# Inbound one-way audio — SDP codec answer diverges by backend stack (BYOC, +902168882917)

**URL:** <https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600>\
**Category:** Support Help\
**Tags:** telephony\
**Created:** [September 4, 2026, 4:11pm UTC](https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600 "2026-09-04T16:11:53Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Maytras](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/maytras/32/2667_2.png) [@Maytras](https://community.retellai.com/u/Maytras)\
**Post date:** [September 4, 2026, 4:11pm UTC](https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600/1 "2026-09-04T16:11:53Z")

</div>

Production-critical, ongoing since Sept 3→4 night. Already opened ticket [#58155](https://github.com/Mayka-Global-TradeTech/TradeTech/issues/58155) (auto-ack only so far).

Symptom: caller hears complete silence on all inbound calls, agent hears/transcribes caller fine. Outbound unaffected.

Root cause from pcap\_url on 10 calls: carrier SIP offer identical every time (`RTP/AVP 8 0 18 101`). When call enters via signaling IP `18.98.16.121`, Retell answers with a single codec (`RTP/AVP 0 101`) — audio works. Since Sept 4, calls enter via `.120`/`.123` and Retell answers with four codecs (`RTP/AVP 0 8 9 101`) — ambiguous negotiation, caller’s carrier drops mismatched RTP.

Working call: `call_103196a07051d1993c37df131d6` (2026-09-03T18:22Z)  
Broken call: `call_c411843e8d47185b507cf6a6178` (2026-09-04T15:27Z)  
Agent: `agent_0b26275640e8519a44b12446b6`

@Shah-Fazal — since you’re already looking at SIP traces on the 18.98.16.x pool today (Sone’s thread), could this be related? Appreciate any help, our customers can’t reach us by phone.

---

<div class="post-metadata">

**Author:** ![Shah-Fazal](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/shah-fazal/32/2522_2.png) [@Shah-Fazal](https://community.retellai.com/u/Shah-Fazal)\
**Post date:** [September 4, 2026, 4:22pm UTC](https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600/2 "2026-09-04T16:22:27Z")

</div>

Hello @Maytras I’m checking this with the team and will get back to you as soon as I have an update.

Thank You

---

<div class="post-metadata">

**Author:** ![Shah-Fazal](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/shah-fazal/32/2522_2.png) [@Shah-Fazal](https://community.retellai.com/u/Shah-Fazal)\
**Post date:** [September 4, 2026, 5:08pm UTC](https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600/3 "2026-09-04T17:08:02Z")

</div>

Hello @Maytras We have pushed a fix, please let me know if everything is working as expected.

Thank You

---

<div class="post-metadata">

**Author:** ![Maytras](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/maytras/32/2667_2.png) [@Maytras](https://community.retellai.com/u/Maytras)\
**Post date:** [September 4, 2026, 8:23pm UTC](https://community.retellai.com/t/inbound-one-way-audio-sdp-codec-answer-diverges-by-backend-stack-byoc-902168882917/3600/4 "2026-09-04T20:23:33Z")

</div>

Hi @Shah-Fazal,

Confirmed — the fix is working. Just tested an inbound call and audio came through both ways. Thank you for the quick turnaround on this.