SAE J2355_199710

This SAE Information Report describes a reference model for an in-vehicle data bus for Intelligent Transportation Systems (ITS). It introduces the ITS Data Bus (IDB) reference model and describes overall IDB concepts. Vehicle OEMs would like to be able to offer state of the art entertainment, traveler information, communications and security devices (modules) to their customers, but are hampered by the current design cycle of new vehicles. OEM and third party electronics companies would like to be able to design automotive electronics for use across multiple vehicle platforms and across vehicle manufacturers, but there is currently no single standard interface. Drivers would like to be able to install a variety of state of the art electronics devices in their vehicles even after purchase, but installation can be complicated and expensive, and rarely results in integrated systems. Most modern computing paradigms embrace the concepts of network and distributed computing. It is natural therefore to consider these concepts as one addresses the requirements of the vehicle. Although vehicle manufacturers are indeed using multiplex buses (the automotive equivalent of a local area network), there remain a number of problems. For a variety of reasons vehicle companies are not converging on a single standard. As a result, device manufacturers must design and build multiple versions of their products to attach to the various buses, raising the cost. A device (electronic module) connected to the vehicle's multiplex bus must be qualified through the normal design cycle of the vehicle, which does not easily allow unplanned-for electronics to be added by the manufacturer, the dealer, or the customer. For warranty, safety, and liability reasons, electronic devices must not be allowed to interfere in any way with the operation of the vehicle or of any of its subsystems, so they cannot be easily retrofitted to the vehicle's multiplex bus. A dual-bus architecture is proposed as the basis for a family of SAE standards, in which an IDB is connected to the vehicle's multiplex bus through a gateway. This allows electronic device manufacturers to build a single, automotive version of their product that plugs into the IDB on any vehicle. In addition, the IDB is independent of all vehicle systems, except for power, eliminating the need for a full electrical bench qualification (of course, maximum power drain in ignition-on and ignition-off states will have to be specified and EMC specifications will have to be met by IDB devices). The gateway, under control of the vehicle company, acts as a "firewall", allowing only authorized message traffic to pass between the vehicle's multiplex bus and the IDB devices. This "firewall" has significant safety benefits, as it prevents ITS bus message traffic from interfering with basic functions of the vehicle.