The ABAP statements CALL TRANSACTION (start a new transaction), SUBMIT (start an executable program), and CALL FUNCTION... DESTINATION (call a function module using RFC) open a new SAP LUW. When you call a program, it always opens its own SAP LUW. However, it does not end the LUW of the SAP transaction that called it. This means that a COMMIT WORK or ROLLBACK WORK statement only applies to the SAP LUW of the called program. When the new LUW is complete, the system carries on processing the first SAP LUW.

When you call a function module asynchronously using the CALL FUNCTION <function> STARTING NEW TASK ' ' statement, it runs in its own SAP LUW.

The CALL FUNCTION... STARTING NEW TASK statement calls a function module asynchronously in a new session. Unlike normal function module calls, the calling transaction carries on with its own processing as soon as the function module has started, and does not wait for it to finish processing. The function call is asynchronous. The called function module can now call its own screens and interact with the user.

Transactions in this form consist entirely of processing blocks (dialog modules, event blocks, function module calls, and subroutines). You should be careful to ensure that external subroutines or function modules do not lead to COMMIT WORK or ROLLBACK WORK statements accidentally being executed.