Z-Wave is a wireless communications protocol designed for home automation, specifically to remotely control applications in residential and light commercial environments. The technology uses a low-power RF radio embedded or retrofitted into home electronics devices and systems, such as lighting, residential access control, entertainment systems and household appliances.
Z-Wave communicates using a low-power wireless technology designed specifically for remote control applications. The Z-Wave wireless protocol is optimized for reliable, low-latency communication of small data packets with data rates up to 100kbit/s, unlike Wi-Fiand other IEEE 802.11-based wireless LAN systems that are designed primarily for high-bandwidth data flow. Z-Wave operates in the sub-gigahertz frequency range, around 900 MHz. This band competes with some cordless telephones and other consumer electronics devices, but avoids interference with Wi-Fi, Bluetooth and other systems that operate on the crowded 2.4 GHz band. Z-Wave is designed to be easily embedded in consumer electronics products, including battery operated devices such as remote controls,smoke alarms and security sensors. Z-Wave was developed by a Danish startup called Zen-Sys that was acquired by Sigma Designs in 2008.

As of 2013, Z-Wave is supported by over 160 manufacturers worldwide and appears in a broad range of consumer and commercial products in the US, Europe and Asia. The lower layers, MAC and PHY, are described by ITU-T G.9959 and fully backwards compatible. The Z-Wave transceiver chips are supplied by Sigma Designs and Mitsumi.
Some Z-Wave product vendors have open source options for the hobbyist communities. They require users to start with a complete Z-Wave transceiver from a Z-Wave OEM such as an Intermatic USB stick. The xPL project also provides open source support for Z-Wave products, but requires Microsoft Windows.
Since 2010, there is a project called Open-zwave that seeks to offer development support without expensive software development kits. Another project has created a Z-Wave daughter board for the Raspberry Pi, a credit-card-sized single-board computer.

Z-Wave is a protocol oriented to the residential control and automation market. Conceptually, Z-Wave is intended to provide a simple yet reliable method to wirelessly control lights and appliances in a house. To meet these design parameters, the Zensys or Sigma Designs Z-Wave package includes a chip with a low data rate that offers reliable data delivery along with simplicity and flexibility.
Z-Wave works in the industrial, scientific, and medical (ISM) band on a single frequency using frequency-shift keying (FSK) radio. The throughput is up to 100 kbit/s (9600 bit/s using older series chips) and suitable for control and sensor applications.
Each Z-Wave network may include up to 232 nodes, and consists of two sets of nodes: controllers and slave devices. Nodes may be configured to retransmit the message in order to guarantee connectivity in the multipath environment of a residential house. Average communication range between two nodes is 30.5 m (100 ft), and with message ability to hop up to four times between nodes, this gives enough coverage for most residential houses.

Radio specifications

Bandwidth: 9.6 or 40 kbit/s, speeds are fully interoperable

Modulation: GFSK Manchester channel encoding

Range: Approximately 100 ft (30 m) assuming "open air" conditions, with reduced range indoors depending on building materials

Frequency band: The Z-Wave Radio uses the 868.42 MHz SRD Band (Europe); the 900 MHz ISM band: 908.42 MHz (United States); 916 MHz (Israel); 919.82 MHz (Hong Kong); 921.42 MHz (Australian/New Zealand).

In Europe, the 868 MHz band has a 1% duty cycle limitation, thus a Z-Wave unit is only allowed to transmit 1% of the time. Z-Wave units can operate in power-save mode and only be active 0.1% of the time, thus reducing power consumption substantially.

Topology and routing

Each Z-Wave network is identified by a Network ID, and each device is further identified by a Node ID.
The Network ID (also called Home ID) is the common identification of all nodes belonging to one logical Z-Wave network. The Network ID has a length of 4 bytes (32 bits) and is assigned to each device, by the primary controller, when the device is "included" into the Network. Nodes with different Network ID’s cannot communicate with each other.
The Node ID is the address of a single node in the network. The Node ID has a length of 1 byte (8 bits). It is not allowed to have two nodes with identical Node ID on a Network.
Z-Wave uses a source-routed mesh network topology, and has one Primary Controller and zero or more Secondary Controllers that control routing and security. Devices can communicate to one another by using intermediate nodes to actively route around and circumvent household obstacles or radio dead spots that might occur. A message from node A to node C can be successfully delivered even if the two nodes are not within range, providing that a third node B can communicate with nodes A and C. If the preferred route is unavailable, the message originator will attempt other routes until a path is found to the C node. Therefore, a Z-Wave network can span much farther than the radio range of a single unit; however, with several of these hops a slight delay may be introduced between the control command and the desired result.
In order for Z-Wave units to be able to route unsolicited messages, they cannot be in sleep mode. Therefore, battery-operated devices are not designed as repeater units. A Z-Wave network can consist of up to 232 devices, with the option of bridging networks if more devices are required.

As a source-routed static network, Z-Wave assumes that all devices in the network remain in their original detected position. Mobile devices, such as remote controls, are therefore excluded from routing.
In later versions of Z-Wave, new network discovery mechanisms were introduced. So-called "explorer frames" can be used to heal broken routes caused by devices that have been moved or removed. Explorer frames are broadcast with a pruning algorithm and are therefore supposed to reach the target device, even without further topology knowledge by the transmitter. Explorer frames are used as a last option by the sending device when all other routing attempts have failed.

(Source: www.wikipedia.org)