Echoes with T32G phones

[mrecob]

Since installing our new phone switch and yealink phones in January we have been having intermittent echo issues. I would place a call to someone inside the building. They would answer me on speaker. They would report hearing a very annoying echo. When they go off speaker, the echo goes away and when they go back on speaker the echo does not return. The next call can be free of echoes. We have also had a report of outside and inside callers using one of our conference lines but the echoes were so bad, we had to end the conference call and use an alternative conference call solution. I first contacted Barracuda Networks. They had me remove all but their G.711 codecs from the phone switch configuration. Echoes persist and they are stumped. Echo cancellation is enabled in all phones. Do you have any idea what we can do?

Yealink T32G FW:32.70.0.132
Cudatel Communications Server 470 FW:3.0.002.026