SIP 100 Trying vs 500 Server Internal Error
SIP 100 (Trying) is a 1xx Provisional response, while 500 (Server Internal Error) 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, 500 means that the server encountered an unexpected condition that prevented it from fulfilling the request.
Description
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.
When You See It
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.
How to Fix
No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.
Description
The server encountered an unexpected condition that prevented it from fulfilling the request.
When You See It
When the SIP server has an internal error — database failure, unhandled exception, or resource exhaustion.
How to Fix
Check server logs for the specific error. Common causes include database connectivity issues, configuration errors, or memory exhaustion.
Key Differences
100 is a 1xx Provisional response, while 500 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 500: The server encountered an unexpected condition that prevented it from fulfilling the request.
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 500 when when the SIP server has an internal error — database failure, unhandled exception, or resource exhaustion.
When to Use Which
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 500 (Server Internal Error): Check server logs for the specific error. Common causes include database connectivity issues, configuration errors, or memory exhaustion.