Availability Check Using External Systems
You can also use SAP-external software for the availability check. You connect an external system with SAP CRM to execute an availability check or to get availability information.
You can find more information under availability check and availability information.
Integration
A series of Business Add-Ins (BAdIs) is available for the connection of an external system to SAP CRM for the availability check. The BAdIs are located in the Implementation Guide (IMG) for Customer Relationship Management
under 
Basic Functions
Availability Check
Availability Check / Info Using External ATP System
.
You need to implement the BAdIs that contain the necessary logic to connect the required external system and to provide it with the necessary input data.
Features
Note
You must decide for each client whether you want to carry out an availability check or obtain availability information. A combination of the two functions within one client is not possible.
These BAdIs are designed for a single SAP CRM system and a single external system. If you need to use several external systems, you must provide determination logic for the distribution. When the results of the availability check are transferred back to SAP CRM, it must look as if the data was processed by only one external system.