SIP 199 Early Dialog Terminated vs 491 Request Pending
SIP 199 (Early Dialog Terminated) is a 1xx Provisional response, while 491 (Request Pending) is a 4xx Client Failure response. 199 indicates that a UAS can send this to indicate that an early dialog has been terminated. Used when forking results in multiple early dialogs. In contrast, 491 means that the request was received by a UAS that had a pending request within the same dialog. The UAS cannot process both requests simultaneously.
描述
A UAS can send this to indicate that an early dialog has been terminated. Used when forking results in multiple early dialogs.
何时出现
In forked call scenarios when one of the forked branches is cancelled because another branch was answered.
如何修复
No action needed. This is normal behavior in forked call setups. Ensure your UA handles early dialog termination gracefully.
描述
The request was received by a UAS that had a pending request within the same dialog. The UAS cannot process both requests simultaneously.
何时出现
When sending a re-INVITE while another re-INVITE is still being processed. Common during hold/unhold or codec change sequences.
如何修复
Wait for the pending transaction to complete before sending a new one. Implement proper glare handling (RFC 3261 Section 14.1).
主要区别
199 is a 1xx Provisional response, while 491 is a 4xx Client Failure response.
SIP 199: A UAS can send this to indicate that an early dialog has been terminated. Used when forking results in multiple early dialogs.
SIP 491: The request was received by a UAS that had a pending request within the same dialog. The UAS cannot process both requests simultaneously.
You encounter 199 when in forked call scenarios when one of the forked branches is cancelled because another branch was answered.
You encounter 491 when when sending a re-INVITE while another re-INVITE is still being processed. Common during hold/unhold or codec change sequences.
何时使用哪个
For 199 (Early Dialog Terminated): No action needed. This is normal behavior in forked call setups. Ensure your UA handles early dialog termination gracefully. For 491 (Request Pending): Wait for the pending transaction to complete before sending a new one. Implement proper glare handling (RFC 3261 Section 14.1).