SIP Response Codes (Quick Summary)




  • 1xx: Provisional response
    • SIP request has been received and we are continuing to process the reques
    • Provisional responses indicate that we are performing some further action and do not have a definitive response yet.
    • For example, a 100 Trying response means that we have received an INVITE and are finding a route for the call.  This will immediately be followed by a 180/183 RINGING which may or may not contain message bodies, including session descriptions for audio connections
  • 2xx: Success
    • An action was successfully received, understood, and accepted
  • 3xx: Redirection
    • Further action needs to be taken by the initiating party in order to complete the request
    • For example, a 302 redirect will direct the party to go somewhere else for the next request
  • 4xx: Client Error
    • We can not process the request due to bad syntax or it cannot be fulfilled at this server
    • This can be seen if an invite is sent to a location which does not know where to route the call.
    • 404 NOT FOUND can be returned when a PBX does not have a route for an inbound call
  • 5xx: Server Error
    • The carrier is unable to fulfill an apparently valid request
    • 503 route advance will instruct a client to try the next route
  • 6xx: Global Failure
    • This is provided if the request cannot be fulfilled
    • 603 DECLINED can mean that the account is suspended or out of credit
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