SIP 204 No Notification vs 421 Extension Required
SIP 204 (No Notification) is a 2xx Success response, while 421 (Extension Required) is a 4xx Client Failure response. 204 indicates that the request was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request. 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 was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request.
Cuándo lo verás
When subscribing to event packages that may not generate immediate notifications, such as dialog or presence packages.
Cómo solucionarlo
No fix needed. The subscription was accepted but there is no state change to notify about yet.
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
204 is a 2xx Success response, while 421 is a 4xx Client Failure response.
SIP 204: The request was successful but the server has decided not to send a NOTIFY for this SUBSCRIBE request.
SIP 421: The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
You encounter 204 when when subscribing to event packages that may not generate immediate notifications, such as dialog or presence packages.
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 204 (No Notification): No fix needed. The subscription was accepted but there is no state change to notify about yet. 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.