SIP Error Codes

• 401 Unauthorized
• 403 Forbidden
• 404 Not Found
• 407 Proxy Authentication Required
• 476 Unresolvable destination
• 480 Temporarily Unavailable
• 483 Interval Too Brief
• 484 Address Incomplete
• 486 Busy Here
• 487 Request Terminated
• 489 Bad event
• 500 Internal server error
• 503 Service Unavailable
• 603 Declined

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http://www.voip-info.org/wiki/index.php?page=Asterisk+variable+hangupcause