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One-way audio

A 200 OK can be perfect while one RTP direction is missing. Read direction, c=, and who is actually sending.

Learn in 5 minutes

  1. Separate a completed offer/answer from flowing RTP
  2. Check sendonly, recvonly, and inactive before blaming the codec
  3. Use RTCP to see which side is silent

Visual

Answer says sendonly · study drawing · cyphermonkeylabs.com AliceCarrier INVITE 100 200 ACK

SVG HTML PNG

Signaling success is the first box, not the last.

Worked example

Spot sendonly in the answer Extract the INVITE and the 200 OK. Compare a=sendrecv in the offer with the answer direction.

  1. Press Extract SIP.
  2. Read the offer direction.
  3. Read the answer direction.

Fault

The callee hears the caller. The caller hears nothing. SIP is 200 OK.

recvonly is the answerer's direction. They receive and they do not send, which matches a sender report from only 203.0.113.10.

Quiz

One-way audio with a 200 OK means


An answer of a=sendonly means the answerer will


a=inactive means


If direction is sendrecv on both sides, you next check


A sender report from only one side shows


The Wireshark references in this lesson are for


Ecosystem

Glossary, sister systems, and the integration seam for this room.

Workforce management WFM forecasts volume and builds schedules. It consumes contact-center events. It does not parse Via headers. When a forecast is wrong, the SIP symptom is usually queue delay and 480 or carrier congestion, not a broken dialog ID.

Programmable communications APIs Twilio’s docs home is API reference, tutorials, and integration for Twilio products. Elastic SIP Trunking is the SIP-shaped product already cited in this lab. This page does not define the word CPaaS from an RFC. Read the vendor page before you copy a diagram that uses that word.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper