we run a VoIP system and have amongst others a Sipura SPA-921. When we use the SPA-921 within our office all is fine. Now we took it to a home office and made the link via VPN. Still the communication between office and home office is fine.
But when trying to transfer a call, only the first 'leg' works. So external A calls B (SPA-921 over VPN) and B wants to transfer to C (via VPN). B can put A on hold and talk to C but even after pressing the XFER button and hanging up A is not connected to C.
Is there anything to set for the SPA-921 so that call transfers work via VPN as well?