SIP 181 Call Is Being Forwarded vs 301 Moved Permanently
SIP 181 (Call Is Being Forwarded) is a 1xx Provisional response, while 301 (Moved Permanently) is a 3xx Redirection 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, 301 means that the user can no longer be found at the address in the Request-URI. The client should direct future requests to the new address in the Contact header.
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 user can no longer be found at the address in the Request-URI. The client should direct future requests to the new address in the Contact header.
When You See It
When a user has permanently changed their SIP address. All future calls should be directed to the new URI.
How to Fix
Update your address book or routing tables to use the new Contact URI provided in the response.
Key Differences
181 is a 1xx Provisional response, while 301 is a 3xx Redirection response.
SIP 181: A proxy server may send this to indicate that the call is being forwarded to a different set of destinations.
SIP 301: The user can no longer be found at the address in the Request-URI. The client should direct future requests to the new address in the Contact header.
You encounter 181 when when the callee has call forwarding enabled and the request is being redirected to another number or device.
You encounter 301 when when a user has permanently changed their SIP address. All future calls should be directed to the new URI.
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 301 (Moved Permanently): Update your address book or routing tables to use the new Contact URI provided in the response.