SAE J1939-01 On-Highway Equipment Control and Communication Network specifies the minimum set of SAE J1939 documents that define the Truck and Bus Control and Communications Vehicle Network as it applies to on-highway equipment. Vehicles covered include all on-highway straight trucks and road trains. A road train consists of one towing vehicle (tractor) and one or more towed vehicles (trailers and dollies). Dolly axles within the road train are considered to be towed vehicles. Purpose It is the intention of the SAE J1939 family of recommended practices to allow electronic devices to communicate with each other by providing a standard architecture. SAE J1939-01 describes the particular set of SAE J1939 documents used to implement an open interconnect system for electronic systems in a heavy-duty on-highway vehicle. Vehicles covered include on-highway straight trucks and combination vehicles. A combination vehicle consists of one towing vehicle (tractor)@ and one or more towed vehicle(s) (trailers and dollies). Dolly axles within the combination vehicle are considered to be towed vehicles. Degrees of Openness A network based upon this document is open to the degree that any two devices which conform to SAE J1939-01 can be connected via the network and communicate with each other without functional interference. Devices that conform to different SAE J1939-0x documents may not be capable of communicating directly with one another and in some cases may cause degradation or complete disruption of the entire network.