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.