Hi QCMP,
Usually people with one-way audio problems are directed to look at the NAT in their router. While there could certainly be other forces in play here, you could check your router. If you provide us with the model of router you have, that may also help.
Disabling SIP ALG if present in your router usually helps, and temporarily placing your OBi inside your router's DMZ is another idea to help isolate the cause of the problem.
I would imagine you have already checked this, but make sure you are running the latest/current firmware for your OBI110. You can check your current firmware at Status -> System Status. The
current firmware release for the OBI110 appears to be 1.3.0 (Build: 2711).
Let us know,

pc44