What do telephony & error codes mean?

Overview of common SIP telephony and error codes and their meanings in sipgate VoIP systems.

These are the most common error codes

401 Invalid credentials	The SIP ID or SIP password is incorrect.
404 Number unknown	The number doesn't exist, isn't assigned to a connection, or isn't configured in the recipient's device or phone system.
486 Busy	The recipient's line is currently busy.
487 Call ended	Standard signal when the other party hangs up.

Other commonly transmitted codes

100 Trying	Call setup in progress.
180 Ringing	The recipient's device is signaling an incoming call.
183 Session progress	Connection is being established.
200 OK	Call accepted or device registered.
301 Moved permanently	Permanent call forwarding active.
302 Moved temporarily	Temporary call forwarding active.
400 Bad request	Incorrect parameters in the request.
403 Forbidden	No permission to place this call.
407 Proxy authentication required	Authentication needed for outbound calls.
408 Request timeout	No response, possibly due to network issues.
480 Temporarily unavailable	Recipient unavailable (e.g., DND active).
481 Call does not exist	Status message not received.
482 Loop detected	Call forwarding loop detected.
488 Not acceptable here	Unsupported codec, encryption, or transmission method.
500 Server error	General server issue.
502 Bad gateway	Incorrect or faulty gateway.
503 Service unavailable	SIP service temporarily down.
603 Declined	Call rejected manually or automatically.