The Retell Community is where innovators, call center leaders, and AI enthusiasts come together to share ideas, learn best practices, and explore the future of voice automation. Join to connect with peers, get early access to product updates, and collaborate on building human-like AI voice experiences that transform customer service.

Retell AI

Hey everyone,

I’m dealing with an urgent SIP/RTP issue between Telnyx and Retell and could really use some help from someone experienced in VoIP.

Setup:
Telnyx SIP trunk → Retell (LiveKit infra)

Problem:
Intermittent one-way audio on outbound calls:

* SIP signaling is always fine (INVITE → 183 → 200 OK)
* In failing calls, the callee cannot hear anything
* Retell also doesn’t seem to receive RTP from Telnyx

What I’ve already checked:

* Disabled RTP Auto Adjust
* Disabled “Accept any RTP packets”
* Tested Proxy vs Default media handling
* SDP looks correct (IP/port + codec properly negotiated)
* Issue still happens randomly

Telnyx has reviewed PCAPs but hasn’t provided a fix yet.

At this point it looks like either:

* RTP is not being sent to the correct IP/port consistently
* Or there’s some edge/routing issue with Retell media endpoints

If anyone has dealt with similar Telnyx ↔ Retell (or SIP ↔ WebRTC bridge) issues, I’d really appreciate some guidance.

Happy to share PCAPs  if needed.


Thanks 🙏