SIP 183 Session Progress vs 400 Bad Request
SIP 183 (Session Progress) is a 1xx Provisional response, while 400 (Bad Request) 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, 400 means that the request could not be understood due to malformed syntax. The client should not repeat the request without modifications.
Mô tả
Used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP.
Khi bạn thấy mã này
During call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
Cách khắc phục
No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA.
Mô tả
The request could not be understood due to malformed syntax. The client should not repeat the request without modifications.
Khi bạn thấy mã này
When the SIP message has syntax errors, missing required headers, or invalid header values.
Cách khắc phục
Review the SIP message for syntax errors. Check required headers (To, From, Call-ID, CSeq, Via, Max-Forwards) and ensure proper formatting.
Sự khác biệt chính
183 is a 1xx Provisional response, while 400 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 400: The request could not be understood due to malformed syntax. The client should not repeat the request without modifications.
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 400 when when the SIP message has syntax errors, missing required headers, or invalid header values.
Khi nào dùng cái nào
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 400 (Bad Request): Review the SIP message for syntax errors. Check required headers (To, From, Call-ID, CSeq, Via, Max-Forwards) and ensure proper formatting.