I'm building an OpenVPN Server to connect from the Internet into my Home-LAN and make phone calls using SIP.
I've got an AVM Fritzbox Home-Router from my ISP which has a build in SIP-Server for Softphones.
I use Softphone Software like Linphone and Jitsi.
In my LAN SIP Calls work fine with no problems.
But: when I connect from outside to the OpenVPN Server and trying to make calls I got issues.
- The connection to the VPN could be established.
- My Softphone can actually login to the SIP-Server of my fritzbox.
- So I try to make a call and it works.
- The other side received my call and when I answer it the call is established (means SIP-protocol might work fine).
- But!: the call has NO SOUND AT ALL on both sides (I suggest that might be a RTP problem ).
Has someone any idea what can cause that rtp doesn't work?
Could it be a routing issue? Or a port issue?