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Troubleshooting VoIP echo problems

How to determine a solution to echos in VoIP.


Troubleshooting VoIP echo problems
Tom Lancaster

Echo in VoIP networks is pretty common and as long as it is reasonably quiet and short most people can tolerate it, if they notice it at all. However, as the time between your speech and the echo grows, echoes quickly become unbearable.

The first step is to find the echo source. This is usually easier than you might think because in most cases, only one party hears the echo. In such a case, the echo source is always on the far end. This is fairly logical if you think about standing in a canyon shouting "echo echo echo". If you stand right next to a wall and shout "echo" you're not going to hear one. In order to hear the echo, you have to stand far enough away so that the sound has time to travel from you to the "source" and bounce back to you. When you shout "echo" into a nearby wall, more sound bounces back to you, but the delay is so short that you can't hear it. For this reason, if your local gateway is causing an echo (which it very well may be), you won't hear it because you're too close.

After you figure out which end of the circuit is causing the echo, look for the "usual suspects". The easy bet is cheap headsets or conference phones. These devices are notorious for allowing the output from the speaker back into the input (the microphone). This is easy because you can swap them out immediately and tell if the echo disappears. If it doesn't, the next guess is any place where different telephony technologies meet. For instance, a 2-wire to 4-wire conversion and a digital to analog gateway are common causes of noticeable echo. Troubleshooting these components will take a little more effort and usually some testing instruments to measure things like decibel loss and impedance.

Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.

This was last published in November 2001

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