RFC System Fields
As is the case every time a function module is called, when an RFC is made, the system field sy-subrc is initialized in the calling program, or set to the value that is specified in exception handling. In addition, each time a function module is called remotely, the system fields sy-msgid, sy-msgno, sy-msgty and sy-msgv1 to sy-msgv4 are initialized in the calling program. While a remotely-called function module is being executed, if an error message or termination message is sent using the statement Message, then the exception SYSTEM_FAILURE is triggered in the calling program. You can assign a return value to this for the call. When exceptions occur, these system fields are supplied with the properties of the message.