Procedures can be called internally and externally. While at an internal call the required programm is already loaded, the framework program is loaded to the internal mode of the calling program at the first external call of a procedure of the same ABAP system (if it was not loaded already). Except for the loading of class pools, the event LOAD-OF-PROGRAM is triggered. At an external call of a procedure, mind the split-up of the loaded programs in program groups. The following graphic shows the internal and external calls.
Internally, you can call all procedures that are definable in the same ABAP program and which are visible at the location of the call. Externally, you can call the following procedures of the same ABAP systems:
Statements to call procedures:
These statements fill the parameter interfaces of the procedures and assign return values (with the exception of PERFORM not-class-based exceptions). After duly completion of the call, the system returns to the calling position.