SIP 181 Call Is Being Forwarded vs 480 Temporarily Unavailable
SIP 181 (Call Is Being Forwarded) is a 1xx Provisional response, while 480 (Temporarily Unavailable) 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, 480 means that the callee's end system was contacted successfully but the callee is currently unavailable. The client may retry after some time.
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 callee's end system was contacted successfully but the callee is currently unavailable. The client may retry after some time.
When You See It
When the user exists but is not currently reachable — phone is off, DND mode enabled, or all lines are busy.
How to Fix
Try calling again later. Check if the callee has DND enabled or if their device is powered off. Configure voicemail for unavailable scenarios.
Key Differences
181 is a 1xx Provisional response, while 480 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 480: The callee's end system was contacted successfully but the callee is currently unavailable. The client may retry after some time.
You encounter 181 when when the callee has call forwarding enabled and the request is being redirected to another number or device.
You encounter 480 when when the user exists but is not currently reachable — phone is off, DND mode enabled, or all lines are busy.
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 480 (Temporarily Unavailable): Try calling again later. Check if the callee has DND enabled or if their device is powered off. Configure voicemail for unavailable scenarios.