Locate the response family
- 1xx ProvisionalRequest is progressing183 belongs here
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request
- 5xx Server failureServer could not fulfil
- 6xx Global failureFailure across destinations
Read the status with its request method and call leg. For example, 200 after REGISTER confirms a binding; it does not prove an INVITE succeeded.
What this response means
The receiver provides provisional session-progress information. It can participate in early-media handling, but 183 alone does not guarantee that usable audio is present.
Read it in context
A carrier may use early media for announcements or progress tones before answer. SDP and the surrounding reliable-provisional or offer/answer behavior determine how media is negotiated in the actual exchange.
Administrator checks
Check whether the response carries a relevant session description, whether the expected media arrives and whether an intermediary suppresses or changes it. Compare both call legs if the PBX relays the announcement.
Next action and common mistake
Do not convert every 183 into a failure or assume it means the call was answered for billing. Use carrier records for billing questions and final signaling plus media observations for technical acceptance.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.