Communication Between R/3 and an Externally Registered Program 
Communication Between R/3 and an Externally Registered Program
Purpose
The SAP program interfaces allow an R/3 System to communicate and exchange data with an external program.
As well as the external programs that are always started anew when they are needed, there is also the new program type
Registered Program.The following topics provide an overview about the prerequisites for the partner systems.
These prerequisites depend on whether R/3 is the calling system or the called system:
From an External Program to R/3 From R/3 to an External Program (registered program)