In an internal procedure call, the called unit is part of the calling program. The source code of the called unit is either part of the source code of the calling program or attached to it as an include program. This means that, at runtime, no other programs have to be loaded into the internal session of the calling program.
All procedures - subroutines, function modules, and methods - can be called internally in the program in which they are defined.
· Using an internal call is the recommended and most frequently used method of calling a subroutine.
· Function modules can only be called internally if a function module calls another function module from the same group. Otherwise, function modules are called externally.
· Methods are called internally when a class calls one of its own methods, or when you use a method of a local class in an ABAP program.