VOIP.com - Internet Phone Service

voip.com Internet Phone Service

VoIP > Blog

Voip Blog

Latency and VoIP Call Quality

Tuesday, April 22, 2008

Back when I was a kid in the 1980s, there was a time when I lived in California and my mom lived in Hawaii. In those days, calls between Hawaii and the mainland went over the satellite. This meant there was, at minimum, a half-second delay--complete with a bit of echo.

A couple of decades later, that problem is but a distant memory. Fiber optics runs between the mainland and the Hawaiian islands, making calls sound like they're right next door. The echo and delay are gone.

What I experienced on those calls to Hawaii as a kid is something you might experience on a VoIP call--latency. In short, it's the amount of time it takes your voice to reach the other end of the connection. What's reasonable? 150 milliseconds. Anything over 300 milliseconds and the voice quality deteriorates.

This is one reason why VoIP on dialup is typically not supported. Dialup involves round-trip packet times of at least 300-350 milliseconds, and that's before it even gets to the Internet! When you add the round-trip time to a site on the Internet, the round-trip times can start approaching what I experienced with the calls traveling over satellite.

In order to achieve latency figures around 150 milliseconds, the following things must occur: the sender's voice has to be encoded into IP, sent out over the network, arrive at the service provider, be sent to the receiving party, received by the receiving party, decoded and played for the receiving party.

While some of the latency can be controlled by the providers--namely stuff that happens within their network--a large chunk of the latency occurs between you and the provider over your public Internet connection. Variations in the latency and packet loss can play a huge role in how your VoiP calls sound.