Hi Pratheep,
Please Maintian Define below prerequisites..
Connect SAP NetWeaver Gateway to your back-end system (Trusted RFC)Connection Settings: SAP NetWeaver Gateway to SAP Systems
Connect your back-end system to SAP NetWeaver Gateway (Trusted RFC)Connection Settings on the Back-End System
Once you have maintained above steps. create system alias in NW gateway server connected to ECC RFC Destination.
Regards
Naresh