Comments on 200 OK: Why won't anybody build far-end echo cancellation ...

I am using a VoIP provider along with a Snom 370 a...

2010-05-12T18:05:46.587-04:00

I am using a VoIP provider along with a Snom 370 and everything is great for me. The problem is the callee is hearing echo! That is the real problem with VoIP-PSTN.

I appreciate the Anonymous Posters' comments. ...

2010-04-26T15:36:19.528-04:00

I appreciate the Anonymous Posters' comments. The posting from April 23, 2010 6:02 AM helps reinforce my argument: more can be done in the handset to improve the user's experience.

To the commenter on April 26, 2010 3:25 PM: My blog doesn't have anything to do with "my IT guys" or my phone system. I *am* the IT guy, and I'm a consulting network designer for numerous Carrier VoIP networks around the US, Canada, and Caribbean.

The big question is: why should noise improvement be done in the network? Why shouldn't it be done in the endpoint?

Instead of complaining just ask your IT guys to ad...

2010-04-26T15:25:57.671-04:00

Instead of complaining just ask your IT guys to add a solution on the VoIP network. There are at least two commercial solutions for this: Ditech VQA platform and SoliCall PBXMate platform.

There are two types of echo control algorithms: ec...

2010-04-23T06:02:48.428-04:00

There are two types of echo control algorithms: echo cancellation and echo suppression. It is not possible to perform echo cancellation on a VoIP connection due to jitter. Echo cancelation cannot function after any jitter buffer since its algorithm requires a constant delay (i.e. no jitter) between sending its reference signal and receiving its corresponding echo. A jitter buffer guarantees no interruptions in the stream, but it does not guarantee a constant delay between reference signal and its corresponding echo signal.

Ditech VQA carries out echo cancelation on a jitter-free signal to cancel hybrid echo, and uses echo suppression to control the acoustic echo generated at the VoIP phone. Note it says *suppress* rather than *cancel*: “Ditech’s AEC feature suppresses a wide range of echo variances using algorithms based on talker energy levels and Weighted Acoustic Echo Path Loss (WAEPL) to effectively suppress acoustic echo and significantly improve voice quality.”

If the Ditech VQA echo control technology was integrated in a VoIP handset, it would work as follows:

- The echo cancellation algorithm, which in Ditech VQA product cancels hybrid echo, would be used to cancel acoustic echo in the VoIP handset.
- The echo suppression technology, which in Ditech VQA product cancels acoustic echo from the VoIP handset, would be used to cancel the hybrid echo.

The article should make this distinction: VoIP Echo Cancellation is NOT possible. VoIP Echo Suppression is possible.

The anonymous commenter doesn't explain why ec...

2010-04-22T11:45:21.515-04:00

The anonymous commenter doesn't explain why echo cannot be cancelled at the SIP phone. It's not self evident that Anonymous is correct. The echo canceller should be applied AFTER the jitter buffer has settled all the jitter that it can.

After all, how else could the Ditech VQA platform cancel significant echo ANYWHERE in the network?

Likewise, how does the Metaswitch PB4000/PB4500/PB5000 cancel echo? It functions as an endpoint, terminating VoIP and converting it to TDM.

The echo must be cancelled as close as possible to...

2010-04-22T11:40:17.557-04:00

The echo must be cancelled as close as possible to its source. In this case the echo canceller running on the VoIP phone cancels the acoustic echo generated at the VoIP phone, and provides an echo free signal to the far end. The PSTN line echo (generated due to the hybrid that converts 4-wire line into 2-wire line) cannot be cancelled at VoIP phone due to jitter. The echo must be cancelled by the central office of the PSTN side or the VoIP gateway before the jitter starts.