There is a lot of information to be found about SWIFT and the protocols that are being used by its members to exchange messages. However, I could not find much information about how banks and businesses are physically connected to the network and how it is built itself. I imagine the core network as a large private (IP) network with hard- and software in specific company locations/data centers which is, like many others, connected via the numerous networking exchanges/peering points using fiber optical and other links. The institutions could then connect via some kind of VPN gateway over the public internet or could themselves have dedicated lines which are again connected to one of the network exchanges. Or, of course, there could be both or more implementations. Does anyone have some insight into this?
Additionally, I am also be interested in the same kind of information concerning the exchange of SEPA messages in Europe.