[asterisk-dev] Adding Octastic Soft-Echo to external SIP adapters

[Steven Critchfield]

On Fri, 2007-05-04 at 14:00 -0400, syd wonder wrote:
> Hi all.  I'm trying to hook into a chan_zap.c function that enables echo 
> cancellation.  I think I've identified the spots to hook into but am 
> wondering if someone can answer a few questions or provide some guidance.
> 
> 1 - I'm using an external device (Sipura SPA3000 FXS/FXO) configured as a 
> SIP trunk.  I'm hoping  that along with the Chan_Sip.C file, that the 
> Chan_Zap.c file is used to setup some of the functionality, namely - whether 
> echo cancellation should be enabled
> 2 - With item 1 being true, the reason why echo cancelling is not being 
> enabled is because the external device is being recognized as a digital 
> channel.
> 
> Anyone have a suggestion as to whether these assumptions are true?  If not, 
> any suggestions how I can add the echo cancellation functions to non-zap 
> devices.  This is something a bit more interesting now that Octastic has 
> released their SoftEcho software.   Thanks.. Syd

First, I think the echo cancelling is done in the zaptel kernel module.
Echo cancelling is very time dependent and shouldn't be done over a
variable latency interface.

Chan_sip would expect that the echo cancelling was done on the SIP
device itself, and any other interface would have done the same. 

As I understand it, echo canceling is supposed to be done on the
listening side. You selectively remove portions of sent audio from the
received audio to eliminate echo. 

So to identify your echo, is it on the FXS/FXO port of your SPA, then it
should be the SPAs duty to handle the echo canceling, I think.
-- 
Steven Critchfield <critch at basesys.com>