i supose that you are using an abap mapping, and you are in SAP PI stack abap.
In this case u should call it
call function 'RFC_READ_TABLE' DESTINATION 'RFC_ECC'
where RFC_ECC is an entry at SM59 as a type 3.
after that, you should call again the function as mentioned but for BI and after for SRM.
You should have three different RFCs, one for each system,