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

[Ben Kramer]

On Wed, 2005-11-02 at 22:28 -0800, Kris Boutilier wrote:
> > -----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.

Actually, as its not a zaptel card, so it doesnt use the zaptel echo
cancellors. What I am trying to work out is the cause of the delay when
chan_vpb interacts with the ast bridge functions.

Cheers,

Ben.

> 
> Hope that helps.
> 
> Kris Boutilier
> Information Services Coordinator
> Sunshine Coast Regional District
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