Factors Affecting Voice Quality.

Voice quality depends on four main factors, Bandwidth, Delay, Packet loss and Jitter.

Bandwidth - Usually measured as the number of bits transferred per second. VoIP requires anywhere from about 24kbits per second up to about 90kbits per second. Bandwidth is rarely an issue if you are running Cable, DSL or Fiber.

Delay- Usually measured in milliseconds. Obviously the longer the delay the more difficult a conversation becomes. Anything under 100ms is good. The ITU recommend that one way delay should not exceed 400ms for acceptable speech quality.

Packet Loss - Usually measured as a percentage. Since your voice is being transmitted digitally over the internet it will be broken down into segments. These segments become the packets that are actually transmitted. A packet loss of up to four or 5% will go largely unnoticed. Anything above that and call quality will drop.

Jitter - Jitter when applied to VoIP is a variation in packet transit delay. The causes of jitter are typically queuing, contention and serialization effects on the path through the network. Faster, higher bandwidth networks tend to have less jitter whereas slower networks tend to have more congestion and more jitter. A QoS device like an ATA can help eliminate some of this jitter.

All of the above factors are taken into account in the summary you get at the end of the test.

For an in depth technical view on how your voice is digitized and transmitted by way of the internet read our series of technical blogs.