[Asterisk-Users] Echo on internal SIP

[Jeff Heath]

The echo is almost certainly acoustic echo from the phones at the other
side of the conversation ("other side" being the side opposite where the
echo is heard).

Acoustic echo in phones comes from coupling within the phone (i.e. sound
waves being transmitted inside the phone case or through the body of the
phone - this is a problem in cell phones).  The other place it comes
from is sound waves bouncing off the walls inside a room (speaker phones
only).  Good quality phones are engineered to reduce the acoustic
coupling inside the phone and have acoustic echo cancelers that cancel
any echo that does occur.

Turning down the volume on the phones is a good first step. 
Unfortunately, I don't know enough about Asterisk echo cancellation to
render any useful advice about Asterisk settings, but I do know this
much...  Most (almost all) echo cancelers in telephone network equipment
are designed to cancel the electrical echo that is created by a hybrid
that converts signals from 4 wire to 2 wire.  Canceling acoustic echo is
more difficult than canceling electrical echo.  Many times an echo
canceler that works on electrical echo won't work nearly as well on
acoustic echo.

Hopefully, someone who knows more about Asterisk's echo cancellation
capabities will post a follow up about whether or not there are settings
in Asterisk that might help.

Jeff Heath



On Thu, 2005-03-31 at 10:36, Philip Siegrist wrote:
> Hi All,
> 
> On my * server I am getting echo on internal SIP calls. I.E. Sip 2
> Sip. Calls going over the T1 via the T100p are fine.
> 
> I have used ulaw and gsm, gsm has less echo but it is still noticable.
> All phones are snom 190s.  Any ideas on what i can do to cancel this.
> 
> Thanks,
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