Downloads |
Table Of Contents
PPP Session CAC Algorithm Improvements in RP
Restrictions for PPP Session CAC Algorithm Improvements
PPP Session CAC Algorithm Improvements in RP
Call Admission Control—Accept or Reject
Configuring PPP Session CAC Algorithm Improvements
Configuring CAC Based on CPU Utilization
Configuring CAC Based on Session Charges
Configuring CAC Charges Using a Session Charge Profile
Verifying and Monitoring CAC Operation
Example of No Configuration for CAC
Example of Verifying CAC Configuration
Example of CAC Operation Using the Original CAC Model
show call admission statistics
Feature Information for PPP Session CAC Algorithm Improvements in RP
PPP Session CAC Algorithm Improvements in RP
First Published: September, 2008This document describes improvements to the PPP session call admission control (CAC) algorithm in the route processor (RP).
Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for PPP Session CAC Algorithm Improvements in RP" section.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•
Restrictions for PPP Session CAC Algorithm Improvements
•
•
•
•
Restrictions for PPP Session CAC Algorithm Improvements
You should be familiar with the Call Admission Control operation and have a basic understanding of broadband aggregation.
•
•
•
PPP Session CAC Algorithm Improvements in RP
The Call Admission Control (CAC) feature allows a router to deny incoming calls, thereby protecting service provider network resources. Accepting too many calls might make the router inefficient in its operation, overloading both its own CPU and external peripherals such as a RADIUS server. The PPP Session CAC Algorithm Improvements in RP feature protects these resources of the router by enhancing the behavior of CAC operations.
In broadband networks, the broadband remote access system (BRAS) can scale to handle a high incoming rate of sessions. Each session that attempts to establish on the BRAS consumes the CPU and memory resources of the BRAS. If the BRAS uses external resources, such as RADIUS, to set up each session, RADIUS might not be able to handle all of the requests the router generates.
CAC aids the BRAS router in accepting calls by limiting the number of incoming calls based on either CPU or session charges. CAC protects the BRAS and external peripherals from getting overloaded by numerous requests that might come in during peak times.
The following sections describe the improvements to CAC operation in Cisco IOS Release 12.2(31)SB13:
•
Call Admission Control—Accept or Reject
In releases earlier than Cisco IOS Release 12.2(31)SB13, accepting or rejecting calls by Call Admission Control (CAC) is based on either of the following CAC models:
•
•
In Cisco IOS Release 12.2(31)SB13 and later releases, call acceptance and rejection are based on more granular resource checks. If resources are available, CAC accepts the call. The following describes how the route processor (RP) checks CPU utilization and session charges to determine call acceptance or rejection:
•
Note
•
Note
In releases earlier than Cisco IOS Release 12.2(31)SB13:
•
•
Note
Session Charge Improvements
CAC adds session charges per session type (for example, VPDN, PPPoE, PPPoA). These session charges last for a configurable lifetime. After the configured lifetime expires, the CAC operation decrements the charge.
In Cisco IOS Release 12.2(31)SB13 and later releases, the RP compares the existing outstanding session charges to the configured limit.
If the session charges are:
•
•
Platform Support
The PPP Session CAC Algorithm Improvements in RP feature is available on all Cisco routers with CAC, and in particular on high scaling aggregation routers such as the following:
•
•
•
Configuring PPP Session CAC Algorithm Improvements
To configure the PPP Session CAC Algorithm Improvements in RP feature, perform the following configuration tasks in the order presented:
•
•
•
•
Note
Enabling the New Model of CAC
To enable the new model of CAC in which improvements to the CAC algorithm protect the router's CPU and memory resources, use the following procedure.
SUMMARY STEPS
1.
2.
3.
DETAILED STEPS
Configuring CAC Based on CPU Utilization
To configure CAC based on CPU use, use the following procedure.
SUMMARY STEPS
1.
2.
3.
DETAILED STEPS
Configuring CAC Based on Session Charges
To configure CAC based on session charges, use the following procedure.
SUMMARY STEPS
1.
2.
3.
DETAILED STEPS
Configuring CAC Charges Using a Session Charge Profile
To configure CAC charges using a session charge profile, use the following procedure.
SUMMARY STEPS
1.
2.
3.
DETAILED STEPS
Configuration Example
The following configuration example configures a charge of 10 per session and a call admission limit of 50, which allows 5 calls per second (50/10) through the system:
Router(config)# call admission new-modelRouter(config)# call admission limit 50Router(config)# call admission pppoa 10 1Verifying and Monitoring CAC Operation
To verify and monitor CAC operation, use any of the following commands in privileged EXEC mode:
Verification Examples
This section provides the following examples of verifying CAC operation:
•
•
•
Example of No Configuration for CAC
The following example shows the information that appears when you enter the show call admission statistics command when CAC is not configured:
Router# show call admission statisticsCall Admission Control is not operational.Example of Verifying CAC Configuration
The following example shows the kind of information that appears when you enter the show call admission statistics command when CAC is configured:
Router# show call admission statisticsCAC New Model is ACTIVETotal call Session charges: 10, limit 20Total calls rejected 1576, accepted 306Reject reason: CPU-limit: 1000 Session Charges 576Current actual CPU: 3%, Limit: 20%Table 2 describes the fields in the output of the show call admission statistics command when CAC is configured and using the CAC new model.
Note
Example of CAC Operation Using the Original CAC Model
The following example shows sample output from the show call admission statistics command. In this example, the new CAC model is inactive, but CAC is configured and is using the original CAC model.
Router# show call admission statisticsCAC New Model (SRSM) is INACTIVE.Total call admission charges: 23, limit 20Total calls rejected 0, accepted 0Load metric: charge 23, unscaled 23%Table 3 describes the fields in the output of the show call admission statistics command when CAC is configured and using the CAC original model.
Additional References
The following sections provide references related to the PPP Session Call Admission Control Algorithm Improvements in the RP feature.
Related Documents
Standards
No new or modified standards are supported by this feature, and support for existing standards is not modified by this feature.
—
MIBs
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs is not modified by this feature.
—
Technical Assistance
Command Reference
The following commands are modified in the feature documented in this module. For information about all Cisco IOS commands, use the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or a Cisco IOS master commands list.
•
call admission
To configure the call admission control (CAC) charge for a call using a session charge profile, use the call admission command in global configuration mode. To disable this feature, use the no form of this command.
call admission type charge lifetime
no call admission type charge lifetime
Syntax Description
Defaults
This command has no default values or behavior.
Command Modes
Global configuration
Command History
Usage Guidelines
Cisco 10000 Series Router
In releases before Cisco IOS Release 12.2(31)SB, this command is a hidden command that determines the charge to add per call for a configurable time period. The charge values are set per-call type.
This command uses a session charge profile to determine call charges for CAC. The way in which the charge values are set depends on the CAC model that is enabled.
•
•
Examples
The following example shows how to use a PPPoA session charge profile to set call charges using the new CAC model:
Router(config)# call admission new-modelRouter(config)# call admission pppoa 10 1Related Commands
call admission cpu-limit
To configure the maximum CPU percentage at which call admission control (CAC) is to become active, use the call admission cpu-limit command in global configuration mode. To disable this feature, use the no form of this command.
call admission cpu-limit limit
no call admission cpu-limit limit
Syntax Description
Defaults
Inactive
Command Modes
Global configuration
Command History
Examples
The following example shows how to set the maximum CPU threshold for the new CAC. In this example, the CPU threshold is set for 80 percent.
Router(config)# call admission cpu-limit 80Related Commands
call admission limit
To define the maximum session charges allowed upon which the new call admission control model is to begin rejecting calls, use the call admission limit command in global configuration mode. To disable this feature, use the no form of this command.
call admission limit charge
no call admission limit charge
Syntax Description
Defaults
No default behavior or values
Command Modes
Global configuration
Command History
Usage Guidelines
Call Admission Control (New Model)
In Cisco IOS Release 12.2(31)SB13, this command determines the maximum outstanding session charges upon which the new CAC model is to begin rejecting calls. If the original CAC model is used, this command sets the maximum charge threshold, calculated using CPU, sessions, and buffer utilization.
If both the CPU load and session charges are above their thresholds, the call reject is counted against the CPU reason. The CPU load is always checked before the session charges.
Examples
The following example causes CAC to reject calls when the session charges reach a limit of 90,000:
Router(config)# call admission limit 90000Related Commands
call admission load
Configures a CAC metric for the CPU load.
show call admission statistics
Monitors the global CAC configuration parameters and the behavior of CAC.
call admission load
To configure a call admission control (CAC) metric for scaling WAN protocol session load or to configure a CAC metric for the CPU load, use the call admission load command in global configuration mode. To disable this feature, use the no form of this command.
call admission load multiplier metric-poll-rate
no call admission load multiplier metric-poll-rate
Syntax Description
Defaults
The default values are 100 for the multiplier and 1 for the poll rate. These values should not be changed without guidance from Cisco technical personnel.
Command Modes
Global configuration
Command History
12.3(2)T
This command was introduced.
12.2(31)SB13
This command was integrated into Cisco IOS Release 12.2(31)SB13 and implemented on the Cisco 10000 series router.
Usage Guidelines
This command enables CAC to limit overconsumption of Cisco IOS CPU cycles. On hardware-forwarded router platforms, established sessions tend not to consume much of the router processor resources, but there is a need to reduce resource utilization during session establishment, especially, to determine when a call cannot be handled and then to determine when it can be handled again.
For the call admission load command, the router load is calculated when software routines average the current CPU utilization. The command is configured as a mathematical formula—call admission load multiplier metric-poll-rate—where CPU utilization is polled every metric-poll-rate seconds and multiplied by a multiplier, which is the scaling factor. This formula results in a metric value for the current router load determined by existing sessions. The value is compared to that set for the call admission limit command, and if it exceeds the value, the call is rejected; otherwise, the call is accepted.
Note
Usage Guidelines for CAC Metric for CPU Load (Cisco 10000 Series Router)
The call admission load command is not used for the new CAC model.
The multiplier configuration is used to set the value to be added to the charge in the original CAC model at 100 percent load. Therefore, the command call admission load 150 1 means that if the CPU is 100 percent, the load charge is 150. If the CPU is 50 percent, the load charge is 75.
The metric poll rate is used to "damp" the CPU load charges, which means that you can save a couple of previous CPU loads and average them out over the metric-poll-rate number of times.
We recommend a value of 1 for the metric-poll-rate.
Examples
The following example shows recommended settings for the call admission load and call admission limit commands on the Cisco 10000 ESR:
Router(config)# call admission limit 90Router(config)# call admission load 100 1Related Commands
call admission new-model
To enable the new call admission control (CAC) model, use the call admission new-model command in global configuration mode. To disable this feature, use the no form of this command.
call admission new-model
no call admission new-model
Syntax Description
This command has no arguments.
Defaults
Disabled
Command Modes
Global configuration
Command History
Examples
The following example shows how to use a PPPoA session charge profile to set call charges using the new CAC model:
Router(config)# call admission new-modelRouter(config)# callRelated Commands
debug call-admission trace
To trace call admission control (CAC) operation and display debugging messages, use the debug call-admission trace command in global configuration mode. To turn off debugging of CAC, use the no form of this command.
debug call-admission trace
no debug call-admission trace
Syntax Description
This command has no arguments.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The debug call-admission trace command displays information about the operations of the original CAC model and of the new CAC model that was introduced in Cisco IOS Release 12.2(31)SB13.
The following describes the debugging messages that might display when you use the debug call-admission trace command:
session_charges now <session_charges>
Displays the current session charges after expirations.
Call charges added for session, curr.charges: <session_charges>
Displays the charges after the session commitment. The broadband component uses this to add session charges to the system.
Reject on session_charges (current <session_charges>)
Displays the reason CAC had to reject a session and displays the current session charges.
CAC enabled > session charges (<session_charges>/<configured session_charges limit>)
Displays when CAC is rejecting sessions because of session charges.
Reject on CPU charge (current <current cpu util>)
Displays the reason CAC has to reject a session based on the CPU charge and displays the actual current CPU utilization.
CAC enabled > CPU threshold (<current cpu util>/<configured cpu limit threshold>)
Displays when CAC is rejecting sessions because of CPU utilization.
CAC is no longer active, cpu/session charges are below thresholds:
CPU=<current cpu util>, Sess=<current session charges>
Displays when CAC is deactivated because the CPU and session charges are below the thresholds.
Examples
The following example shows how to use a PPPoA session charge profile to set call charges using the new CAC model:
Router(config)# debug call-admission traceRouter(config)#Related Commands
show call admission statistics
To monitor the global call admission control (CAC) configuration parameters and the behavior of CAC, use the show call admission statistics command in user EXEC or privileged EXEC mode.
show call admission statistics
Syntax Description
This command has no arguments or keywords.
Command Modes
User EXEC
Privileged EXECCommand History
Examples
The following is sample output from the show call admission statistics command for the original CAC model:
Router# show call admission statisticsTotal call admission charges: 0, limit 25Total calls rejected 12, accepted 51Load metric: charge 0, unscaled 0The load metric charge is computed using the following formula and is potentially damped with multiple values if the metric poll rate is greater than 1:
CPU_Load percent * Multiplier / 100
Table 4 describes the significant fields shown in the display.
Related Commands
Feature Information for PPP Session CAC Algorithm Improvements in RP
Table 5 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note
CCDE, CCENT, Cisco Eos, Cisco Lumin, Cisco Nexus, Cisco StadiumVision, Cisco TelePresence, the Cisco logo, DCE, and Welcome to the Human Network are trademarks; Changing the Way We Work, Live, Play, and Learn and Cisco Store are service marks; and Access Registrar, Aironet, AsyncOS, Bringing the Meeting To You, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, CCVP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Collaboration Without Limitation, EtherFast, EtherSwitch, Event Center, Fast Step, Follow Me Browsing, FormShare, GigaDrive, HomeLink, Internet Quotient, IOS, iPhone, iQ Expertise, the iQ logo, iQ Net Readiness Scorecard, iQuick Study, IronPort, the IronPort logo, LightStream, Linksys, MediaTone, MeetingPlace, MeetingPlace Chime Sound, MGX, Networkers, Networking Academy, Network Registrar, PCNow, PIX, PowerPanels, ProConnect, ScriptShare, SenderBase, SMARTnet, Spectrum Expert, StackWise, The Fastest Way to Increase Your Internet Quotient, TransPath, WebEx, and the WebEx logo are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries.
All other trademarks mentioned in this document or Website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0807R)
Any Internet Protocol (IP) addresses used in this document are not intended to be addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of IP addresses in illustrative content is unintentional and coincidental.
© 2008 Cisco Systems, Inc. All rights reserved.
