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Echo cancellation revisited: Identify and eliminate the root cause of delay

Prompted by a reply to an earlier response, unified communications strategies expert Matt Brunk discusses how to cancel echo when delay is significantly impacting voice quality.

If the delay is greater than 128 milliseconds (msec), no standard echo cancellation will work. In such cases, how about doing server side echo cancellation, as offered by Ditech's Voice Quality Assurance (VQA) or SoliCall's PBXMate?

From the editor: A SearchUnifiedCommunications.com member recently submitted a question about background noise...

and echo issues in their 100-seat call center, which was answered in a step-by-step guide to identifying and resolving background noise and echo by our unified communications strategies expert, Matt Brunk.

After reading Matt's detailed expert answer, our member replied with a follow-up inquiry on how to cancel echo when delay runs up to 128 msec. Below, Matt's response.

Answer:
If the delay is over 128 msec, then the configuration/network design needs an initial assessment. Network assessments will look at the entire network holistically and enable you to avoid blindly throwing money at issues or merely putting Band-Aids on bigger problems.

Customers and even support staff often think that if their setup is small or does not handle a lot of traffic, they can easily assume that VoIP is going to work. Then a physical site survey offers an idea of what's going on, but the details must include the applications; even still, the true nitty-gritty details lie in the scientific analysis that is accomplished by running a qualified network assessment. This isn't inexpensive, but it usually is infinitely more effective and, in the long term, does cost less than trying to speculate how to resolve latency issues. Run the network assessment, take corrective actions and run the assessment again.

I want to repeat what I said before: You must identify the root source of the delay. You mentioned Ditech's VQA, another really cool solution -- let's read what Ditech says about VQA, and please note the company's caution (the underlined portion):

Measurements in live networks using test systems compliant with the emerging ITU-T G.160 specification show significant improvement in signal-to-noise ratio (SNR) and total noise reduction, well in excess of values recommended by G.160. These measurements correspond with the results of subjective user tests, proving the perceived voice quality is significantly improved with Ditech's VQA technology. § Ditech's VQA solutions are available in packages with features specific to network and application needs. Not all of the features that follow are available for all network applications.

Before you can even pursue the Ditech VQA platform, your network assessment and site survey will break down the network and its current performance, identifying where improvements are needed, and your site survey will address your network applications. You still can't justify buying a tool or technology as a cure when you haven't identified the root cause of the problem -- how will you know if the tool/technology is the right fit for your purpose?

This was last published in June 2010

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