SIP 181 Call Is Being Forwarded vs 204 No Notification
SIP 181 (Call Is Being Forwarded) is a 1xx Provisional response, while 204 (No Notification) is a 2xx Success 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, 204 means that the request was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request.
Description
A proxy server may send this to indicate that the call is being forwarded to a different set of destinations.
When You See It
When the callee has call forwarding enabled and the request is being redirected to another number or device.
How to Fix
No action needed. The call is being redirected. If forwarding is unintended, the callee should update their forwarding settings.
Description
The request was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request.
When You See It
When subscribing to event packages that may not generate immediate notifications, such as dialog or presence packages.
How to Fix
No fix needed. The subscription was accepted but there is no state change to notify about yet.
Key Differences
181 is a 1xx Provisional response, while 204 is a 2xx Success response.
SIP 181: A proxy server may send this to indicate that the call is being forwarded to a different set of destinations.
SIP 204: The request was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request.
You encounter 181 when when the callee has call forwarding enabled and the request is being redirected to another number or device.
You encounter 204 when when subscribing to event packages that may not generate immediate notifications, such as dialog or presence packages.
When to Use Which
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 204 (No Notification): No fix needed. The subscription was accepted but there is no state change to notify about yet.