B2B, trade of products or services, between a wholesale and a retailer often consists of a varying transaction size as opposed to manufacturer -> wholesale which often work with big transactions. 

The wholesale is the supplier and the retailer is the customer in this case.

Being a supplier in this kind of B2B chain is less complex since there is often refined products being traded.

The customer is in his turn often performing directly against end customers (and ends the supply chain going from B2B to B2C)

Trading documents or information between the organisation is often sent through fax or some kind of integration message between procurement systems or directly between ERP systems.