Why is SAP Process Integration needed?

SAP ECC or SAP S/4HANA don’t usually expose their functions directly to third-party systems. For this reason, SAP Process Integration is introduced to provide SAP functions to third-party systems and consume third-party system functions in SAP.

SAP Process Integration server opens a port to provide and consume web services from and to SAP. So, there is no need to open a port in SAP ECC or SAP S/4HANA for this purpose.