Tamas not only mod_portaudio.
In my case used one leg terminated to FXS gateway, other leg terminated to PSTN via ISDN PRI/E1 gateway.
Echo is observed for some calls. I think the echo is formed on the side of the subscriber connected to PSTN.
I counted that the echo comes back with a delay of 44-64 ms or more (more detail http://www.adaptivedigital.com/product/echo_cancel/echo_explain.htm).
Where:
  1. 20-30 ms - packetization time on a-leg
  2. ~1 ms - VoIP packet delivery
  3. ~ 1 ms - PSTN network signal delivery
  4. ~ 1 ms - PSTN network return signal delivery
  5. 20-30 ms - packetization time on ISDN PRI gateway
  6. ~1 ms - VoIP return RTP packet delivery
If FS will apply echo canceller then is required compensate 22-32 ms echo for each leg.

Sergey



On Sun, Apr 19, 2015 at 9:11 AM, Tamas Jalsovszky <jalsot@gmail.com> wrote:
On Sat, Apr 18, 2015 at 11:39 AM, Steve Underwood <steveu@coppice.org> wrote:
> Could you help me understand that prevents the use echo cancellation in FS
How would you expect to use echo cancellation in FS?
It could be useful with for example mod_portaudio, IMO

Regards,
   Jalsot
 
Regards,
Steve


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