SIP 183 Session Progress vs 600 Busy Everywhere
SIP 183 (Session Progress) is a 1xx Provisional response, while 600 (Busy Everywhere) 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, 600 means that the callee's end system was contacted successfully but the callee is busy and does not wish to take the call at this time. Unlike 486 (Busy Here), this is a definitive response.
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 callee's end system was contacted successfully but the callee is busy and does not wish to take the call at this time. Unlike 486 (Busy Here), this is a definitive response.
When You See It
When the callee has rejected the call on all devices. No other endpoints should be tried. The user is universally busy.
How to Fix
Wait and try again later. No alternative contact points exist. The callee must become available on their own.
Key Differences
183 is a 1xx Provisional response, while 600 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 600: The callee's end system was contacted successfully but the callee is busy and does not wish to take the call at this time. Unlike 486 (Busy Here), this is a definitive response.
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 600 when when the callee has rejected the call on all devices. No other endpoints should be tried. The user is universally busy.
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 600 (Busy Everywhere): Wait and try again later. No alternative contact points exist. The callee must become available on their own.