Ask HN: Where to learn about payments infrastructure?

There's lots going on in payments sector,from traditional banks, fintech startups all the way to Blockchain on the other end of the spectrum. What are good resource out there to learn more about it? For instance, how stripe talks to banks? How PayPal can connect to banks in many countries? How payment gateways work under the hood? What MasterCard/Visa do that others can't and etc.