Tom Remberg is chief information security officer for Bane NOR, a state-owned company responsible for the Norwegian national railway infrastructure. He says that in order to avoid adverse business impacts in case of an outage, everything must be duplicated and it must be possible to “take one part of the infrastructure down, maintain and upgrade it, while the other one is running” In a video interview with Information Security Media Group, he discusses the need for “different layers of protection” and “high-availability elements,” so if one of the elements such as a server fails, the service is still available.”]
Source: https://www.govinfosecurity.com/digitizing-securing-norways-railway-network-a-17857