Q

Solving echo and lag for call recipient

In this expert response, Patrick Ferriter explains why a call recipient might experience echo. He explains the two main sources of echo in telephony networks and and how to fix the issue.

When initiating a VoIP call I hear no echo or lag. The person I'm calling does. Any ideas?

There are two main sources of echo in telephony networks: line echo and acoustic echo. Acoustic echo is generated

on any phone (IP or otherwise) when there is feedback from the speaker to the microphone. This is particularly noticeable on many speaker phones. Line echo is very common in the PSTN network and this most commonly occurs when there is a two wire to four wire conversion in the network (for example, where analog is converted into T1 or E1).

To combat these types of echo, there are echo cancellers. As you can probably imagine there are acoustic echo cancellers (AEC) and line echo cancellers (LEC). How well the echo is cancelled depends upon the quality of the echo canceller. One key parameter in an echo canceller is the tail length. Basically, the way an echo canceller works is it remembers the waveform sent out, and for a certain period of time looks to see a waveform coming back that it can correlate to the original signal (usually arriving later, at lower amplitude, and with more noise). Typically, echo cancellers can be set to 32ms, 64ms, or 128ms tail lengths. If the return signal (echo) arrives too late, the echo canceller won't be able to properly correlate and cancel it. In summary, it is possible to greatly minimize or nearly eliminate echo if proper echo cancellation is in place.

It is possible that your VoIP device has an AEC that is not performing well. Sometimes a poor quality headset can also introduce echo that the far end can hear. It is a good idea to report the problem to your VoIP service provider and explain the symptoms. If your VoIP device will allow you to lower the receive gain or volume, this may also help to reduce the level of the echo the called party hears.

This was first published in August 2005

Dig deeper on VoIP QoS and Performance

Pro+

Features

Enjoy the benefits of Pro+ membership, learn more and join.

Have a question for an expert?

Please add a title for your question

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

0 comments

Oldest 

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

SearchMobileComputing

SearchNetworking

SearchTelecom

SearchITChannel

SearchEnterpriseWAN

SearchExchange

Close