Intermittent one-way audio (RTP not received) with Telnyx → Retell

Support Help
1

Hi team,

We are experiencing a critical intermittent one-way audio issue with our Retell + Telnyx setup and need engineering assistance.

:wrench: Setup:

  • Telnyx Elastic SIP trunk → Retell (no self-hosted infrastructure)
  • We are NOT running our own VPS, LiveKit instance, or firewall
  • No custom NAT or network configuration on our side

:telephone_receiver: Issue description:

  • Calls connect successfully (SIP signaling is correct: INVITE → 200 OK → ACK)
  • In some calls, everything works perfectly (audio both ways)
  • In other calls:
  • The callee cannot hear anything
  • We also do not receive any inbound audio
  • The issue is intermittent but happening more frequently over time

:bar_chart: Key observations:

  • Telnyx has analyzed the calls and confirmed:
  • RTP from Retell → Telnyx is working correctly
  • RTP from Telnyx → Retell is being sent, but not received
  • MOS score is high (~4.4+), confirming outbound audio is fine
  • Retell recordings contain the AI voice → audio is being generated correctly
  • This strongly indicates a one-way audio issue on the inbound RTP path

:red_exclamation_mark:Important:

  • Since some calls work and others don’t, this does NOT look like a configuration issue on our side
  • If it were firewall/NAT/config related, all calls would fail consistently
  • The intermittent nature suggests a media routing issue between Telnyx and Retell (possibly specific nodes, regions, or RTP handling)

:round_pushpin: What we need:

  • Please check inbound RTP handling on your side (Telnyx → Retell / LiveKit)
  • Verify if there are any issues with media routing, specific nodes, or regions
  • Confirm whether Retell is consistently receiving RTP streams from Telnyx
  • Check if there are any known issues affecting Telnyx integrations

:police_car_light: This is blocking production, so we need this escalated to engineering.

We can provide:

  • Multiple failing call IDs
  • Working call IDs for comparison
  • Telnyx analysis reports
  • PCAP files if needed

Please let us know what additional data you need.

Thanks.

2

Hey @ceseminst.eia01

Could you please share your Call IDs were you faced that issue? This will help us investigate the issue more effectively.

Thank you!

3

Sure:

To same number:
call_bb0f33bf2fcbcfb709e8422eec2
call_6ccf187ffb0f64a107f06efdee2

To different number:
call_8bdfe0080f22d8ba9e7ee8b94a1
call_fe554d119b3581778a32e3108ad
call_a32e2d4a21cfb7359fbb2b5c018

4

Hey @ceseminst.eia01

Thanks for sharing the call ID. I’ve forwarded them to our team for further investigation.

We’ll get back to you as soon as we have an update.

Best regards

5

Hey @ceseminst.eia01

Hello, we looked into the calls and it looks like we are not receiving the RTP packets from Telnyx(see screenshot). Can you please share the Telnyx pcap with RTP for the examples?

Thank You

image
image3336×806 140 KB

6

Hey,

Pcap for call_bb0f33bf2fcbcfb709e8422eec2 → DvreFhFzW61IroXIIMsqcDSIaXS.pcap
Pcap for call_6ccf187ffb0f64a107f06efdee2 → tn3TIM6SIpM5rjeIpPN7uF1TEMV.pcap

Pcap for call_a32e2d4a21cfb7359fbb2b5c018 → Itmbbd2HbWi0dff0ayb24Bvwmka.pcap
Pcap for call_fe554d119b3581778a32e3108ad → w6y7yvwZNt5y15pd4Nmxtv8YLqH.pcap
Pcap for call_8bdfe0080f22d8ba9e7ee8b94a1 → Itmbbd2HbWi0dff0ayb24Bvwmka.pcap

Thanks

(Attachment DvreFhFzW61IroXIIMsqcDSIaXS.pcap is missing)

(Attachment tn3TIM6SIpM5rjeIpPN7uF1TEMV.pcap is missing)

(Attachment Itmbbd2HbWi0dff0ayb24Bvwmka.pcap is missing)

(Attachment w6y7yvwZNt5y15pd4Nmxtv8YLqH.pcap is missing)

(Attachment Itmbbd2HbWi0dff0ayb24Bvwmka.pcap is missing)

7

How can I share .pcap with you?

8

Hey @ceseminst.eia01

You can share that on email at support@retellai.com and share your email from which you sent

Thank You

9

Sent, my email: ceseminst.eia01@gmail.com

10

Did you sent Telnyx pcap with RTP for the examples?

11

I sent .pcap from all calls mentioned. Do you need somethin more?

12

Okay, I’ve notified our team to look into this.

13

Ok thanks, let me know if you have something