SIP 183 Session Progress vs 406 Not Acceptable
SIP 183 (Session Progress) is a 1xx Provisional response, while 406 (Not Acceptable) 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, 406 means that the resource identified by the request is only capable of generating responses with content characteristics not acceptable according to the Accept header.
Descripción
Used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP.
Cuándo lo verás
During call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
Cómo solucionarlo
No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA.
Descripción
The resource identified by the request is only capable of generating responses with content characteristics not acceptable according to the Accept header.
Cuándo lo verás
When content negotiation fails — the server cannot produce a response matching the Accept header fields in the request.
Cómo solucionarlo
Review the Accept headers in your request and broaden the acceptable content types.
Diferencias clave
183 is a 1xx Provisional response, while 406 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 406: The resource identified by the request is only capable of generating responses with content characteristics not acceptable according to the Accept header.
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 406 when when content negotiation fails — the server cannot produce a response matching the Accept header fields in the request.
Cuándo usar cada uno
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 406 (Not Acceptable): Review the Accept headers in your request and broaden the acceptable content types.