The human-machine interface, one of the core elements of an automation system, is built with several Siemens alternatives. In control rooms treated as the main centre of the automation system, redundant server/client structures can be set up on industrial PCs or on more economical solutions. Users at remote locations can connect to the main system over the internet with Web Navigator. Within these structures an engineering PC—sometimes the server PC, sometimes a separate PC—can carry out engineering work and join it to the system.