I hear an echo in SIP calls

Hi, we have 10 SIP phones (Linksys SPA942) working perfectly and we have an TDM400P 3 FXO interfaces.
Sometimes, when i dial a SIP station (in office) running in my own LAN i can hear an echo…
The Rx and TX on each phone at office is in default mode, i don’t changed anything.
Please how can i fix that?


The echo will be in the handset, so you need to make sure that users don’t have the volume to high.