ISO 11783 as a whole specifies a serial data network for control and communications on forestry or agricultural tractors and mounted, semi‑mounted, towed or self-propelled implements. Its purpose is to standardize the method and format of transfer of data between sensor, actuators, control elements and information storage and display units, whether mounted on, or part of, the tractor or implement. ISO 11783-4:2011 describes the network layer, which defines the requirements and services needed for communication between control functions (CFs) in different segments of the ISO 11783 network. The various types of network interconnection units are defined in ISO 11783-4:2011.