The document describes different payment system schemes involving card payments and interchange fees. In the basic scheme, when a customer pays a merchant using a card, the card issuer receives $98.40, pays the merchant $97, and pays the payment system $99 while the customer pays $100. The document then outlines 4 versions of a payment system where a bank acts as both issuer and acquirer, handling authorization processing either in-house or through a third-party service provider while working with card schemes. Across the versions, responsibilities for transaction routing, software support, and merchant terminal management are allocated between the bank, potential software developers, and service providers.