I’ve had many customers ask, “What is VoIP jitter and how does it apply to NetFlow?” so today we’re going to dive into this topic. If you’re a VoIP phone system administrator, I’m sure you’ve had those dreaded calls from your users yelling about poor call quality, so you check your bandwidth usage graphs, but you can’t find any network congestion. Now what?
What is VoIP Jitter?
VoIP is a real-time protocol (RTP) so there are many factors that can affect call quality as your phone traffic is traversing through the Internet.
In Cisco’s words, “Jitter is defined as a variation in the delay of received packets. At the sending side, packets are sent in a continuous stream with the packets spaced evenly apart. Due to network congestion, improper queuing, or configuration errors, this steady stream can become lumpy, or the delay between each packet can vary instead of remaining constant. ”
This means that the more VoIP jitter there is the more times you’ll be asking, “Can you hear me now?”
Troubleshooting VoIP jitter
In the past, network administrators have been able to view VoIP jitter with SNMP to see if a network device was experiencing jitter, but you couldn’t tell on a per phone call basis who was experiencing jitter. With advances in NetFlow and IPFIX you can now get Cisco Performance Monitoring jitter reports, SonicWALL jitter reports, and nProbe jitter reports on a per phone call basis. This means that when an angry customer calls in complaining about poor call quality, you can troubleshoot phone quality at each hop to see where VoIP jitter was introduced.
In the report below, on our Internet facing router, we can see that one of our remote employes has experienced some VoIP jitter today when making phone calls. Very quickly from this report I can see that the DSCP value, also known as quality of service, was set to zero, which means there was no quality of service, before the traffic was sent to him, which is likely a cause of VoIP jitter. I’m sure our network administrator heard about this.
Contact us if you have any questions about configuring NetFlow and IPFIX VoIP jitter reports and we would be glad to help!