SIP - Response Codes
A SIP response is a message generated by a user agent server (UAS) or SIP server to reply a request generated by a client. It could be a formal acknowledgement to prevent retransmission of requests by a UAC.
A response may contain some additional header fields of info needed by a UAC.
SIP has six responses.
1xx to 5xx has been borrowed from HTTP and 6xx is introduced in SIP.
1xx is considered as a provisional response and the rest are final responses.
|S.No.||Function & Description|
|1||1xx: Provisional/Informational Responses
Informational responses are used to indicate call progress. Normally the responses are end to end (except 100 Trying).
|2||2xx: Success Responses
This class of responses is meant for indicating that a request has been accepted.
|3||3xx: Redirect Responses
Generally these class responses are sent by redirect servers in response to INVITE. They are also known as redirect class responses.
|4||4xx: Client Failure Responses
Client error responses indicate that the request cannot be fulfilled as some errors are identified from the UAC side.
|5||5xx: Server Failure Response
This class response is used to indicate that the request cannot be processed because of an error with the server.
|6||6xx: Global Failure Response
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.