Jitter and VoIP: Congestion on the line
Many companies use VoIP (Voice over Internet Protocol). But if a problem occurs during the transmission
of data packets, then this protocol is in danger of malfunctioning. One single delayed data packet can lead
to transmission errors and delays that are noticeable at once. Jitter can cause the audio signal to go down
or fill the line with static. With PRTG, you'll keep a constant eye on jitter values. If fluctuations occur, you can
quickly intervene to eliminate them. Jitter and VoIP go hand in hand. Along with jitter, you can also monitor
other parameters that affect the quality of your VoIP.
Some sensors to help you get started with jitter monitoring
How PRTG defines sensors
In PRTG, “sensors” are the basic monitoring elements. One sensor usually monitors one measured value in your network, e.g. the traffic of a switch port, the CPU load of a server, the free space of a disk drive. On average you need about 5-10 sensors per device or one sensor per switch port.
The PRTG QoS (Quality of Service) Round Trip sensor monitors the quality of your network connection. This sensor measures (or calculates) and displays jitter, latency, packet loss, and MOS (mean opinion score). The jitter value presents the minimum, maximum, and average deviations in milliseconds.
Cisco IP SLA sensor
Cisco devices (e.g. routers and switches) cause jitter to rise. Cisco IP SLA sensor uses SNMP to monitor the Cisco IP Service Level Agreement (SLA). This sensor is perfect for reading and displaying the jitter value.
Jitter tests: The why and the how
Running a jitter test
Create the above-mentioned sensors (e.g. the QoS (Quality of Service) Round Trip sensor). These sensors are preconfigured. There are no trial tests to run and you can read the jitter value directly from your network. PRTG comes with 100 free sensors that never expire. You can therefore test your network for jitter for free.
Individual jitter tests won't tell you much. The reason: They only check jitter for a specific point in time. When testing jitter, you’ll want to determine what is causing your jitter values to fluctuate. This can only be done via continuous and automated jitter monitoring.
Jitter is the deviation from the mean latency value, or the amount of time a data packet needs to reach its destination. It is measured in milliseconds (ms) and displayed in the sensor directly. A number of methods are used to measure jitter, including mean packet delay variation and mean absolute packet delay variation. PRTG complies with the standards of the RTCP for measuring jitter (RFC 1889). Learn more about how PRTG calculates jitter here.
The advantages of using PRTG to measure jitter
In companies that use VoIP, employees are unable to work unless the network is stable. Provide for optimal network stability by monitoring your VoIP with PRTG. By doing so, you’ll make sure your coworkers are able to work efficiently and without interruption.
PRTG stands out from other monitoring tools in that all its values are customizable. It immediately notifies you in the event of a problem, so you can react quickly – before noticeable interruptions or crashes arise. Thanks to PRTG, you’ll lift a huge weight off the shoulders of your support team, for fewer and fewer of your coworkers will have incidents to report.
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Practical tip: “Hey Stephan, do you have any tips for VoIP monitoring?”
“To simulate a telephone that uses the same network as your real IP telephone, simply set up our QoS Reflector Script on a Raspberry Pi and connect the latter to the desired point on the network. By doing so, you can guarantee that you are measuring the right network path with our QoS Round Trip Sensor. This is important because VoIP traffic is usually treated with priority.”
Stephan Linke, technical support at Paessler AG
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Jitter and latency: How to optimize your quality of service
How much time does a data packet need for its "trip” from the sender to the receiver? This time is referred to as latency. According to ITU-T, the agency responsible for telecommunications standards, latencies of up to 125 milliseconds are acceptable. PRTG’s recommendation: Set a threshold for 100 milliseconds. You’ll immediately receive an alert if this value is exceeded, allowing you to act quickly before noticeable interruptions or crashes arise.
Jitter measures the variation in a mean latency value. We recommend that this deviation be less than 20 to 25 milliseconds, even if this amount is somewhat lower than what is usually considered acceptable. The important thing is that you become aware of jitter as quickly as possible so you can take action at once. It also depends on your expectations: for some, jitter and delays of any kind are unacceptable.
Individual packets are often responsible for problems with VoIP. Packets can get lost or arrive as duplicates or in the wrong order. PRTG lets you identify each of these scenarios. We recommend setting your loss rate threshold at 0%, for just one lost packet can generate an error message or lead to a malfunction.
The short and sweet of it: All you need to know about jitter
What is jitter?
Data packets are transmitted at a certain speed. A sender sends packets to a receiver in millisecond intervals. Jitter occurs when this interval gets off track, leading to deviations or irregularities in runtime. The term "jitter” means fluctuation, oscillation, or a variation in frequency.
What happens if jitter is too high?
If data packets reach a receiver at irregular intervals, then loopholes emerge. As a result, data can no longer be circulated on a continual basis. While this may not be a big deal for web or email applications, it can cause interruptions in phone and video calls for companies who use VoIP. You’re also likely to encounter glitches at home when running real-time applications such as videos or computer games.
What causes jitter?
One example of how jitter can spike is when a data line is heavily strained, causing bottlenecks to appear in intermediate devices. In such a case, your available bandwidth is usually not sufficient (make a bandwidth test). High jitter can also be caused by data congestion in switches and routers. PRTG promptly alerts you if your hardware is overstrained, so you can intervene quickly – before your system malfunctions.
Bandwidth is measured as the amount of data that can be transferred from one point to another within a network in a specific amount of time. Typically, bandwidth is expressed as a bitrate and measured in bits per second (bps). It refers to the transmission capacity of a connection and is an important factor when determining the quality and speed of a network.
How do I eliminate jitter?
If jitter is high, then you may want to increase your bandwidth. Usually, however, this comes at an additional charge. As an alternative, you can give higher priority to VoIP than to other data packets, such as emails.
How is jitter calculated?
Jitter is calculated mathematically and in a standardized fashion. The IETF has outlined its jitter calculation method in RFC 3550. PRTG uses this protocol to calculate jitter.
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