[Freeswitch-users] Removing echo.

[Steve Underwood]

On 03/19/2013 09:10 PM, Sean Devoy wrote:
>
> -----Original Message-----
> From: freeswitch-users-bounces at lists.freeswitch.org 
> [mailto:freeswitch-users-bounces at lists.freeswitch.org] On Behalf Of 
> Steve Underwood
> Sent: Tuesday, March 19, 2013 3:32 AM
> To: FreeSWITCH Users Help
> Subject: Re: [Freeswitch-users] Removing echo.
>
> If you want to understand why a call from a cell phone to an FS 
> server, leaving a voice mail, might result in you hearing echo, you'll 
> have to describe the path between you and the FS server.
>
> Cell Phone => Cell Carrier => ?? => Internet => Voip Provider => LAN => FS
>
>
FS is definitely not the source of the echo in this path. When sending 
voice mail to FS is has distinct receive and transmit paths, with no 
possibility of crosstalk. The only way FS could introduce echo is if the 
call comes in through an analogue PSTN connexion. You don't have those, 
so FS is not to blame.

The LAN surely isn't to blame.

You indicated the VoIP provider has an internet path coming in. If that 
is true they probably can't be the source of the echo, as they will just 
pass the signals through.

?? looks like the probable rogue here. Presumably the cell carrier 
interfaces to the PSTN, and ?? is some VoIP provider interfacing between 
the PSTN and the IP world. A large VoIP provider would interface to the 
PSTN with a digital connection, and echo would not occur. However, don't 
rule out the possibility of some small outfit using analogue lines.

There is a slight possibility of the cell carrier being at fault, 
although it is unlikely. In the early days of GSM it was quite common 
for a call that didn't connect properly to result in a huge echo to the 
user. This was because of bugs in the way the base station's echo 
canceller was handled. Over the years the bugs causing this have mostly 
been resolved, but you still get massive echo occasionally. It is not 
unknown for a particular call path to keep fooling the echo canceller 
during its adaption phase, so almost every call over the same path 
results in echo.

The cell phone has an echo canceller to prevent earpiece to mic leakage 
from sending an echo back to the line, but this will not affect the user 
of the phone. The phone itself should not be the cause of your problem.


So...... its looking like ?? is the probable problem area. I assume the 
use of ?? means you have no idea what is there. Can you try an alternate 
way to get from your cell phone to the FS box. Perhaps using a different 
VoIP provider who can be assumed to provide a genuinely different path?

Steve