SIP - 6xx: Global Failure Responses

This response class indicates that the server knows that the request will fail wherever it is tried. As a result, the request should not be sent to other locations.

Only a server having definitive knowledge of the user identified by the Request-URI in every possible instance should send a global error class response. Otherwise, a client error class response should be sent.

A Retry-After header field can be used to indicate when the request might be successful. Some of the important responses are discussed below −

600 Busy Everywhere

• This response indicates that the call to the specified Request-URI could be answered in other locations.

603 Decline

• This response could indicate the called party is busy, or simply does not want to accept the call.

604 Does Not Exist Anywhere

• This response is similar to the 404 Not Found response but indicates that the user in the Request-URI cannot be found anywhere.

• This response should only be sent by a server having access to all the information about the user.

606 Not Acceptable

• This response indicates that some aspect of the desired session is not acceptable to the UAS, and as a result, the session cannot be established.

• The response may contain a Warning header field with a numerical code describing exactly what was not acceptable.

• The request can be retried with different media session information.