SIP 183 Session Progress vs 416 Unsupported URI Scheme
SIP 183 (Session Progress) is a 1xx Provisional response, while 416 (Unsupported URI Scheme) 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, 416 means that the server cannot process the request because the URI scheme in the Request-URI is unknown to the server.
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.
Quand vous le voyez
During call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
Comment résoudre
No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA.
Description
The server cannot process the request because the URI scheme in the Request-URI is unknown to the server.
Quand vous le voyez
When using a URI scheme (e.g., tel:, im:, pres:) that the receiving server does not support.
Comment résoudre
Use a supported URI scheme. Most SIP servers support sip: and sips: schemes. Check server capabilities with OPTIONS.
Différences clés
183 is a 1xx Provisional response, while 416 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 416: The server cannot process the request because the URI scheme in the Request-URI is unknown to the server.
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 416 when when using a URI scheme (e.g., tel:, im:, pres:) that the receiving server does not support.
Quand utiliser lequel
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 416 (Unsupported URI Scheme): Use a supported URI scheme. Most SIP servers support sip: and sips: schemes. Check server capabilities with OPTIONS.