SIP 301 Moved Permanently vs 481 Call/Transaction Does Not Exist
SIP 301 (Moved Permanently) is a 3xx Redirection response, while 481 (Call/Transaction Does Not Exist) is a 4xx Client Failure response. 301 indicates 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. In contrast, 481 means that the UAS received a request that does not match any existing dialog or transaction. The call state may have been lost.
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.
Description
The UAS received a request that does not match any existing dialog or transaction. The call state may have been lost.
When You See It
When sending a BYE, re-INVITE, or UPDATE for a call that the server has no record of. Common after server restarts.
How to Fix
The dialog has been lost. Terminate the local call state. For re-INVITE failures, re-establish the call from scratch.
Key Differences
301 is a 3xx Redirection response, while 481 is a 4xx Client Failure response.
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.
SIP 481: The UAS received a request that does not match any existing dialog or transaction. The call state may have been lost.
You encounter 301 when when a user has permanently changed their SIP address. All future calls should be directed to the new URI.
You encounter 481 when when sending a BYE, re-INVITE, or UPDATE for a call that the server has no record of. Common after server restarts.
When to Use Which
For 301 (Moved Permanently): Update your address book or routing tables to use the new Contact URI provided in the response. For 481 (Call/Transaction Does Not Exist): The dialog has been lost. Terminate the local call state. For re-INVITE failures, re-establish the call from scratch.