Callers hear each other only one way: classic one-way audio.
Signalling runs over SIP, audio over RTP. RTP arrives on a different port than SIP, and NAT or firewall blocks one direction.
support/telefonie-voip/one-way-audio-nat-rtpsteps: 4
Try this first
- Open the RTP port range on the firewall toward PBX or phone
- Check NAT type on the router, no symmetric NAT
- Enable STUN or an SBC on the PBX side
- Inspect codec and SDP negotiation in pcap
When to bring us in
Symmetric NAT at a CGNAT provider: ask for a public IP or a full SBC solution, otherwise it stays flaky.
See also
- Voys, BelXS or RoutIT, which cloud PBX fits?Three popular NL platforms, differences are admin UI, partner model and per-user price.
- Teams Phone: Calling Plan, Direct Routing or Operator Connect?Three ways to connect PSTN to Teams, cost and management differ a lot.
- 3CX: self-host on VPS or take 3CX cloud?Self-host saves licence, but you own SBC, backup and updates.
None of the above fits?
Describe your situation below. We pass your input plus the steps you already saw to our AI and return tailored next-step advice. If it's too risky to DIY, we'll say so.
Or skip the DIY entirely
Our Managed IT clients do not look these things up. One point of contact, a fixed monthly price, resolved within working hours.