SIP 180 Ringing vs 421 Extension Required
SIP 180 (Ringing) is a 1xx Provisional response, while 421 (Extension Required) is a 4xx Client Failure response. 180 indicates that the UA receiving the INVITE is trying to alert the user. This response is used to initiate local ringback tone at the caller's end. 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.
Descrição
The UA receiving the INVITE is trying to alert the user. This response is used to initiate local ringback tone at the caller's end.
Quando você o vê
During call setup when the callee's phone is ringing. You should hear a ringback tone after receiving this response.
Como corrigir
No fix needed — the callee's device is ringing. If the call never connects after ringing, check the callee's device or call forwarding settings.
Descrição
The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
Quando você o vê
When the server requires a specific SIP extension that the client did not indicate support for.
Como corrigir
Add the required extension to the Supported header and ensure your UA implements it. Check the response for which extension is needed.
Diferenças principais
180 is a 1xx Provisional response, while 421 is a 4xx Client Failure response.
SIP 180: The UA receiving the INVITE is trying to alert the user. This response is used to initiate local ringback tone at the caller's end.
SIP 421: The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
You encounter 180 when during call setup when the callee's phone is ringing. You should hear a ringback tone after receiving this response.
You encounter 421 when when the server requires a specific SIP extension that the client did not indicate support for.
Quando usar qual
For 180 (Ringing): No fix needed — the callee's device is ringing. If the call never connects after ringing, check the callee's device or call forwarding settings. 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.