My Freepbx (UK Based) configuration is as follows;
Sangoma Vega 60 FXO Gateway for my BT PSTN connection.
1 x SPA3102 FXS connection allowing an analogue phone to connect to my FreePBX
1 x SPA112 FXS connection allowing a second analogue phone to connect to my FreePBX.
All other phones are VOIP phones
Everything works fine except; if an incoming call is answered using either of the analogue phones for the first 3 or 4 seconds the user of the analogue phone hears an amount of echo. After this period of time the echo disappears and a everything is ok. I do not believe the caller hears any echo.
Any suggestions as to what is causing this would be gratefully accepted.
Echo in that location suggests that the FXO gateway is taking time to train, but that should affect the VoIP phones as well.
The primary echo cancellation on the SPAs will be to remove the echo from the attached phone so that the distant party doesn’t hear it. It’s not in the optimum position to cancel the echo from the other side because it is the wrong side of a non-trivial, and variable, delay. I’d also expect the VoIP phones to mainly or exclusively cancel echo from their analogue sides, although it is possible that they have very aggressive cancellation of the SIP side, as well.
If they do echo cancel the SIP side, they could make thinks worse, as they could learn the echo before the FXO has properly cancelled it and then subtract out echo that isn’t there, which will produce an echo.
Echo cancellers should converge quite well within about a second, but that does depend on there being outgoing speech during the whole convergence time. The time will be longer if both parties talk on top of each other.