RFC is used to communicate between SAP systems and SAP to Non-SAP systems using TCP/IP protocol. RFC's are defined in [SM59]. There are 4 types of RFC's
1. Asynchronous RFC
2. Synchronous RFC
3. Transactional RFC
4. Queue RFC
1. Asynchronous RFC - (Like a post card). The sending system may or may not receive it. i.e. there is no acknowledgement from the receiving . The transmission is not reliable.
2. Synchronous RFC - It is not like ARFC. It gets an acknowledgement from the target system. (like a register post).
If the receiving system is not available the process goes into RFC/ CPIC/ Sleep mode and waits until it is wakened by the target system. Target system/ Receiving system may be busy i.e. all the resources are used up. This is reliable but time consuming and expensive (Client Copy) the job should get finished.
Note: SAP uses CPIC protocol SAP specific (Common Programming Interface for Communication) to communicate between system.
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