An ATM network is a set of conversations: status, transactions, configuration, updates. Those conversations travel across distance. Encryption and authentication are how the center knows it is talking to the right machine, and how the machine knows it is talking to the right center.
What “encrypted communication” means here
Operational and transactional messages should not travel in plaintext. Endpoints should be identifiable. The public description stops there. The implementation is not a marketing exhibit.
Why monitoring still matters
Encryption protects content. It does not tell you that a door opened. Communication security and operational monitoring are complementary.