SIP (Session Initiation Protocol) response codes are three-digit numbers that indicate the outcome of a SIP request. Similar to HTTP, these codes are grouped into classes based on their first digit. Here’s a detailed explanation of each class of SIP codes :
1. 1xx (Provisional): These are provisional or informational responses that indicate the server has received the request and is processing it. They do not represent the final outcome of the request.
100 Trying ⏳: The server received the request and is performing necessary actions to process it.
180 Ringing ?: The callee’s device is ringing, and the user is being alerted about the incoming call.
2. 2xx (Successful) ✅: These response codes indicate that the request was successfully processed and completed.
200 OK ?: The request was successful, and the server has provided the necessary information or performed the required action.
3. 3xx (Redirection) ?: These response codes indicate that the request needs further action to be completed, such as contacting another server or following a redirection.
300 Multiple Choices ?: There are multiple options available to reach the callee, and the caller needs to choose one.
301 Moved Permanently ➡️: The callee’s address has permanently changed, and the caller should use the new address provided in the response.
4. 4xx (Client Error) ❌: These response codes indicate that the request contains bad syntax or cannot be fulfilled by the server.
400 Bad Request ?: The request is malformed or contains incorrect information.
404 Not Found ?: The requested user or server was not found or does not exist.
5. 5xx (Server Error) ⚠️: These response codes indicate that the server failed to fulfill a valid request.
500 Internal Server Error ?: The server encountered an error while processing the request and could not complete it.
503 Service Unavailable ?: The server is temporarily unable to process the request, usually due to overloading or maintenance.
6. 6xx (Global Failure) ?❗: These response codes indicate that the request cannot be completed by any server and must be considered a global failure.
600 Busy Everywhere ?: The callee cannot be reached on any of the available addresses or devices.
603 Decline ?♂️: The callee has explicitly declined the call, and no alternative addresses are available.
By understanding these SIP response codes and their meanings, you can better diagnose and troubleshoot issues in SIP-based communication systems. ???