If someone asks what’s the difference between client failure server failure and global server failure what can be the answers for sip fail cause?
4XX Codes (Client Failure): The request contains bad syntax or cannot be fulfilled at the server e.g. 401 Unauthorized, 403 Forbidden.
5XX (Codes Server Failure): The server failed to fulfill an apparently valid request e.g. 500 Server Internal Error, 504 Server Time-out.
6XX (Global Failure): The request cannot be fulfilled at any server e.g. 600 Busy Everywhere, 604 Does Not Exist Anywhere.