[Freeswitch-users] Removing echo.

[Klaus Hochlehnert]

Hi,

I would also vote for some EC tuning possibility in FS, even if it's not the "right place".

I have an installation which uses an ISDN/SIP-Gateway (with its own EC).
> Telco - ISDN - ISDN-/SIP-Gateway - FS - Phone
Sometimes they hear an echo which I can record to a sound file with the FS record command.
The echo is unfortunately not reliably reproducible, not even to the same destination number.

After some discussions with the vendor of the gateway they asked me to connect a phone directly to their gateway.
And from that phone we never heard an echo (which is strange, I know).

Currently I don't have any clue what the source of the echo is, but if FS could be tuned in that way I might get rid of it.

Thanks
Klaus


-----Ursprüngliche Nachricht-----
Von: freeswitch-users-bounces at lists.freeswitch.org [mailto:freeswitch-users-bounces at lists.freeswitch.org] Im Auftrag von Steve Underwood
Gesendet: Mittwoch, 20. März 2013 03:14
An: FreeSWITCH Users Help
Betreff: Re: [Freeswitch-users] Removing echo.

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



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