SIP 183 Session Progress vs 488 Not Acceptable Here
SIP 183 (Session Progress) is a 1xx Provisional response, while 488 (Not Acceptable Here) is a 4xx Client Failure response. 183 indicates that used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP. In contrast, 488 means that the request was understood but the session description (SDP) is not acceptable. The response may contain a list of acceptable media parameters.
Description
Used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP.
When You See It
During call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
How to Fix
No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA.
Description
The request was understood but the session description (SDP) is not acceptable. The response may contain a list of acceptable media parameters.
When You See It
When codec negotiation fails — the callee cannot handle any of the codecs offered in the SDP. Common in interop scenarios.
How to Fix
Check the Warning header or SDP in the response for acceptable parameters. Add compatible codecs (e.g., G.711 as a fallback) to your offer.
Key Differences
183 is a 1xx Provisional response, while 488 is a 4xx Client Failure response.
SIP 183: Used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP.
SIP 488: The request was understood but the session description (SDP) is not acceptable. The response may contain a list of acceptable media parameters.
You encounter 183 when during call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
You encounter 488 when when codec negotiation fails — the callee cannot handle any of the codecs offered in the SDP. Common in interop scenarios.
When to Use Which
For 183 (Session Progress): No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA. For 488 (Not Acceptable Here): Check the Warning header or SDP in the response for acceptable parameters. Add compatible codecs (e.g., G.711 as a fallback) to your offer.