The document CiA 421 train vehicle control network describes the communication via the in-vehicle integration network. This profile describes, which application data has to be provided to the in-vehicle integration network by a certain sub-system. In case e.g. all doors shall be closed, the train operating system needs to know, where to hand over the command to the door control system. From a CANopen point of view this means, to which object in the object dictionary of the door controller, the train operating system has to write the “close all door command”. In addition, the door controller needs to know the structure of the command (e.g. which bit covers the demanded action). This information is standardized in the document CiA 421. In addition the in-vehicle integration network may be connected to a WTB-based train control network via a gateway device. In order to minimize the formatting effort within such a gateway device, the data defined in CiA 421 was harmonized with those defined in UIC leaflet 556.

The CiA 421 series of documents specifies virtual device interfaces for sub-systems used in locomotives, power-cars, and coaches. This application profile is part of a virtual multiple network architecture. It is the higher hierarchical virtual network on vehicle sub-level that connects a number of sub-systems. In order to support every physical network architecture, no PDOs have been pre-defined. The virtual interfaces of the sub-system are described in:

• Part 1: General definitions
• Part 2: Train operating system
• Part 3: Monitoring and safety system
• Part 4: Auxiliary operating system
• Part 5: Power (drive) system
• Part 7: Brake control system
• Part 8: Ancillary operating system
• Part 9: Vehicle linkage system
• Part 10: Exterior lighting system
• Part 11: Interior lighting system
• Part 12: Door control system
• Part 13: HVAC system
• Part 18: Slip/slide control system