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voip guide

Troubleshooting One-Way Audio

One-way audio usually means signaling completed, but RTP media only works in one direction. The fastest path is to identify which direction is missing audio, then compare SIP SDP with the RTP packets.

Start With Direction

  • Confirm who cannot hear whom.
  • Check whether RTP exists from each endpoint.
  • Compare packet counts and SSRCs for both directions.
  • Do not assume SIP success means media is healthy.

Common Causes

  • Private IP addresses advertised in SDP.
  • Firewall rules allowing signaling but blocking RTP ports.
  • NAT pinholes opening in only one direction.
  • SBC or PBX media anchoring disabled or misrouted.
  • Codec negotiation succeeds but media is sent to the wrong address.

Best Evidence

A packet capture near the PBX or SBC is usually the best proof. It can show whether RTP was received, where it was sent, and whether the advertised SDP address matches the actual media path.