Synchronous RFC (sRFC)

• 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.