This Technical Specification specifies the choice and the general application's rules of an onboard data transmission bus between the different equipment for service operations and monitoring of the fleet. This applies to equipment installed onboard buses, trolley-buses and tramways only as part of a bus fleet operation. It excludes tramways when they are operated as part of a train, subway or metro operation. This equipment includes operation aid systems, automatic passenger information systems, fare collection systems, etc. The 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 the present standard and are dealt with in other standardisation bodies.