verifying the Configuration

To verify the configuration, perform the following steps.

SUMMARY STEPS

1. enable

2. show policy-map interface [interface-name]

3. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

show policy-map interface [interface-name]

Example:

Router# show policy-map interface atm1/0

Displays the packet statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface.

Enter the interface name.

Step 3 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

Configuration Examples for QoS: ATM-Based CLP Queue Limit

This section provides the following configuration examples:

Setting the Queue Limit: Examples

Verifying the Configuration: Examples

Setting the Queue Limit: Examples

In the following example, a policy map called "POLICY-ATM" has been configured. The POLICY-ATM policy map contains a class called "CLASS-ATM". The bandwidth for this class is specified as a percentage (20) and the queue-limit command sets the global queue-limit threshold to 1000 cells. The queue-limit atm clp command sets the queue-limit threshold for ATM CLP data to 100 cells.

Router> enable
Router# configure terminal
Router(config)# policy-map POLICY_ATM
Router(config-pmap)# class CLASS-ATM
Router(config-pmap-c)# bandwidth percent 20
Router(config-pmap-c)# queue-limit 1000 cells
Router(config-pmap-c)# queue-limit atm clp 100 cells
Router(config-pmap-c)# exit

In the following example, which is an L2VPN configuration, a policy map called "output_policy" has been configured. The output_policy uses the class-default classification. No bandwidth has been configured. The queue-limit command sets the global queue-limit threshold to 1000 cells. The queue-limit atm clp command sets the queue-limit threshold for ATM CLP data to 500 cells.

Router> enable
Router# configure terminal
Router(config)# policy-map output_policy
Router(config-pimp)# class class-default
Router(config-pmap-c)# queue-limit 1000 cells
Router(config-pmap-c)# queue-limit atm clp 500 cells
Router(config-pmap-c)# exit

Verifying the Configuration: Examples

The following example, which is from an L2VPN ATM configuration, shows an output policy map, class-default classification, global queue-limit threshold of 1000 cells, and a CLP queue-limit threshold of 500 cells.

Router# show policy-map

   Policy Map output_policy
    Class class-default
      queue-limit 1000 cells
      queue-limit atm clp 500 cells

Router# show running interface ATM3/3

  interface ATM3/3
  pvc 7/101 l2transport
    encapsulation aal0
    xconnect 11.11.11.11 7101 encapsulation mpls
    service-policy out output_policy

The following example, which is from an L2VPN ATM configuration, shows statistics that include all the policy maps attached to ATM interface 3/3 and VC 7/101.

Router# show policy-map interface a3/3 vc 7/101
  ATM3/3: VC 7/101 -


  Service-policy output: output_policy (1057)


    Class-map: class-default (match-any) (1058/0)
      206084 packets, 10716368 bytes
      5 minute offered rate 245000 bps, drop rate 0 bps
      Match: any  (1059)
      Tx queue-limit config
      Queue 0: queue-limit 1000 cells
      Queue 0: queue-limit atm clp 500 cells
      Threshold drop 0 packets, 0 bytes
      Current queue-depth: 21 cells, Maximum queue-depth: 1023 cells

Additional References

The following sections provide references related to the QoS: ATM CLP-Based Queue limit feature.

Related Documents

Related Topic
Document Title

Quality of service (QoS) commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco IOS Quality of Service Solutions Command Reference, Release 12.3T

Congestion-avoidance mechanisms, including tail drop, RED and WRED

Congestion Avoidance Overview, Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.3

Congestion-management mechanisms, including CBWFQ and DCBWFQ

Congestion Management Overview, Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.3

Byte-based WRED

Byte-Based Weight Random Early Detection feature module, Cisco IOS Release 12.0(26)S


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.


Technical Assistance

Description
Link

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/public/support/tac/home.shtml


Command Reference

This section documents a new command. All other commands used with this feature are documented in the Cisco IOS Release 12.3 command reference publications.

queue-limit atm clp

queue-limit atm clp

To specify the maximum size (in cells, microseconds, or milliseconds) of a queue for a specific traffic class, use the queue-limit atm clp command in policy-map class configuration mode. To remove the queue limit atm cell loss priority (clp) value from a class, use the no form of this command.

queue-limit atm clp queue-size {cells | ms | us}

no queue-limit atm clp

Syntax Description

queue-size

Threshold value. The range is 1-262144.

cells | ms | us

Unit of measure for the queue size; ms = milliseconds; us = microseconds.


Defaults

No default behavior or values

Command Modes

Policy-map class configuration

Command History

Release
Modification

12.0(30)S

This command was introduced.


Usage Guidelines

You can use the queue-limit atm clp command only with other queuing features, such as weighted fair queuing (WFQ). WFQ creates a queue for every class for which you define a class map. You can apply the policy map that you created with the atm clp based queue-limit command only to ATM interfaces on Cisco 12000 Series Routers.

Use the queue-limit atm clp command only after you have issued the queue-limit command using the same traffic class.

Use the no queue-limit command to remove both the global queue-limit queue-size value and the queue-limit atm clp queue-size value if you configured it.

Packets satisfying the match criteria for a class accumulate in the queue reserved for the class until they are sent, which occurs when the queue is serviced by the weighted fair queuing process. When the defined maximum packet threshold for the class is reached, enqueuing of additional packets to the class queue causes tail drop.

You can specify the CLP queue-limit threshold in cells, milliseconds (ms), or microseconds (us). However, the unit of measure cannot be mixed. For example, if you specify the CLP queue-limit threshold in milliseconds, then you must also specify the global queue-limit threshold in milliseconds.


Note When you specify the queue-limit threshold as cells, milliseconds, or microseconds, it is internally converted to cells by using the visible bandwidth that is available to the class or the ATM virtual circuit (VC).


Examples

In the following example, a policy map called "POLICY-ATM" has been configured. The "POLICY-ATM" policy map contains a class called "CLASS-ATM". The bandwidth for this class is specified as a percentage (20), and the queue-limit command sets the global queue-limit threshold to 1000 cells. The queue-limit atm clp command sets the queue-limit threshold for ATM CLP data to 100 cells:

Router> enable
Router# configure terminal
Router(config)# policy-map POLICY_ATM
Router(config-pmap)# class CLASS-ATM
Router(config-pmap-c)# bandwidth percent 20
Router(config-pmap-c)# queue-limit 1000 cells
Router(config-pmap-c)# queue-limit atm clp 100 cells
Router(config-pmap-c)# exit

Related Commands

Command
Description

bandwidth (policy-map class)

Specifies or modifies the bandwidth allocated for a class belonging to a policy map.

class class-default

Specifies the default traffic class whose bandwidth is to be configured or modified.

class (policy-map)

Specifies the name of the class whose policy you want to create or change, and the default class (commonly known as the class-default class) before you configure its policy.

policy-map

Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.

queue-limit

Specifies or modifies the maximum number of packets the queue can hold for a class configured in a policy map.


Glossary

CLP—cell loss priority. A field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Cells with CLP=0 are ensured traffic, which is unlikely to be dropped. Cells with CLP=1 are best-effort traffic, which might be dropped in congested conditions to free up resources to handle ensured traffic.

DCBWFQ—distributed class-based weighted fair queuing. Distributed class-based weighted fair queueing extends the standard WFQ functionality to provide support for user-defined traffic classes.

policy map—Any defined rule that determines the use of resources within the network. A policy can be based on a user, a device, a subnetwork, a network, or an application. The policy map is used to create a traffic policy.

tail drop—A means of avoiding congestion that treats all traffic equally and does not differentiate between classes of service (CoS). Queues fill during periods of congestion. When the output queue is full and tail drop is in effect, packets are dropped until the congestion is eliminated and the queue is no longer full.

threshold—The maximum number of packets that a queue can hold.

traffic class—A traffic class is used to classify traffic. A traffic class contains three major elements: a name, a series of match commands, and, if more than one match command exists in the traffic class, an instruction on how to evaluate the match commands.

traffic policy—A traffic policy is to configure the QoS features that should be associated with the traffic that has been classified in a user-specified traffic class or classes.

WFQ—weighted fair queuing. A congestion-management algorithm that identifies conversations (in the form of traffic streams), separates packets that belong to each conversation, and ensures that capacity is shared fairly between these individual conversations. WFQ is an automatic way of stabilizing network behavior during congestion and results in increased performance and reduced retransmission

WRED—weighted random early detection. A queuing method that ensures that high-precedence traffic has lower loss rates than other traffic during times of congestion.


Note Refer to Internetworking Terms and Acronyms for terms not included in this glossary.