J1939-based higher-layer protocols derive from the SAE J1939 series of specifications. These specifications have been originally developed for diesel engines used in trucks and buses. In the meantime, some derivate have been developed for special purposes. This includes the ISO 11783 series (also known as Isobus) for agriculture and forestry machines, and the IEC 61162-3 (also known as Nema 2000) for marine navigation systems. The ISO 11992 standard for truck/trailer communications is also based on J1939.