SIP 302 Moved Temporarily vs 421 Extension Required
SIP 302 (Moved Temporarily) is a 3xx Redirection response, while 421 (Extension Required) is a 4xx Client Failure response. 302 indicates that the callee has temporarily moved to a different address. The client should retry the request at the Contact address but continue using the original URI for future requests. 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.
Description
The callee has temporarily moved to a different address. The client should retry the request at the Contact address but continue using the original URI for future requests.
When You See It
When a user is temporarily reachable at a different location, such as when traveling or using a different device.
How to Fix
Redirect the current call to the Contact URI provided, but keep the original URI for future requests.
Description
The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
When You See It
When the server requires a specific SIP extension that the client did not indicate support for.
How to Fix
Add the required extension to the Supported header and ensure your UA implements it. Check the response for which extension is needed.
Key Differences
302 is a 3xx Redirection response, while 421 is a 4xx Client Failure response.
SIP 302: The callee has temporarily moved to a different address. The client should retry the request at the Contact address but continue using the original URI for future requests.
SIP 421: The UAS needs a particular extension to process the request but the extension is not listed in the Supported header.
You encounter 302 when when a user is temporarily reachable at a different location, such as when traveling or using a different device.
You encounter 421 when when the server requires a specific SIP extension that the client did not indicate support for.
When to Use Which
For 302 (Moved Temporarily): Redirect the current call to the Contact URI provided, but keep the original URI for future requests. 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.