[Asterisk-Users] Why echo occurs

[Bruce Ferrell]

Eric, youmight want to search the archives.  I wrote a rather lengthy 
explaination on echo and echo control last year.

Eric Bishop wrote:
> Hi all,
> 
> Can someone give me a simple rational explanation why a $5 analog
> handset  gives me no echo whatsoever on an analog PSTN line, but
> PSTN-VoIP devices such as the TDM400 and Sipuras do and thus require
> software-based echo cancellation. Surely a $5 analog handset does not
> have an "echo canceller".
> 
> The echo I mean is when I hear myself while talking to another party.
> 
> I have heard it said it is because of some slowdown of the signal. But
> where is this mysterious bottleneck?
> 
> 1. It is not in the Asterisk box because IP to IP calls do not suffer
> this malady
> 
> 2. It is not from the Central Office to my premesis because my $5
> analogue handset works without echo. Also PRI ISDN works without echo.
> 
> Can anyone explain what I am missing?
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