SIP 181 Call Is Being Forwarded vs 491 Request Pending
SIP 181 (Call Is Being Forwarded) is a 1xx Provisional response, while 491 (Request Pending) is a 4xx Client Failure response. 181 indicates that a proxy server may send this to indicate that the call is being forwarded to a different set of destinations. 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.
Описание
A proxy server may send this to indicate that the call is being forwarded to a different set of destinations.
Когда вы это видите
When the callee has call forwarding enabled and the request is being redirected to another number or device.
Как исправить
No action needed. The call is being redirected. If forwarding is unintended, the callee should update their forwarding settings.
Описание
The request was received by a UAS that had a pending request within the same dialog. The UAS cannot process both requests simultaneously.
Когда вы это видите
When sending a re-INVITE while another re-INVITE is still being processed. Common during hold/unhold or codec change sequences.
Как исправить
Wait for the pending transaction to complete before sending a new one. Implement proper glare handling (RFC 3261 Section 14.1).
Ключевые различия
181 is a 1xx Provisional response, while 491 is a 4xx Client Failure response.
SIP 181: A proxy server may send this to indicate that the call is being forwarded to a different set of destinations.
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 181 when when the callee has call forwarding enabled and the request is being redirected to another number or device.
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.
Когда что использовать
For 181 (Call Is Being Forwarded): No action needed. The call is being redirected. If forwarding is unintended, the callee should update their forwarding settings. 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).