Table Of Contents
High Priority Traffic Jitter Improvement Feature Overview
Latency Variation (Jitter) Calculation
Related Features and Technologies
Supported Standards, MIBs, and RFCs
Configuring High Priority Traffic Jitter Improvement
Monitoring High Priority Traffic Jitter Improvement
High Priority Traffic Jitter Improvement for Cisco 12000 Series Router, Cisco 12000 SIP-400, Shared Port Adapters
Part Number: OL-8685-01 (Rev. A0) November 16, 2007
Feature History
12.0(32)S
This feature was introduced on the Cisco 12000 series router, Cisco 12000 SIP-400, Shared Port Adapters (SPAs).
This feature module provides information on High Priority Traffic Jitter Improvement in the following sections:
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High Priority Traffic Jitter Improvement Feature Overview
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High Priority Traffic Jitter Improvement Feature Overview
The High Priority Traffic Jitter Improvement feature reduces latency variation (jitter) on the Cisco 12000 SIP-400, Shared Port Adapters (SPAs) by separating back pressure signaling from the SPAs towards the queuing ASIC for high and low priority traffic. This mechanism ensures that high priority traffic will not be delayed by congesting low priority traffic. The independent back pressure signaling is effected by separating out the high priority and low priority traffic into independent ports on the queuing ASIC—one for each.
Note
Latency Variation (Jitter) Calculation
The High Priority Traffic Jitter Improvement feature limits worst case latency variation (jitter) to the sum of all of the following calculations:
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The following example shows the worst case calculation for:
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Fragment line delay: 128 * 8 / 128000 = 8 msHDLC controller back pressure threshold for HP traffic delay: 128 * 8 / 128000 = 8 msEngine queuing delay: 72 * 1 * 8 / 128000 = 4.5 msEgress queuing ASIC port scheduling delay: 4 msEgress queuing ASIC token refill delay: 0.5 msMax jitter: 8 ms + 8 ms + 4.5 ms + 4 ms + 0.5 ms = 25 ms
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Benefits
The High Priority Traffic Jitter Improvement feature reduces latency and latency variation (jitter) for high priority traffic.
Cisco IOS Modular Quality of Service CLI configuration is backward compatible.
Restrictions
Scalability
For the L3nCnD QoS model, each Frame Relay subinterface configured with the High Priority Traffic Jitter Improvement feature requires 2 ports, which reduces by half the number of Frame Relay subinterfaces available when all Frame Relay subinterfaces are configured.
Related Features and Technologies
Cisco IOS Quality of Service (QoS) solutions for Cisco 12000 series routers
Related Documents
For information on configuring multicast traffic, refer to Cisco 12000 Series Router Configuration Guide for Cisco IOS Release 12.0S.
Also refer to the installation and configuration guide for a specific Cisco 12000 series router.
Supported Platforms
The High Priority Traffic Jitter Improvement feature is supported on the following Cisco 12000 series router, Integrated Services Engine (ISE), Shared Port Adapters (SPAs) running Cisco IOS Release 12.0(32)S:
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1CnD and nCnD QoS models are supported.
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.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported, and support for existing standards has not been modified.
MIBs
No new or modified MIBs are supported, and support for existing MIBs has not been modified.
RFCs
No new or modified RFCs are supported, and support for existing RFCs has not been modified.
Prerequisites
No prerequisites are required for this feature.
Configuration Tasks
See the following sections for configuration tasks for the High Priority Traffic Jitter Improvement feature.
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Configuring High Priority Traffic Jitter Improvement
This configuration procedure shows how to configure the High Priority Traffic Jitter Improvement feature for a Frame Relay subinterface on a 128 kbps channel line-rate, using a flat service policy.
In Step 2 :
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Step 1
Router#Router#config tRouter(config)#class-map match-any voice-ipRouter(config-cmap)#match ip dscp 63Router(config-cmap)#match ip precendence 7Router(config-cmap)#exitRouter(config)#Step 2
Router(config)#policy-map Low-Latency
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Router(config-pmap)#class voice-ipRouter(config-pmap-c)#priorityRouter(config-pmap-c#police cir 64000Router(config-pmap-c)#queue-limit 1Router(config-pmap-c)#exitRouter(config-pmap)#exitRouter(config)#Step 3
Router(config)#map-class frame-relay LFIRouter(config-cmap)#frame-relay fragment 128Router(config-cmap)#exitRouter(config)#Step 4
Router(config)#interface Serial2/0.1/1:0Router(config-if)#no ip addressRouter(config-if)#encapsulation frame-relayRouter(config-if)#exitRouter(config)#Step 5
Router(config)#interface Serial2/0.1/1:0.1Router(config-if)#ip address 2.1.1.1 255.255.255.0Router(config-if)#frame-relay interface-dlci 16Router(config-fr-dlci)#class LFIRouter(config-subif)#service-policy output Low-LatencyRouter(config-subif)#exit
Monitoring High Priority Traffic Jitter Improvement
Use the following show commands to monitor and troubleshoot High Priority Traffic Jitter Improvement.
Command Reference
No new or modified CLI commands were introduced for the High Priority Traffic Jitter Improvement feature in Cisco IOS Release 12.0(32)S.
Glossary
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