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T8 · T8-R03

One-way audio

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Learn it in 5 minutes

  • Signaling can be perfect while RTP fails in one direction.
  • Compare SDP connection addresses with the addresses that really send packets.
  • NAT and a firewall are the common reasons.
  • Codec mismatch usually fails the call, it does not half-succeed.
  • Hold and resume is a second offer. Check it too.
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Visual

One-way audio diagram
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What is going on

One-way audio means one side's packets arrive and the other's do not, or one side is playing silence because the direction attribute is inactive or sendonly. Look at RTP counters and the SDP, then the firewall, then QoS. QoS rarely drops only one direction unless the return path is a different route.

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Worked example

The agent hears the caller. The caller hears nothing. The caller's SDP says a private address the carrier cannot route. The fix is the media address CUBE advertises, not a new codec list.

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Quiz

1. A 200 OK with SDP proves two-way audio.

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Ecosystem

Sister pieces sit on the ecosystem page: the glossary, the mind map, the integration map, and the sibling labs.

  • SDP c= line — The address where media should be sent.
  • One-way audio — Media in a single direction.

Config. Note both c= addresses and whether the interface can reach them.

Troubleshooting. If both RTP streams are present and the user still hears silence, look at codec payload types and mute, not the firewall.

Bridge. SRTP without matching keys sounds like silence or a dropped call. Check whether both legs intended SRTP.

Mind map, sister technologies, and future hooks live on the ecosystem page.

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Sources

Product screens move. Confirm the guide for your release before you change a live system.

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Sources and go deeper

Opened 2026-10. A row marked confirm has no link, because that page was not verified.

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