In RFC communication between an external program and a SAP system having a user who only has authorization in the SAP systems is necessary. Depending on the technology that the program uses for communication the attaches R/3 or SAP system is released. The SAP user sets external program which requires different authorizations.
External programs can essentially use various technologies for RFC communication. Most of them provide respiratory services which dynamically read the interface definition of a remote-enabled function module from the ABAP Data Dictionary.