Find the codec negotiated on a failed or poor-quality call

A quiet or distorted call is not enough evidence to blame the codec. The negotiated codec, packet interval and network measurements must be checked on the same call.

Collect the offer and answer

Preserve the SDP from the INVITE and final answer, including payload mappings and packet-time attributes. Record whether an SBC or PBX transcoded between legs. A codec listed in an offer was not necessarily selected.

Inspect the media

Compare RTP sequence gaps, jitter and packet timing in both directions. If signalling succeeds but audio fails, check the negotiated media addresses and firewall path before changing codec order. If only one codec fails, repeat the test with a known supported option on the same route and document both results.

Use consistent time zones and redact customer numbers without losing call identifiers needed for provider escalation.

The voice codecs reference helps interpret codec and packetisation differences.