The response codes are consistent with, and extend, HTTP/1.1 response codes. Not all HTTP/1.1 response codes are appropriate, and only those that are appropriate are given here. Other HTTP/1.1 response codes should not be used. Also, SIP defines a new class, 6xx.
SIP/2.0 allows six values for the first digit; from the SIP Rfc:
- 1xx: Provisional — request received, continuing to process the request. Provisional responses, also known as informational responses, indicate that the server contacted is performing some further action and does not yet have a definitive response. A server sends a 1xx response if it expects to take more than 200 ms to obtain a final response. Note that 1xx responses are not transmitted reliably. They never cause the client to send an SIP method ack. Provisional (1xx) responses MAY contain message bodies, including session descriptions.
- SIP Response class2: Success — the action was successfully received, understood, and accepted;
- SIP Response class3: Redirection — further action needs to be taken in order to complete the request;
- SIP Response class4: Client Error — the request contains bad syntax or cannot be fulfilled at this server;
- SIP Response class5: Server Error — the server failed to fulfill an apparently valid request;
- SIP Response class6: Global Failure — the request cannot be fulfilled at any server.
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December 2, 2021
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