[teilo]

The entire system is built around asynchronous batch processing, as one would expect given when it was designed.

It assumes intermittent serial connections between systems to transfer the payload. The systems then process the payload offline, generate a response, and send back the result during the next transfer window.

Nowadays this is done via the Internet,* but the same basic architecture, and in many cases, the same mainframe backends, are still being used to do the processing.

* I'm not sure how the banks and the Fed are connected, actually. But ACH from businesses almost always go over the Internet. They used to go over dialup.