Entering content frameBackground documentation Data Flow: WMS Receives Data Locate the document in its SAP Library structure

The data flow across the interface between the Warehouse Management system (WMS) and the external system (WMS-WCU interface) is explained using the example of the communication flow for transferring data relevant to a transfer order (TO) from the external system to the WMS.

For further information on the business background, see Scenarios for Connecting External Systems.


You have defined the necessary TCP/IP settings. For more information, see Structure linkBC - SAP Communication: Configuration.

You have defined the ALE interface in the Customizing for Warehouse Management under Interfaces ® External Systems ® Configure Warehouse Management ® Warehouse Management View ® Activate Interface per Whse Number.

Process Flow

  1. The external system saves the data relevant for transferring to the SAP system and formats it in an IDoc.
  1. The external system transfers the IDoc with an appropriate program.

The transfer is based on the Remote Function Call. For more information, see Basis ® Basis Services/Communication Interface ® Remote Communications ® The RFC API ® Structure linkProgramming with the RFC API.

The central function module is in the ALE layer. As soon as the external system calls the function module on the SAP system side, the external system can transfer several IDocs.


If an IDoc type is only designed to be transferred individually, this is noted in the relevant IDoc system documentation.

  1. Status management for the data to be transferred should prevent the external system from not transferring data.
  2. Note

    If the system cannot successfully transfer IDocs, you must ensure that these IDocs are transferred again at a later time.

  3. The SAP system should be able to recognize IDocs that have been transferred by the external system already. This is made possible by the unique transaction identification number (transaction ID), which the SAP system assigns for each communication process. For more information, see Basis ® Basis Services/Communication Interface ® Remote Communications ® The RFC API ® Structure linkTransactional RFC Client Programs.

The external system must always provide the transferred data with this transaction ID. If the external system transfers an IDoc for a second time due to unsuccessful communication at an early time, the external system must issue the same transaction ID again.


The SAP system does not use the IDoc number to recognize a double transfer of IDocs from the external system.

  1. The SAP system receives the transferred IDoc via ALE, saves the IDoc in the database, and confirms receipt of the IDoc to the external system.
  2. ALE transfers the IDoc to WMS asynchronously on receipt of the IDoc and the WMS takes over the processing of the IDoc.
  3. The WMS creates transfer orders on the basis of the transferred data.
  4. For each IDoc, the WMS reports a processing status back to ALE.

On the basis of the processing status, ALE triggers error processing of the IDoc where necessary.

Error Processing

When you receive an IDoc in the WMS from an external system, the following problems may occur:



What You Should Know

There is no connection between the external system and the SAP system

Using status management, the external system should ensure that IDocs can be transferred again at a later time.

Error in the ALE interface:

There are syntactical errors in the data that the external system sent to the ALE

ALE adopts the IDoc and saves it, but cannot transfer the IDoc to the WMS for processing. For more information, see IDoc Error Processing.

Error in the ALE interface:

  • Inbound partner profile for the sending system
  • IDoc message type

are not defined

For more information, see IDoc Error Processing.

Application errors in the WMS

If errors occur in the processing of the received IDoc, the WMS transfers the processing status correspondingly. For more information, see Processing Logical IDoc Errors in the WMS.



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