[Freeswitch-users] echo cancellation on PRI cards

[David Knell]

Hi Arnaldo,

That's interesting - Brasil was my first proper IVR installation: one 
with Embratel in Sao Paulo, and then a couple with TeleRJ.  I remember 
landing at Sao Paulo airport for the first time at 7 a.m. with 
instructions to "meet a fat man called Ferrari" unsure as to whether I 
was in some sort of elaborate hoax (I wasn't, and he was), and learning 
my first three words of Portuguese as we left the car park: filho da 
puta, of course.

Those had no EC.  DTMF detection worked fine, and the audio quality of 
the IVR recordings was perfect, which is what you'd expect: EC doesn't 
alter the IVR->caller audio at all.  A TDM->SIP->TDM type application is 
a different animal: you've got the added latency of packetisation/jitter 
buffering/etc. which pretty much makes echo cancellation a must.

--Dave
> Sharing my humble experience: in Brazil we usually need echo 
> cancellation to have reliable DTMF detection _and_ voice quality over 
> E1 lines (be it on MFC/R2 - r2d - or ISDN PRI lines), either for 
> sip/tdm gateway devices or IVR applications.
>
> Usually there's no need for echo cancellation on links from some 
> Telcos, in some specific places. But we need it in the majority of 
> cases, even when my box is just a gateway between legacy pbxes.
>
> This represents just a subset of the available E1s in the world and 
> it's just a practical experience, but it's a fact for me. If I don't 
> have a card with echo cancellation, I don't offer reliability to my 
> customer; I've done that in the past and didn't work out.
>
> I'm not theoretically discussing anything, just sharing what I've been 
> through in the last 4 or 5 years.