This document defines the cabling specifications for an onboard data transmission bus between the different parts of equipment for service operations and monitoring of the fleet. This document is applicable to equipment installed onboard buses, trolley buses and tramways only as part of a bus fleet operation. This equipment include operations aid systems, automatic passenger information systems, fare collection systems, etc. Equipment directly related to the functioning of the vehicle (e.g. driver dashboard, engine management, brake systems, door opening systems) are excluded from the scope of this document and are dealt with in other standardisation bodies