Service Error Codes
When using any communications device, it’s quite possible that you will end up reaching some disconnected numbers. It’s also possible that you’ll reach busy phone lines, and other inconvenient situations. All of these phone call scenarios have corresponding error codes to let you, the caller, know exactly what happened.
The following is a list of the most common error codes to be encountered when using any internet-based communications device. For a more comprehensive list, take a look at this HTTP Status Code List or this SIP Response Code List.
SIP Response Codes:
400 Bad Request: The request could not be understood due to malformed syntax.
403 Forbidden: The request submitted is understood, but will not be fulfilled. This can be due to an incorrect password, insufficient funds in your VOIP account, and many other reasons. It’s necessary to contact your service provider to know why exactly the request was denied.
404 Not Found: The number specified could not be found at the domain given in the request. This means either the phone number doesn’t exist, or it can’t be reached using the service you are using.
408 Request Timeout: The user specified could not be found within a reasonable amount of time. The request may be submitted unchanged at a future time.
480 Temporarily Unavailable: The user specified is currently temporarily not available. This means the recipient was located, but is in a state that precludes communication between the caller and callee.
486 Busy Here: The user specified is currently busy, meaning they don’t have an available phone line.
504 Server Timeout: The server did not receive a timely response from the server it made a request to.
603 Decline: The callee’s machine was successfully contacted but the request was denied because they do not or cannot participate in the request.