How is the process/procedere inside XI (receiving IDOC)

Hello,

I would like to have a deeper look inside XI.

What is the first step when the IDoc arrives?

Find a service? How does the IE find the service?

What is the IE going to do next (receiver-agreement, receiver-determination, communication channel)?

I guess a lot of users would appreciate that!

Is the a document where a the steps described in detail?

Thanks a lot

regards mario