Receiving Transfer Orders 
The following overview illustrates how transfer orders are received.
Formatting and Sending Data
The most important task of the external system is, of course, to communicate with terminal equipment such as fork-lift control systems, control systems in general, handheld terminals for mobile data entry etc. The subject of this discussion is, however, the communication that takes place with the SAP R/3 system after the data has been generated in the external system. The tasks performed with regard to this are described below:
Buffer and prepare data in IDoc format
Refer to the appropriate documentation for details on defining the IDoc and the structure of the various IDocs.
Call a central function module in R/3 by means of a send program
You will also require the RFC library as a programming aid for the send program. The central function module is once again part of the ALE layer.
It is possible for several IDocs to be transferred in one communication process, i.e. in one R/3 function module call. There are, however, IDoc types which can only be sent individually. Explicit reference will be made to this in the descriptions of the IDocs concerned.
Update the IDocs accordingly once they have been sent
The external system must also manage the status of the data sent during the transmission procedure. The IDoc must be resent if it is not sent successfully the first time.
Double transmission of the IDocs must also be prevented on the SAP side. The transaction ID is used for this purpose. This is assigned for each communication process on the SAP side. The data which was transferred by the external system must always be sent with this transaction ID (refer also to the technical documentation for the RFC). The same transaction ID must also be used if the IDoc is resent.
The IDoc number is not used on the SAP side to check for double transmissions.
Receive and Post the Data
ALE receives the IDoc and writes it to the database. A receipt confirmation is sent back to the external system once the data has been buffered. The IDoc is then passed on to the application where it is then processed.
The application, in this case for generating the transfer order, sends one status per IDoc back to the ALE. This IDoc status forms the basis for the initiation of a possible error processing procedure.
Error Processing
The following errors can occur:
It is temporarily not possible to establish a connection.
The external system should also ensure, via status management, that reposting is possible.
Error in the ALE layer
An IDoc has been generated but it is not possible to initiate processing.
This is the same as the error that occurs during transmission from the WM system if the syntax of the IDoc received is incorrect or if the partner profile of the input for the sender and message type of this IDoc is missing. Further details on this error can be found in the section
SAP System Settings and Modification Concept.Error in the application (e.g. when a transfer order is posted)
This is a logical error in the application. A message is sent to a position using the above-mentioned status in the IDoc. Several users can be assigned to a position. The users receive the error message in their respective SAP OFFICE inbox. The message disappears from the other inboxes as soon as one of the users picks it up and processes it.