603 — SIP call declined
Domain : SIP
What does this error mean?
The destination explicitly declines the call and indicates no alternate branch should be tried.
Where can it appear?
This error may appear in application logs, client messages, monitoring systems or protocol traces. Keep the complete timestamp, request context and surrounding events before troubleshooting.
Likely causes
- Endpoint or trunk state
- SIP routing, NAT or firewall behavior
- SDP, codec or policy mismatch
Checks and resolution
- Capture and read the SIP ladder around the failure
- Check registration, trunk and routing status
- Compare SDP/codecs and network reachability
Caution : Avoid opening broad port ranges or disabling security controls just to make a call complete.