Remote Function Call (RFC)
This interface is logically above CPI-C. It simplifies the implementation of communication processes by relieving the programmer of the task of writing his own communication routines.
The RFC interface enables function calls between two SAP systems (R/3 or R/2), or between an SAP system and an external one. The RFC library functions support the C programming language and Visual Basic (on Windows platforms).
In the case of asynchronous RFC, calls are also transmitted to remote systems when the target system is not active or momentarily cannot be reached (analog to Q-API).
For more details on this interface, refer to the following documentation: