[Asterisk-Dev] echo, delay and dropped packets in channel driver

[Kris Boutilier]

> -----Original Message-----
> From: asterisk-dev-bounces at lists.digium.com 
> [mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of Ben Kramer
> Sent: Wednesday, November 02, 2005 3:37 PM
> To: asterisk-dev at lists.digium.com
> Subject: [Asterisk-Dev] echo, delay and dropped packets in 
> channel driver
> 
> 
> heya,
> 
{clip}
> 
> A decided to try and record the echo being heard, so added a 
> Monitor() command to the demo extens. What I see in the 
> record files is no echo, but I often see 20/40/60/80 ms gaps 
> of silence in both the in and out files.
> 

There is an issue present in both the mec2 and kb1 echo cancellers in
zaptel related to the echo can algorithm going a little nuts when it
gets a burst of '0' level samples. Similarly it also behaves poorly in
the presence of sustained very high signal levels. That being the case,
the echo artifacts you're hearing may be a symptom of the gaps in the
returning data coming in off of the pstn causing the can to generate,
rather than supress, echos. 

The MG2 canceller submitted by mgernoth (which is available for
evaluation right now - see http://bugs.digium.com/view.php?id=5520)
contains modifications specifically to fix these abhorrent behaviours.
Using it instead may aleviate the echo issues, though it won't remedy
the underlying problem.

Hope that helps.

Kris Boutilier
Information Services Coordinator
Sunshine Coast Regional District