SIP 183 Session Progress vs 603 Decline
SIP 183 (Session Progress) is a 1xx Provisional response, while 603 (Decline) is a 6xx Global 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, 603 means that the callee's machine was contacted successfully but the user explicitly does not wish to or cannot participate. Unlike 600, this may be because the callee doesn't want to communicate, not necessarily
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 callee's machine was contacted successfully but the user explicitly does not wish to or cannot participate. Unlike 600, this may be because the callee doesn't want to communicate, not necessarily because they're busy.
Quand vous le voyez
When the callee explicitly declines the call. This is an active rejection, not a busy or unavailable state.
Comment résoudre
The callee has declined. Respect their decision. Consider alternative communication methods (email, messaging).
Différences clés
183 is a 1xx Provisional response, while 603 is a 6xx Global 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 603: The callee's machine was contacted successfully but the user explicitly does not wish to or cannot participate. Unlike 600, this may be because the callee doesn't want to communicate, not necessarily
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 603 when when the callee explicitly declines the call. This is an active rejection, not a busy or unavailable state.
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 603 (Decline): The callee has declined. Respect their decision. Consider alternative communication methods (email, messaging).