Jitter

Packets of voice information traveling across a network take varying amounts of time to go from one end to the other. This variation is referred to as "jitter". The receiving end of a VoIP voice call "buffers" packet information so it can be played as a smooth and unbroken stream of voice audio. The depth of jitter (measured in milliseconds) can and should be measured. Always be sure that jitter settings match the behavior of the network. Dropouts may occur if the setting is too low, and delays in the audio will occur if the setting is too high.

Latency

The total amount of time it takes for a packet of voice information to get from one end of the network to the other is called latency. Latency is also measured in milliseconds. A latency of 200 or more milliseconds can result in echo, especially if the connections at the receiving end are not all digital. A latency of more than 400 milliseconds results in both parties of the call constantly "interrupting" each other, then waiting for the other person to finish. This situation is simply not acceptable for even the most patient of callers.

Codecs

A codec is responsible for converting the analog voice signal of a phone call to digital packets of information - then converting them back to analog voice audio. There are many types of codecs available depending on available bandwidth and the quality of the audio that is desired. First determine the amount of voice data traffic you anticipate having, then choose the appropriate codec. The G.711 codec is widely used throughout North America and although it consumes up to 83 kB per second of bandwidth it provides toll-quality voice connections.

Configuration for Quality of Service (QOS)

The most complicated and difficult issue you will encounter will be how to successfully configure the network to handle both data and voice packets simultaneously. File downloads and other data transfers that occur at the same time as voice calls can easily interfere and even interrupt these voice conversations if the network is not configured properly.

It is the job of the routers to treat voice packet information in a special way. Without routers giving voice packets special treatment, they will almost always lose the battle when in direct competition with data packets. The configuration of routers to do this properly is called "Quality of Service", or QOS. There are four types of configurations of QOS. Each provide different levels of efficiency for handling voice and data traffic simultaneously.