How Do You Diagnose?

An industrial machine builder is thinking about upgrading to digital networks for communications among the controller, the I/O, sensors and maybe drives, but they're concerned about diagnosing network faults and monitoring network performance on the machine. Are there software and hardware tools they'll need to install directly on their machines? Which handheld tools can their techs and their customers’ techs use to check out digital networks? How much training should they expect their support personnel will need?