I'm looking to understand the high-level architecture, topology, protocols and componentry of ATMs and POS systems work with banking institutions worldwide.
I've read several half-way decent articles explaining the architecture to the layperson, including:
- https://money.howstuffworks.com/personal-finance/banking/atm5.htm; and
However these don't quite go into the level of detail I'm looking for and leave me with more questions than answers!
My understanding is that an ATM or POS system (such as the software at a cash register) will communicate directly with a Host Server or sometimes called a Host Switch that performs lots of different functions:
- Message routing
- Edge encryption/decryption
- Assisting in reconciliation
- Assisting in settlement
- Several other functions
Here's where I start to get a little fuzzy. There appear to be 1 and possibly 2 additional hops between this Host Switch and the cardholder's bank:
- An EFT Network, sometimes called an Outsource Network Provider; and
- An Interbank Network
So you authenticate at the ATM and ask to withdraw $100 from your checking account. My understanding of the happy path here is that the ATM connects to its Host Switch and forwards on your request. The Switch forwards this request onto the EFT Network, possibly on to the Interbank Network, and eventually the authenticated request goes to your bank servers, who then debit your account by $100 and forward the response all the way back through the chain to the ATM you're standing in front of. The ATM dispenses your cash.
So first off, if anything I've stated here is a mile off the mark, please begin by correcting me or clarifying! Even if I am correct, can someone help me understand the roles of each of these components (Switch, EFT Network and Interbank Network)?
Assuming I'm more or less correct, then this leaves me with several knowledge gaps:
What protocols for communication are being made between each component here (so, between ATM and Host Switch, between Host Switch and EFT Network, between EFT Network and Interbank Network and between Interbank Network and the Cardholder's Bank)?