SIP 200 OK vs 501 Not Implemented
SIP 200 (OK) is a 2xx Success response, while 501 (Not Implemented) is a 5xx Server Failure response. 200 indicates that the request has succeeded. For INVITE, the call has been answered. For other methods, the action has been completed successfully. In contrast, 501 means that the server does not support the functionality required to fulfill the request. The method is recognized but not implemented.
Description
The request has succeeded. For INVITE, the call has been answered. For other methods, the action has been completed successfully.
When You See It
When a call is answered (INVITE 200 OK), a registration succeeds (REGISTER 200 OK), or a subscription is accepted (SUBSCRIBE 200 OK).
How to Fix
No fix needed — this is a success response. The caller should send an ACK to complete the three-way handshake for INVITE transactions.
Description
The server does not support the functionality required to fulfill the request. The method is recognized but not implemented.
When You See It
When the SIP method is valid but the server has not implemented it (e.g., INFO, UPDATE, PRACK on a basic server).
How to Fix
Use a different method that the server supports. Check the Allow header in responses to see supported methods.
Key Differences
200 is a 2xx Success response, while 501 is a 5xx Server Failure response.
SIP 200: The request has succeeded. For INVITE, the call has been answered. For other methods, the action has been completed successfully.
SIP 501: The server does not support the functionality required to fulfill the request. The method is recognized but not implemented.
You encounter 200 when when a call is answered (INVITE 200 OK), a registration succeeds (REGISTER 200 OK), or a subscription is accepted (SUBSCRIBE 200 OK).
You encounter 501 when when the SIP method is valid but the server has not implemented it (e.g., INFO, UPDATE, PRACK on a basic server).
When to Use Which
For 200 (OK): No fix needed — this is a success response. The caller should send an ACK to complete the three-way handshake for INVITE transactions. For 501 (Not Implemented): Use a different method that the server supports. Check the Allow header in responses to see supported methods.