SIP Response Codes

When working with the Session Initiation Protocol (SIP), response codes are an important part of the communication between user agents and servers. These codes indicate the status of a request and are used to determine the next steps in establishing a session.

SIP Response Categories

SIP response codes typically fall into one of the following categories:

• 1xx - Informational responses
• 2xx - Successful responses
• 3xx - Redirect responses
• 4xx - Client error responses
• 5xx - Server error responses
• 6xx - Global failures

Within each category, there are specific response codes that provide more information about the status of a request.

Examples

Here are a few examples of common SIP response codes:

• 100 Trying - Indicates that the server has received the request and is processing it, but has not yet sent a final response.
• 180 Ringing - Indicates that a call is being forwarded or an agent is ringing before answering a call.
• 200 OK - Indicates that the request was successful and that the server has fulfilled it.
• 301 Moved Permanently - Indicates that the requested server has moved permanently and provides the new address.
• 401 Unauthorized - Indicates that the request requires authentication and that the client must provide valid credentials.
• 500 Internal Server Error - Indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.
• 600 Busy Everywhere - Indicates that all possible destinations for a call are busy.

Conclusion

SIP response codes are an essential part of SIP communication, as they enable user agents and servers to quickly and reliably establish sessions. By understanding these response codes and their implications, developers can create more robust and effective SIP applications.