OER Voice Traffic Optimization Using Active Probes
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Table Of Contents
OER Voice Traffic Optimization Using Active Probes
Prerequisites for OER Voice Traffic Optimization Using Active Probes
Information About OER Voice Traffic Optimization Using Active Probes
OER Voice Traffic Optimization Using Active Probes
How to Configure OER Voice Traffic Optimization Using Active Probes
Identifying Traffic for OER Using a Prefix List
Identifying Voice Traffic to Optimize Using an Access List
Configuring OER Voice Probes with a Target Assignment
Configuration Examples for OER Voice Traffic Optimization Using Active Probes
Optimizing Only Voice Traffic Using Active Probes: Example
Optimizing Traffic (Including Voice Traffic) Using Active Probes: Example
Feature Information for OER Voice Traffic Optimization Using Active Probes
OER Voice Traffic Optimization Using Active Probes
First Published: August 14, 2006Last Updated: February 28, 2007This module documents an Optimized Edge Routing (OER) solution that supports outbound optimization of voice traffic based on the voice metrics, jitter and Mean Opinion Score (MOS). Jitter and MOS are important quantitative quality metrics for voice traffic and these voice metrics are measured using Optimized Edge Routing (OER) active probes.
OER provides automatic route optimization and load distribution for multiple connections between networks. OER is an integrated Cisco IOS solution that allows you to monitor IP traffic flows and then define policies and rules based on prefix performance, link load distribution, link bandwidth monetary cost, and traffic type. OER provides active and passive monitoring systems, dynamic failure detection, and automatic path correction. Deploying OER enables intelligent load distribution and optimal route selection in an enterprise network.
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 OER Voice Traffic Optimization Using Active Probes" 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
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Prerequisites for OER Voice Traffic Optimization Using Active Probes
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Prerequisites for OER Voice Traffic Optimization Using Active Probes
Before implementing OER optimization for voice traffic, you need to understand an overview of how OER works and how to set up OER network components. See the "Cisco IOS Optimized Edge Routing Overview" and "Setting Up OER Network Components" modules for more details. For a list of other OER configuration modules, see the "Where to Go Next" section and the "Related Documents" section.
Information About OER Voice Traffic Optimization Using Active Probes
Before you configure OER voice traffic optimization, you should understand the following concepts:
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Voice Quality on IP Networks
Voice packets traveling through an IP network are no different from data packets. In the plain old telephone system (POTS), voice traffic travels over circuit-switched networks with predetermined paths and each phone call is given a dedicated connection for the duration of the call. Voice traffic using POTS has no resource contention issues, but voice traffic over an IP network has to contend with factors such as delay, jitter, and packet loss, which can affect the quality of the phone call.
Delay
Delay (also referred as latency) for voice packets is defined as the delay between when the packet was sent from the source device and when it arrived at a destination device. Delay can be measured as one-way delay or round-trip delay. The largest contributor to latency is caused by network transmission delay. Round-trip delay affects the dynamics of conversation and is used in Mean Opinion Score (MOS) calculations. One-way delay is used for diagnosing network problems. A caller may notice a delay of 200 milliseconds and try to speak just as the other person is replying because of packet delay. The telephone industry standard specified in ITU-T G.114 recommends the maximum desired one-way delay be no more than 150 milliseconds. Beyond a one-way delay of 150 milliseconds, voice quality is affected. With a round-trip delay of 300 milliseconds or more, users may experience annoying talk-over effects.
Jitter
Jitter means interpacket delay variance. When multiple packets are sent consecutively from source to destination, for example, 10 ms apart, and if the network is behaving ideally, the destination should be receiving them 10 ms apart. But if there are delays in the network (like queuing, arriving through alternate routes, and so on) the arrival delay between packets might be greater than or less than 10 ms. Using this example, a positive jitter value indicates that the packets arrived more than 10 ms apart. If the packets arrive 12 ms apart, then positive jitter is 2 ms; if the packets arrive 8 ms apart, then negative jitter is 2 ms. For delay-sensitive networks like VoIP, positive jitter values are undesirable, and a jitter value of 0 is ideal.
Packet Loss
Packet loss can occur due an interface failing, a packet being routed to the wrong destination, or congestion in the network. Packet loss for voice traffic leads to the degradation of service in which a caller hears the voice sound with breaks. Although average packet loss is low, voice quality may be affected by a short series of lost packets.
Mean Opinion Score (MOS)
With all the factors affecting voice quality, many people ask how voice quality can be measured. Standards bodies like the ITU have derived two important recommendations: P.800 (MOS) and P.861 (Perceptual Speech Quality Measurement [PSQM]). P.800 is concerned with defining a method to derive a Mean Opinion Score of voice quality. MOS scores range between 1 representing the worst voice quality, and 5 representing the best voice quality. A MOS of 4 is considered "toll-quality" voice.
Probes Used by OER
OER uses some of the IP SLA probes to help gather the data OER requires to make its decisions.
Cisco IOS IP SLAs
Cisco IOS IP SLAs are an embedded feature set in Cisco IOS software and they allow you to analyze IP service levels for IP applications and services, to increase productivity, to lower operational costs, and to reduce occurrences of network congestion or outages. IP SLAs use active traffic monitoring—the generation of traffic in a continuous, reliable, and predictable manner—for measuring network performance. The accuracy of measured data is enhanced by enabling the IP SLAs Responder, available in Cisco routers, on the destination device. For more details about IP SLAs, see the Cisco IOS IP SLAs Configuration Guide.
Active Probe Types Used by OER
The following types of active probes can be configured:
ICMP Echo—A ping is sent to the target address. OER uses ICMP Echo probes, by default, when an active probe is automatically generated. Configuring an ICMP echo probe does not require knowledgeable cooperation from the target device. However, repeated probing could trigger an Intrusion Detection System (IDS) alarm in the target network. If an IDS is configured in a target network that is not under your control, we recommend that you notify the administrator of this target network.
Jitter—A jitter probe is sent to the target address. A target port number must be specified. A remote responder must be enabled on the target device, regardless of the configured port number.
TCP Connection—A TCP connection probe is sent to the target address. A target port number must be specified. A remote responder must be enabled if TCP messages are configured to use a port number other than TCP port number 23, which is well-known.
UDP Echo—A UDP echo probe is sent to the target address. A target port number must be specified. A remote responder must be enabled on the target device, regardless of which port number is configured.
Probe Frequency
In Cisco IOS Release 12.4(4)T and earlier releases, the frequency of an active probe used by OER was set to 60 seconds. In Cisco IOS Release 12.4(6)T and 12.2(33)SRB, the frequency can be increased for each policy by configuring a lower time-interval between two probes. Increased probe frequency can reduce the response time and provide a better approximation of the MOS-low count percentage
OER Voice Traffic Optimization Using Active Probes
OER voice traffic optimization provides support for outbound optimization of voice traffic on the basis of the voice performance metrics, delay, packet loss, jitter, and MOS. Delay, packet loss, jitter and MOS are important quantitative quality metrics for voice traffic, and these voice metrics are measured using OER active probes. In Cisco IOS Release 12.4(4)T and earlier releases, OER probes could measure delay and packet loss, but not jitter and MOS. The IP SLA jitter probe is integrated with OER to measure jitter (source to destination) and the MOS score in addition to measuring delay and packet loss. The jitter probe requires a responder on the remote side just like the UDP Echo probe. Integration of the IP SLA jitter probe type in OER enhances the ability of OER to optimize voice traffic. OER policies can be configured to set the threshold and priority values for the voice performance metrics: delay, packet loss, jitter, and MOS.
Configuring an OER policy to measure jitter involves configuring only the threshold value and not relative changes (used by other OER features) because for voice traffic, relative jitter changes have no meaning. For example, jitter changes from 5 milliseconds to 25 milliseconds are just as bad in terms of voice quality as jitter changes from 15 milliseconds to 25 milliseconds. If the short-term average (measuring the last 5 minutes) jitter is higher than the jitter threshold, the prefix is considered out-of-policy due to jitter. OER then probes all exits, and the exit with the least jitter is selected as the best exit.
MOS policy works in a different way. There is no meaning to average MOS values, but there is meaning to the number of times that the MOS value is below the MOS threshold. For example, if the MOS threshold is set to 3.85 and if 3 out of 10 MOS measurements are below the 3.85 MOS threshold, the MOS-low-count is 30 percent. When OER runs a policy configured to measure MOS, both the MOS threshold value and the MOS-low-count percentage are considered. A prefix is considered out-of-policy if the short term (during the last 5 minutes) MOS-low-count percentage is greater than the configured value for a given MOS threshold. OER then probes all exits, and the exit with the highest MOS value is selected as the best exit.
OER Forced Target Assignment
In Cisco IOS Release 12.4(4)T and earlier releases, the OER active probe target is assigned to the longest matched prefix. There are some scenarios where you may want to use a target that does not match the destination prefix. The example in Figure 1 explains a scenario in which configuring an OER forced target assignment is more appropriate than using the longest match prefix.
Figure 1 OER Forced Target Assignment Scenario
In Figure 1 we want to probe IP address 10.20.22.1 (at the edge of the network) for either network 10.20.21.0/24 or 10.20.22.0/24. Jitter is less likely to be introduced within the network so probing the edge of the network gives a measurement that is close to probing the final destination.
Forced target assignment allows you to assign a target to a group of prefixes or an application, even if they are not the longest match prefixes. Assigning a target can determine the true delay to the edge of a network rather than delay to an end host.
How to Configure OER Voice Traffic Optimization Using Active Probes
Configuring OER to optimize voice traffic using active probes involves several decisions and subsequent branching tasks. The first step is to identify the traffic to be optimized and decide whether to use a prefix list or an access list. Use a prefix list to identify all traffic, including voice traffic, with a specific set of destination prefixes. Use an access list to identify only voice traffic with a specific destination prefix and carried over a specific protocol.
The second step in optimizing voice traffic is to configure active probing using the active-probe or set active-probe command to specify the type of active probe to be used. In Cisco IOS Release 12.4(6)T and 12.2(33)SRB, the ability to set a forced target assignment for the active probe was introduced.
The final step in optimizing voice traffic is to configure an OER policy to set the performance metrics that you want OER to apply to the identified traffic.
Perform one of the first two optional tasks, depending on whether you want to use a prefix list or an access list to identify the traffic to be optimized. The third task can be used with traffic identified using an access list, and it also demonstrates how to use a forced target assignment. For an example configuration that can be used with traffic identified using a prefix list, see the "Optimizing Traffic (Including Voice Traffic) Using Active Probes: Example" section.
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Identifying Traffic for OER Using a Prefix List
Before traffic can be measured using OER, it must be identified. Perform this task to use a prefix list to identify the traffic that OER will probe.
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DETAILED STEPS
Identifying Voice Traffic to Optimize Using an Access List
Before voice traffic can be measured, it must be identified. Perform this task to use an access list to identify the voice traffic.
IP Protocol Stack for Voice
Voice traffic uses a variety of protocols and streams on the underlying IP network. Figure 2 is a representation of the protocol options available for carrying voice traffic over IP. Most signaling traffic for voice is carried over TCP. Most voice calls are carried over User Datagram Protocol (UDP) and Real-Time Protocol (RTP). You can configure your voice devices to use a specific range of destination port numbers over UDP to carry voice call traffic.
Figure 2 Protocol Stack Options Available for Voice Traffic
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DETAILED STEPS
Configuring OER Voice Probes with a Target Assignment
After identifying the traffic (in this example, voice traffic identified using an access list) to be optimized, perform this task to configure the OER jitter probes and assign the results of the jitter probes to optimize the identified traffic. In this task, the OER active voice probes are assigned a forced target for OER instead of the usual longest match assigned target. Before configuring the OER jitter probe on the source device, the IP SLAs Responder must be enabled on the target device (the operational target). The IP SLAs Responder is available only on Cisco IOS software-based devices. Start this task at the network device that runs the IP SLAs Responder.
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Prerequisites
Before configuring this task, perform the "Identifying Voice Traffic to Optimize Using an Access List" section.
SUMMARY STEPS
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DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
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ip sla monitor responder
Example:Router(config)# ip sla monitor responder
Enables the IP SLAs Responder.
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exit
Example:Router(config)# exit
Exits global configuration mode and returns to privileged EXEC mode.
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Move to the network device that is the OER master controller.
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enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 7
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
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oer-map map-name sequence-number
Example:Router(config)# oer-map TARGET_MAP 10
Enters OER map configuration mode to configure an OER map to apply policies to selected IP prefixes.
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match ip address {access-list access-list-name | prefix-list prefix-list-name}
Example:Router(config-oer-map)# match ip address access-list VOICE_ACCESS_LIST
References an extended IP access list or IP prefix as match criteria in an OER map.
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Step 10
set active-probe probe-type ip-address [target-port number] [codec codec-name]
Example:Router(config-oer-map)# set active-probe jitter 10.20.22.1 target-port 2000 codec g729a
Creates a set clause entry to assign a target prefix for an active probe.
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Step 11
set probe frequency seconds
Example:Router(config-oer-map)# set probe frequency 10
Creates a set clause entry to set the frequency of the OER active probe.
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Step 12
set jitter threshold maximum
Example:Router(config-oer-map)# set jitter threshold 20
Creates a set clause entry to configure the jitter threshold value.
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set mos {threshold minimum percent percent}
Example:Router(config-oer-map)# set mos threshold 4.0 percent 30
Creates a set clause entry to configure the MOS threshold and percentage values used to decide whether an alternate exit is be selected.
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set resolve {cost priority value | delay priority value variance percentage | jitter priority value variance percentage | loss priority value variance percentage | mos priority value variance percentage | range priority value | utilization priority value variance percentage}
Example:Router(config-oer-map)# set resolve jitter priority 1 variance 10
Creates a set clause entry to configure policy priority or resolve policy conflicts.
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set resolve mos priority value variance percentage
Example:Router(config-oer-map)# set resolve mos priority 2 variance 15
Creates a set clause entry to configure policy priority or resolve policy conflicts.
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set delay {relative percentage | threshold maximum}
Example:Router(config-oer-map)# set delay threshold 100
Creates a set clause entry to configure the delay threshold.
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exit
Example:Router(config-oer-map)# exit
Exits OER map configuration mode and returns to global configuration mode.
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oer master
Example:Router(config)# oer master
Enters OER master controller configuration mode to configure a router as a master controller.
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policy-rules map-name
Example:Router(config-oer-mc)# policy-rules TARGET_MAP
Applies a configuration from an OER map to a master controller configuration in OER master controller configuration mode.
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end
Example:Router(config-oer-mc)# end
Exits OER master controller configuration mode and enters privileged EXEC mode.
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show oer master active-probes [appl | forced]
Example:Router# show oer master active-probes forced
Displays connection and status information about active probes on an OER master controller.
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show oer master policy {sequence-number | policy-name | default}
Example:Router# show oer master policy TARGET_MAP
Displays policy settings on an OER master controller.
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Examples
This example shows output from the show oer master active-probes forced command. The output is filtered to display only connection and status information about the active probes generated for voice traffic configured with a forced target assignment.
Router# show oer master active-probes forcedOER Master Controller active-probesBorder = Border Router running this ProbePolicy = Forced target is configure under this policyType = Probe TypeTarget = Target AddressTPort = Target PortN - Not applicableThe following Forced Probes are running:Border State Policy Type Target TPort10.20.20.2 ACTIVE 40 jitter 10.20.22.1 305010.20.21.3 ACTIVE 40 jitter 10.20.22.4 3050What to do Next
For further configuration examples of OER voice traffic optimization, see the "Configuration Examples for OER Voice Traffic Optimization Using Active Probes" section.
Configuration Examples for OER Voice Traffic Optimization Using Active Probes
The following examples show both how to use an access list to identify only voice traffic to be optimized by OER and to use a prefix list to identify traffic that includes voice traffic to be optimized by OER.
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Optimizing Only Voice Traffic Using Active Probes: Example
Figure 3 shows that voice traffic originating at the remote office and terminating at the headquarters has to be optimized to select the best path out of the remote office network. Degradation in voice (traffic) quality is less likely to be introduced within the network, so probing the edge of the network gives a measurement that is close to probing the final destination.
Figure 3 OER Network Topology Optimizing Voice Traffic Using Active Probes
This configuration optimizes voice traffic to use the best performance path, whereas all other traffic destined to the same network—10.1.0.0/16—will follow the best path as indicated by a traditional routing protocol, for example BGP, that is configured on the device. As part of this optimization, OER will use policy based routing (PBR) to set the best exit link for voice traffic within a device.
The following configuration is performed on the edge router R1 in Figure 3 in the headquarters network to enable the IP SLAs Responder.
enableconfigure terminalip sla responderexitThe following configuration is performed on the edge router MC/BR (which is both an OER master controller and border router) in Figure 3 in the remote office network to optimize voice traffic using active probes.
enableconfigure terminalip access-list extended Voice_Traffic10 permit udp any 10.1.0.0 0.0.255.255 range 16384 32767exitoer-map Voice_MAP 10match ip address access-list Voice_Trafficset active-probe jitter 10.1.1.1 target-port 1025 codec g711alawset delay threshold 300set mos threshold 3.76 percent 30set jitter threshold 15set loss relative 5resolve mos priority 1resolve jitter priority 2resolve delay priority 3resolve loss priority 4Optimizing Traffic (Including Voice Traffic) Using Active Probes: Example
Figure 4 shows that traffic originating in the headquarters network and destined for the remote office network has to be optimized based on voice traffic metrics. Voice traffic is one of the most important traffic classes that travel from the headquarters to the remote office network, so the voice traffic must be prioritized to be optimized. Degradation in voice packet quality is less likely to be introduced within the network, so probing the edge of the network gives a measurement that is close to probing the final destination.
Figure 4 OER Network Topology for Optimizing All Traffic Using Active Probes
This configuration optimizes all traffic, including voice traffic, destined for the10.12.0.0/16 network. The OER optimization is based on the measurement of voice performance metrics with thresholding values using active probes. As part of the optimization, OER will introduce a BGP or a static route into the headquarters network. For more details about BGP and static route optimization, see the "Controlling the Traffic Class to Optimize and Verifying Network Performance Using OER" module.
The following configuration is performed on router R1 in Figure 4 in the remote office network to enable the IP SLAs Responder.
enableconfigure terminalip sla responderexitThe following configuration is performed on one of the BR routers in Figure 4 in the headquarters network to optimize all traffic (including voice traffic) using active probes.
enableconfigure terminalip prefix-list All_Traffic_Prefix permit 10.12.0.0/16oer-map Traffic_MAP 10match ip address prefix-list All_Traffic_Prefixset active-probe jitter 10.12.1.1 target-port 1025 codec g711alaw! port 1025 for the target probe is an example.set delay threshold 300set mos threshold 3.76 percent 30set jitter threshold 15set loss relative 5resolve mos priority 1resolve jitter priority 2resolve delay priority 3resolve loss priority 4Where to Go Next
This document describes a specific implementation of OER and presumes that you are familiar with the OER technology. If you want to review more information about OER, proceed to the Cisco IOS Optimized Edge Routing Overview module, followed by the Setting Up OER Network Components module. If you have set up your OER components, you should read through the other modules in the following list:
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After you understand the various OER phases, review the OER solutions modules that are listed under "Related Documents" section.
Additional References
The following sections provide references related to optimizing voice traffic using OER active probes.
Related Documents
Cisco OER technology overview
Concepts and configuration tasks required to set up OER network components.
OER solution module: configuring VPN IPsec/GRE tunnel interfaces as OER-managed exit links.
"Configuring VPN IPsec/GRE Tunnel Interfaces As OER-Managed Exit Links" module
Cisco OER commands: complete command syntax, command mode, command history, defaults, usage guidelines and examples
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IP Routing Protocol commands
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IP Routing Protocol configuration tasks
Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4
Technical Assistance
Feature Information for OER Voice Traffic Optimization Using Active Probes
Table 1 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Release 12.4(6)T, 12.2(33)SRB, or a later release appear in the table.
For information on a feature in this technology that is not documented here, see the "Cisco IOS Optimized Edge Routing Feature Roadmap."
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.
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Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2006-2007 Cisco Systems, Inc. All rights reserved.
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