What it is RFC?

Communication between applications in different systems in the SAP environment includes connections between SAP systems as well as between SAP systems and non-SAP systems. Remote Function Call (RFC) is the standard SAP interface for communication between SAP systems. RFC calls a function to be executed in a remote system.
Synchronous RFC

The first version of RFC is synchronous RFC (sRFC). This type of RFC executes the function call based on synchronous communication, meaning that the systems involved must both be available at the time the call is made.
Transactional RFC (tRFC)

Transactional RFC(tRFC, previously known as asynchronous RFC) is an asynchronous communication method that executes the called function module just once in the RFC server. The remote system need not be available at the time when the RFC client program is executing a tRFC. The tRFC component stores the called RFC function, together with the corresponding data, in the SAP database under a unique transaction ID (TID).

If a call is sent, and the receiving system is down, the call remains in the local queue. The calling dialog program can proceed without waiting to see whether the remote call was successful. If the receiving system does not become active within a certain amount of time, the call is scheduled to run in batch.

tRFC is always used if a function is executed as a Logical Unit of Work (LUW). Within a LUW, all calls

· are executed in the order in which they are called

· are executed in the same program context in the target system

· run as a single transaction: they are either committed or rolled back as a unit.

Implementation of tRFC is recommended if you want to maintain the transactional sequence of the calls.

Disadvantages of tRFC

· tRFC processes all LUWs independently of one another. Due to the amount of activated tRFC processes, this procedure can reduce performance significantly in both the send and the target systems.

· In addition, the sequence of LUWs defined in the application cannot be kept. It is therefore impossible to guarantee that the transactions will be executed in the sequence dictated by the application. The only thing that can be guaranteed is that all LUWs are transferred sooner or later.
Queued RFC (qRFC)

To guarantee that multiple LUWs are processed in the order specified by the application, tRFC can be serialized using queues (inbound and outbound queues). This type of RFC is called queued RFC (qRFC).

qRFC is therefore an extension of tRFC. It transfers an LUW (transaction) only if it has no predecessors (based on the sequence defined in different application programs) in the participating queues.

Implementation of qRFC is recommended if you want to guarantee that several transactions are processed in a predefined order.