SIP 200 OK vs 421 Extension Required
SIP 200 (OK) is a 2xx Success response, while 421 (Extension Required) is a 4xx Client 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, 421 means that the UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
Descripción
The request has succeeded. For INVITE, the call has been answered. For other methods, the action has been completed successfully.
Cuándo lo verás
When a call is answered (INVITE 200 OK), a registration succeeds (REGISTER 200 OK), or a subscription is accepted (SUBSCRIBE 200 OK).
Cómo solucionarlo
No fix needed — this is a success response. The caller should send an ACK to complete the three-way handshake for INVITE transactions.
Descripción
The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
Cuándo lo verás
When the server requires a specific SIP extension that the client did not indicate support for.
Cómo solucionarlo
Add the required extension to the Supported header and ensure your UA implements it. Check the response for which extension is needed.
Diferencias clave
200 is a 2xx Success response, while 421 is a 4xx Client 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 421: The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
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 421 when when the server requires a specific SIP extension that the client did not indicate support for.
Cuándo usar cada uno
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 421 (Extension Required): Add the required extension to the Supported header and ensure your UA implements it. Check the response for which extension is needed.