Three transfer objects are available in the SAP system Plug-in for connecting with RFC, BAPI and IDoc.
An RFC is used to call-up a function in an SAP system. Import and export parameters of several types can be used (simple, structures, tables). The calls get executed synchronously.
BAPIs are standard interfaces of the SAP system and allow access to methods of business objects. As with RFCs, functions and their parameters (simple, structures, tables) get addressed. The call is also synchronous.
The IDoc data format addresses asynchronous data transmission. IDocs represent structured documents used to send and receive transaction-based data to and from the SAP system.