SIP 183 Session Progress vs 439 First Hop Lacks Outbound Support
SIP 183 (Session Progress) is a 1xx Provisional response, while 439 (First Hop Lacks Outbound Support) 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, 439 means that the first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
描述
Used to convey information about the progress of the call that is not otherwise classified. Often carries early media (ringback tones, announcements) via SDP.
何时出现
During call setup, especially in PSTN interworking scenarios. The response may contain SDP for early media like custom ringback tones or IVR prompts.
如何修复
No fix needed — this is informational. If early media is not playing, check codec negotiation and SDP handling in your UA.
描述
The first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
何时出现
When a UA configured for SIP outbound connects to a proxy that doesn't support the outbound option-tag.
如何修复
Upgrade the outbound proxy to support RFC 5626, or configure the UA to not require outbound support.
主要区别
183 is a 1xx Provisional response, while 439 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 439: The first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
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 439 when when a UA configured for SIP outbound connects to a proxy that doesn't support the outbound option-tag.
何时使用哪个
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 439 (First Hop Lacks Outbound Support): Upgrade the outbound proxy to support RFC 5626, or configure the UA to not require outbound support.