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. |