This Technical Specification specifies the physical layer of an onboard data transmission bus between the different equipment for service operations and monitoring of the fleet. This applies to equipment installed on board vehicles that are operating as part of a public transport network, i.e. in operation under public service contracts. This equipment includes operation aid systems, automatic passenger information systems, fare collection systems, etc.Equipment directly related to the safety-related functioning of the vehicle (propulsion management, brake systems, door opening systems, etc...) are excluded from the scope of this Technical Specification and are dealt with in other standardization bodies. Interfaces to such equipment or safety-critical networks can be provided through dedicated gateways.Part 8 covers the link between equipment inside vehicles consisting of one carriage only, e.g. buses and trolleybuses, as well as a set of carriages, e.g. trams and trains.For the described application, three communication systems are standardised under EN 13149. There is no ranking between the three communication systems.— Parts 1, 2 and 3 describe the WORLDFIP communication system;— Parts 4, 5 and 6 describe the CANopen communication system;— Parts 7, 8 and 9 describe the IP-based communication system.