What Does Jitter Tell You About VoIP Quality?

The quality of VoIP phone calls can be affected by various factors. When your phone quality suffers, it’s hard to pinpoint the exact location of the problem because the different factors can affect one another. This being said, the most important thing you can to do ensure smooth service is to configure your QoS settings to give VoIP priority over all other types of traffic. Once this is specified, there are two ways to determine the overall performance level of your service. These are latency and jitter.

Latency
This is the term given to the time delay that occurs when voice packets move from their original source to the destination. If this number is more than 150ms, voice quality could suffer. If some of the call travels across the public Internet, causing additional latency, a company’s internal latency will also suffer.

Jitter
The variability of these packet delays is called jitter. This variability is caused by the simple fact that each packet might take a different route to reach its final destination. If certain packets take longer than others, packets may be received in a different order than they were sent, or may get lost entirely on the way. Jitter in excess of 40ms will cause a serious decline in voice quality. High jitter levels are usually due to congested networks or slow Internet speed.

Measuring Jitter
There are several ways to measure jitter. The three types of measurement are Mean absolute packet delay variation, Mean packet to packet delay variation, and Packet delay variation histograms. Depending on the chosen method, different parameters or assumptions will be used. Because jitter measurement is an important part of effective VoIP phone service, many vendors list average jitter values as part of their SLAs.

Compensating for Jitter
1. Check your QoS settings to make sure voice packets receive priority.
2. Use a jitter buffer which allows the receiving device to store packets and realign them later.
3. Consult experts to identify the source of network jitters in order to combat them.