Whitepaper IP SLA: Jitter. plixer. International

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1 Whitepaper IP SLA: Jitter 1 plixer

2 Table of Contents Table of Contents Introduction IP SLA VoIP Measurement Tools Jitter Latency Packet Loss MOS ICPIF Score IOS Version Warning Steps to Configure the IP SLA Responder Enable IP SLA Responder Verification of Responder Status Steps to Configure Jitter IP SLA IP SLA Jitter Monitor # Availability Verification Create Monitor Specify Type Specify Tag Specify Frequency Specify Owner Specify Type of Service Enabling the IP SLA Jitter Monitor Schedule the Monitor to Start Verification of IP SLA Jitter Configuration Editing or Removing an IP SLA Monitor Troubleshooting IP SLAs Create IP SLA Reports with Denika Performance Trender Steps to create reports in Denika SNMP Performance Trender

3 Introduction This document will aid an administrator in creating IP SLA Jitter monitors on Cisco routers. It also discusses how to create IP SLA reports using the Plixer SNMP Performance Trender Denika. IP SLA VoIP Measurement Tools Maintaining a quality VoIP network is obtainable when appropriate monitors are put in place. An IP SLA Jitter Operation will enable the administrator to create several IP SLA measurement reports. These reports include but are not limited to: Jitter The IP SLA UDP jitter operation was primarily designed to diagnose network suitability for real-time traffic applications such as voice over IP (VoIP), video over IP, or real-time conferencing. Jitter means inter-packet delay variance. When multiple packets are sent consecutively from source to destination, (for example, 10 ms apart) and the network is behaving ideally, the destination should be receiving them 10 ms apart. If there are delays in the network (like queuing, arriving through alternate routes, and so on) the arrival delay between packets may be greater or less than 10 ms. Using this example, a positive jitter value indicates that the packets arrived greater 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. Latency In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. Packet Loss Packet loss is the discarding of data packets in a network when a device is overloaded and cannot accept any incoming data at a given moment. MOS The quality of transmitted speech is a subjective response of the listener. Each codec used for transmission of Voice over IP provides a certain level of quality. A common benchmark used to determine the quality of sound produced by specific codecs is MOS (Mean Opinion Score). With MOS, a wide range of listeners have judged the quality of voice samples sent using a particular codec, on a scale of 1 (poor quality) to 5 (excellent quality). The opinion scores are averaged to provide the mean for each sample. Note: MOS can only be accomplished with a jitter probe.

4 ICPIF Score The ITU standard G.11 specifies how to measure voice quality. This method dictates the quality of voice calls by calculating the ICPIF(impairment/calculated planning impairment factor). IOS-based gateways calculate the ICPIF value for every call and log it as part of the CDR record. An ICPIF value of zero for a call is a perfect score. This is often the target for VoIP networks. The range for this score will be 0 to 55. Note: MOS and ICPIF scores only apply to IP SLA with VoIP CODECS included. IOS Version Warning Some IOS versions support IP SLA operations with slightly different navigation or methods of creation. The overall methods for creating IP SLA operations are the same. The administrator may need to use the? command to apply the correct commands for that IOS. Steps to Configure the IP SLA Responder: When setting up an IP SLA Jitter Responder, the destination router needs to be configured to respond to the source router initiating the communication. This step is necessary to generate values for SNMP performance trending. Enable IP SLA Responder: Router (config)# ip sla monitor responder Router (config)# exit 4

5 Verification of Responder Status: Router# show ip sla monitor responder For more details on responder configuration see: Steps to configure Jitter IP SLA IP SLA Jitter Monitor # Availability Verification: Prior to creation, the administrator should verify that there are no other IP SLA Monitors scheduled with the same number. Existing IP SLA monitors can be viewed by entering the following command: Router# show ip sla monitor configuration Create Monitor: Once the administrator has identified an available number, for the IP SLA Monitor, the creation of the Jitter IP SLA Monitor can be performed. Enter config mode and proceed with the following steps. 5

6 Router (config)# ip sla monitor < > Specify Type: Once the monitor has been created, it is necessary to specify what type of monitor is being used. In this case, a Jitter probe (i.e. operation/monitor). A Jitter monitor is configured by entering the destination IP address and port number in the config below. If MOS and ICPIF scores are required than a codec must be specified. The advantage factor is a handicap that would account for normal degradation of communications and is required even if the value is zero. For more information on advantage factors, click on the Cisco link at the end of this section. There are many type options for an administrator to use. The configuration below would provide measurable statistics for IP SLA reports. Router (config-sla-monitor)# type jitter dest-ipaddr <host name or ip> dest-port <1-6555> codec <codec> advantage-factor <0-20> Specify Tag: A tag must be specified to generate a description for SNMP performance trending. A typical description would be: NY to CA Jitter or Core to Edge Jitter g711alaw codec Router (config-sla-monitor-jitter)# tag <description of IP SLA Monitor> Specify Frequency: The frequency of this monitor should be 00 seconds or less. Giving this monitor a smaller time value is acceptable; keeping in mind that increased frequency will create more overhead for the router. Router(config-sla-monitor-jitter)# frequency < > 6

7 Specify Owner: The administrator of this IP SLA Monitor should document a contact or a group to notify if any questions arise. Router (config-sla-monitor-jitter)# owner <person or group> Specify Type of Service: This line defines a type of service (ToS) byte in the IP header of an IP SLA operation. IP SLA Monitors emulate and keep statistics on traffic that is identical to the type of traffic the administrator needs to monitor. If the administrator needs to monitor traffic statistics that run through a specific QoS queue, it is necessary to specify the ToS value associated with that queue. If the ToS is not specified, the Jitter Operation will not include a QoS tag in the packet. The chart below is useful in determining which Diffserv or decimal to use for the ToS config line. 7

8 Router (config-sla-monitor-jitter)# tos <0-255> Enabling IP SLA Jitter Monitor: The next step is to exit configuration mode and return to exec mode in order to Schedule the IP SLA operation. Router (config-sla-monitor-jitter)# exit Schedule the Monitor to Start: Once the monitor configuration has been completed it must now be enabled. There are many variations on how to schedule IP SLA monitors. For the purpose of creating dependable reports, the administrator should start the monitor upon completion and keep it running, until it is no longer needed. Router (config)# ip sla monitor schedule < > start-time now life forever Verification of IP SLA Jitter Configuration: Once the IP SLA Monitor has been started, it will generate statistics on the first transaction between the source and destination. The administrator may run statistics on the new IP SLA monitor by entering: Router# show ip sla monitor statistics < > Note: One way delay requires time synchronization between source and destination routers. 8

9 A successful implementation will result in RTT, latency, jitter, packet loss values and a MOS Score displayed with a number of successes greater than zero. If a MOS Score is not displayed then it will be necessary to review the jitter configuration to see if there is an error in the setup of this monitor by running: Router#show ip sla monitor configuration < > Editing or Removing an IP SLA Monitor: If the administrator finds a problem with the monitor or would like to make a change in the monitor, the monitor must be removed and then recreated by repeating the process outlined in this document. To remove an IP SLA Monitor the command below may be used: Router (config)# no ip sla monitor < > Troubleshooting IP SLAs: If problems persist, try verifying firewall configurations, access lists, or other networking issues that may be interfering in the process. The administrator should also make sure that the current IOS version supports these IP SLA Operations. 9

10 Creating IP SLA Reports with Denika Performance Trender Once the IP SLA Monitor has been successfully created and scheduled, the administrator can create IP SLA Performance Reports like those above with the Denika SNMP Performance Trender. 10

11 Steps to create reports in Denika SNMP Performance Trender: 1) Download the free version at 2) Install Denika on a Windows server ) Log in to the web interface 4) Click on the discovery button in the Admin Tools Tab 5) Click on the Single Device button 6) Enter the IP Address and the SNMP Community string for the router currently being configured for SLA Reporting. (If the community string is not public the administrator may simply create a credential with the correct community string.) 7) Click on the View First button and select the reports to be created. (Follow the instructions on the screen if the reports options wanted are not listed.) 8) Wait minutes for the trends to show up and celebrate. If you would like assistance creating reports in Denika, feel free to contact us at , or at: For Cisco documentation on IP SLA VoIP Jitter and other IP SLA Operations see: 11