Introduction: The objective of this blog is to share my insights on the topic of S/4HANA migration for the Warehouse Control Unit interfaces (WM-LSR) in the classical SAP LE-WM of legacy ECC system.

The control of material movements in the warehouse is hardly carried out manually but by an automated warehouse control units (WCUs). The task of the WCU is to control and monitor the warehouse automation like conveyor systems, automatic loading and unloading equipments etc.

In certain cases, WCU interface messages are not only used for WCU integration but even to integrate other third part warehouse systems like that of 3PL.

As shared in my earlier blog, What Options to Consider if Legacy LE-WM is Not Compliant for Stock Room Management during S/4HANA Migration?

Warehouse Control Unit (WCU) Interfaces are implemented in LE-WM either via standard ALE IDOC Interface approach or via RFC approach (IMG configuration driven settings), however this is now no longer a part of the the SAP recommended architecture within SAP S/4HANA; since LE-WM itself is now trimmed down to a basic WM in S/4HANA in the form of stock room management.

However, If it is still decided by the organization to migrate classical ECC LE-WM by using Stock Room Management in S/4HANA, this strategy would first requires to make such warehouse first fully compliant by removing non-compliant configuration of WCU configuration. Removal of such non-compliant configuration requires the alternative solution implementation in ECC LE-WM in the form of pre-project, this custom solution will help by retaining the these WCU interfaces even after S/4HANA migration and at the same time making ECC LE-WM warehouses fully compliant with S/4HANA Stock Room Management.

Step 1: Removal of WM-LSR configuration in ECC LE-WM

Below important configuration settings should be reviewed in legacy ECC system and either removed or deactivated in order to make warehouse number compliant with Stock Room Management.

1a. Main IMG node for setting up WM-LSR interfaces

1b. Warehouse Number Activation Config. for WM-LSR interfaces

1c. ECC to External System Interface Configuration

After deactivating and removing above config. settings, proceed to the next step of implementing alternative solution to integrate WCUs with ECC.

Step 2: Implement key WM user-exits in ECC to replace standard WM-LSR approach for Integration with WCU

Some user  exits in LE-WM, for example as given below that are used to send warehouse tasks to WCU towards end of transfer order creation for the outbound transmission of IDocs, can be considered.

• Enhancement MWMTO001 (Enhancements for end of transfer order generation)
• Function exit EXIT_SAPLL03T_001

Standard WM-LSR (WCU config.) provided WMTORD can be replaced with ZWMTORD and this Z-IDoc can be triggered and filled after Transfer Order (TO) is saved.

• Enhancement MWMTO002 (Enhancements at end of transfer order confirmations)
  Function exit EXIT_SAPLL03T_002

Standard WM-LSR (WCU config.) provided WMTOCO can be replaced with ZWMTOCO (can be Inbound/outbound both) and this Z-IDoc can either be used to confirm Transfer Orders or send already confirmed Transfer Orders to WCU.

Step 3: Migrate LE-WM custom code during ECC system conversion to S/4HANA 

As part of overall S/4HANA migration execution, especially using the SPAU/SPDD step after the system conversion step is completed, one can adjust these already implemented custom user-exists, if needed.

Once these custom objects are migrated and available in S/4HANA too, S/4HANA is now ready to send Stock Room Management triggered custom IDocs to WCU and also to receive it from WCU.

Conclusion: LE-WM can be converted into Stock Room Management compliant during S/4HANA migration, provided that the non-compliant component like WM-LSR used in WCU integration is deactivated and removed, plus an alternative solution is implemented in LE-WM as a pre-project prior to S/4HANA migration for triggering, filling and transmitting custom developed IDocs to WCU.