An ATM controller (ATMC) is a system used in financial institutions to route financial transactions between ATMs, core banking systems and other banks.
An ATM controller is key infrastructure in an interbank network.
It would then forward the message to Bank A's ATMC for authorisation.
ATMCs make use of a SAF (store and forward) queue to ensure transactions are not lost.
An ATMC will usually have at least one attached hardware security module to manage the keys relating to PIN validation and encryption of connections.