Downloads |
 Feedback
|
Table Of Contents
QoS: ATM CLP-Based Queue Limit
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
Attaching the Policy Map to an Interface
Configuration Examples for QoS: ATM-Based CLP Queue Limit
Setting the Queue Limit: Examples
Verifying the Configuration: Examples
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
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
•
Prerequisites for QoS: ATM CLP-Based Queue Limit
•
•
•
•
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
Restrictions for QoS: ATM CLP-Based Queue Limit
•
•
•
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
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
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
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.
2.
3.
4.
5.
Note
6.
7.
8.
DETAILED STEPS
Attaching the Policy Map to an Interface
To attach the policy map to an interface, perform the following steps.
Note
SUMMARY STEPS
1.
2.
3.
4.
5.
6.
DETAILED STEPS
Verifying the Configuration
To verify the configuration, perform the following steps.
SUMMARY STEPS
1.
2.
3.
DETAILED STEPS
Configuration Examples for QoS: ATM-Based CLP Queue Limit
This section provides the following 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> enableRouter# configure terminalRouter(config)# policy-map POLICY_ATMRouter(config-pmap)# class CLASS-ATMRouter(config-pmap-c)# bandwidth percent 20Router(config-pmap-c)# queue-limit 1000 cellsRouter(config-pmap-c)# queue-limit atm clp 100 cellsRouter(config-pmap-c)# exitIn 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> enableRouter# configure terminalRouter(config)# policy-map output_policyRouter(config-pimp)# class class-defaultRouter(config-pmap-c)# queue-limit 1000 cellsRouter(config-pmap-c)# queue-limit atm clp 500 cellsRouter(config-pmap-c)# exitVerifying 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-mapPolicy Map output_policyClass class-defaultqueue-limit 1000 cellsqueue-limit atm clp 500 cellsRouter# show running interface ATM3/3interface ATM3/3pvc 7/101 l2transportencapsulation aal0xconnect 11.11.11.11 7101 encapsulation mplsservice-policy out output_policyThe 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 7/101ATM3/3: VC 7/101 -Service-policy output: output_policy (1057)Class-map: class-default (match-any) (1058/0)206084 packets, 10716368 bytes5 minute offered rate 245000 bps, drop rate 0 bpsMatch: any (1059)Tx queue-limit configQueue 0: queue-limit 1000 cellsQueue 0: queue-limit atm clp 500 cellsThreshold drop 0 packets, 0 bytesCurrent queue-depth: 21 cells, Maximum queue-depth: 1023 cellsAdditional References
The following sections provide references related to the QoS: ATM CLP-Based Queue limit feature.
Related Documents
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
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
—
Technical Assistance
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
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
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
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> enableRouter# configure terminalRouter(config)# policy-map POLICY_ATMRouter(config-pmap)# class CLASS-ATMRouter(config-pmap-c)# bandwidth percent 20Router(config-pmap-c)# queue-limit 1000 cellsRouter(config-pmap-c)# queue-limit atm clp 100 cellsRouter(config-pmap-c)# exitRelated Commands
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
Copyright © 2004 Cisco Systems, Inc. All rights reserved.
