• Definition: A communication method that allows one SAP system (or external system) to call a function module in another SAP system.

• Nature:

  • Technical interface (low-level).

  • Can be synchronous (sRFC), asynchronous (aRFC), transactional (tRFC), or queued (qRFC).

• Usage:

  • Purely for function/module execution between systems.

  • Example: A program in SAP ECC calls a function module in SAP CRM to check stock.

• Flexibility:

  • Any RFC-enabled function module can be called.

  • Developer-defined (not standardized for business logic).

• Limitation:

  • Not business-object aware.

  • Risk of inconsistent or unsafe updates if not carefully handled.

🔹 BAPI (Business Application Programming Interface)

• Definition: A standardized, RFC-enabled method that represents business objects in SAP (like SalesOrder, Material, Vendor).

• Nature:

  • Business-level interface (high-level).

  • Built on top of RFC.

• Usage:

  • For performing business transactions in a safe, consistent way.

  • Example: BAPI_SALESORDER_CREATEFROMDAT2 → creates a sales order.

• Flexibility:

  • Only predefined by SAP (or customer-defined extensions).

  • Provides data validation and ensures business rules are followed.

• Advantage:

  • Stable, upgrade-safe, and officially supported by SAP.

  • Standardized input/output (makes integration easier).

• Default type when you call a function module via RFC.

• The caller program waits until the remote system has completed the function execution and returned the result.

• Example use: Real-time data retrieval (e.g., fetching stock from another SAP system).

• FM execution: CALL FUNCTION 'XYZ' DESTINATION 'SAP_R3'.

2. Asynchronous RFC (aRFC)

• Execution is non-blocking → Caller does not wait for immediate results.

• You can trigger parallel processing by calling multiple aRFCs at the same time.

• Example use: Mass data processing, parallelizing jobs.

• FM execution:

CALL FUNCTION ‘XYZ’ STARTING NEW TASK ‘TASKNAME’
DESTINATION ‘SAP_R3’
PERFORMING callback_form ON END OF TASK.

3. Transactional RFC (tRFC)

• Similar to aRFC, but with transactional reliability.

• Each call is executed exactly once in the target system (using LUWs – Logical Units of Work).

• Stored in SM58 until delivered successfully.

• Example use: Posting documents, ALE/IDoc communication.

• FM execution:

CALL FUNCTION ‘XYZ’ IN BACKGROUND TASK
DESTINATION ‘SAP_R3’.
COMMIT WORK.

4. Queued RFC (qRFC)

• Extension of tRFC, but ensures sequence/order of execution using queues.

• Uses inbound and outbound queues (transactions SMQ1/SMQ2).

• Example use: When sequence matters (e.g., stock transfer must happen before goods issue).

• FM execution: Similar to tRFC, but with queue configuration.

Summary :

So, depending on your scenario:

• Use sRFC for synchronous real-time calls.

• Use aRFC for parallel jobs.

• Use tRFC for reliable background communication.

• Use qRFC when sequence matters.