SIP 100 Trying vs 504 Server Time-out
SIP 100 (Trying) is a 1xx Provisional response, while 504 (Server Time-out) is a 5xx Server Failure response. 100 indicates that the request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses. In contrast, 504 means that the server did not receive a timely response from an external server it accessed while attempting to process the request. Different from 408 (client timeout).
Descripción
The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.
Cuándo lo verás
Immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.
Cómo solucionarlo
No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.
Descripción
The server did not receive a timely response from an external server it accessed while attempting to process the request. Different from 408 (client timeout).
Cuándo lo verás
When a proxy's request to a downstream server times out. The proxy itself is working, but the next hop is unresponsive.
Cómo solucionarlo
Check the downstream server's availability. Verify DNS resolution for the next-hop domain. Consider adjusting transaction timeout values.
Diferencias clave
100 is a 1xx Provisional response, while 504 is a 5xx Server Failure response.
SIP 100: The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.
SIP 504: The server did not receive a timely response from an external server it accessed while attempting to process the request. Different from 408 (client timeout).
You encounter 100 when immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.
You encounter 504 when when a proxy's request to a downstream server times out. The proxy itself is working, but the next hop is unresponsive.
Cuándo usar cada uno
For 100 (Trying): No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration. For 504 (Server Time-out): Check the downstream server's availability. Verify DNS resolution for the next-hop domain. Consider adjusting transaction timeout values.