We use a Quadro 2xi with Snom 360 handsets.

We have a remote user who has a simple BT router with a dynamic IP. Our office has a fixed IP.

His phone is set up to use <our public ip>:5060 as its both its Registrar and Outbound Proxy in the Snom 'Identity 1' settings.

Our router is set up to route anything incoming on UDP:5060 or TCP/UDP 6001 - 6099 to the Quadro.

The remote phone registers properly, and it can make outgoing calls to the PSTN successfully through the Quadro.

The problem is that when we make internal calls to (or receive internal calls from) the remote extension he can hear us but we cannot hear him. The extensions ring properly at either end when making internal calls.

I am sure this must be a NAT problem.