The classic way for communication between non-SAP systems and SAP is, according to SAP itself, the RFC interface. RFC interfaces are also often used to communicate between SAP systems itself. Put simply, RFC is a remote function call. The RFC interfaces for integration have been available since SAP/R3 until today. With RFC, there is an RFC client and an RFC server, whereby the client calls a function on the server. The function is executed on the remote system. In an RFC coupling, both systems can act as server and client. The call of an RFC function is synchronous, so that it is especially suitable for processes in which decisions or data are directly required for production. The OPC Router can call RFC interfaces in the SAP system using all parameter types and data, but it can also be configured as an RFC server and serve as a call target.
Example RFC in SAP SE80