Hi Pavan,
My apology for late response here. I will suggest use SOAP as sender adapter and RFC as Reviver to integrate Ariba. Please see the below diagram.
Can you please tell me which product of Ariba you are integrating with SAP, Ariba has On-demand as well as On-premise also Ariba network. I believe on your projects Ariba consultant will be working with you , you ask the Ariba SAP integration documents provided by Ariba.
Anyways I will mail you the documents to your email address.
