ALE - Basics

ALE is Application Link Enabling - An middleware tool. Data is exchanged asynchronously, except for reads which are only synchrous. 

ALE is a SAP proprietary technology that enables data communication between two or more SAP R/3 and/or external systems. ALE comes with application distribution/integration scenarios as well as a set of tools, programs, data definitions, and methodologies that you can easily configure to get an interface up and running. The ALE components are inherently integrated with SAP applications and are robust, leading to a highly reliable system. ALE provides mechanisms using which clients can achieve integration as well as distribution of applications and data. 

The Settings can be done in SPRO ® SAP Reference IMG ® Application Server -> IDoc Interface/ALE

To use the ALE tools choose Tools ® IDoc Interface/ALE