This part of ISO/IEC 14543 specifies a wireless protocol for low-powered devices such as energy harvested devices in a home environment. This wireless protocol is specifically designed to keep the energy consumption of such sensors and switches extremely low. The design is characterised by • keeping the communications very short, infrequent and mostly unidirectional, and • using communication frequencies that provide a good range even at low transmit power and avoid collisions from disturbers. This allows the use of small and low cost energy harvesters that can compete with similar batteries-powered devices. The messages sent by energy harvested devices are received and processed mainly by line-powered devices such as relay switch actuators, repeaters or gateways. Together these form part of a home automation system, which, when conforming to the ISO/IEC 14543 series of standards, is defined as a home electronic system. This part of ISO/IEC 14543 specifies OSI Layers 1 to 3 of the Wireless Short-Packet (WSP) protocol. The WSP protocol system consists of two and optionally three types of components that are specified in this standard. These are the transmitter, the receiver and optionally the repeater. Repeaters are needed when the transmitter and the receiver are located in such a way that no good direct communication between them can be established. Protection against malicious attacks is handled in the upper layers and thus not treated in this standard.