1. Creating a logical system (BD54)
Every SAP R/3 client used for ALE/RFC must have a base logical system (LS) associated with the SAP client.
Every base LS becomes the sender for outbound messages and a receiver for inbound messages.
In addition to the base LS, additional logical system(s) must be created within that SAP R/3 system for every SAP R/3 and external system used for ALE interfaces. In an inbound ALE/RFC interface, this second LS represents the sender with respect to the base LS. In an outbound ALE/RFC interface, this second LS is a receiver.
A logical system may be created for each external system that communicates with SAP R/3. The design of your maps and systems dictate what is an external system. Generally, you create an external system to correspond to each distinct non-SAP system.
Transaction BD54 creates a logical system to represent the server system for the distribution of data to and from the SAP R/3 system.
To create a logical system