overview of ACH (old system) https://achdevguide.nacha.org/how-ach-works

the new system will use a closed blockchain network. a federated blockchain based network will be used where nodes are banks and consensus rules are written and controlled by the fed. banks will just be signatories for individual transactions and if supply needs to be increased by issuing new tokens (dollars) then it will be issued by the fed to the banks. Banks will use this for interbank settlement at first for a small number of accounts