SIP
100 Trying
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 This Code
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.