I can certainly appreciate the desire to roll your own solution without using the OnRamp, but questions such as this are precisely why I would recommend using the OnRamp. This has all been figured out and implemented already.
The interactions are all defined within the cXML spec. The low-level interactions are sync while the higher levels are async. For example, the punchout process is a combination where the user is “handed off” to your site from the Ariba network (sync), the user shops and fills the shopping cart, and then your site sends the checked-out cart back to the procurement app via the Ariba network (async).
It’s been a few years since I’ve done Ariba stuff so someone please correct me if I’m off on my description.
#Integration-Server-and-ESB#Adapters-and-E-Standards#webMethods