Zigbee


Zigbee is an IEEE 802.15.4-based specification for a suite of high-level communication protocols used to create personal area networks with small, low-power digital radios, such as for home automation, medical device data collection, and other low-power low-bandwidth needs, designed for small scale projects which need wireless connection. Hence, Zigbee is a low-power, low-data-rate, and close-proximity wireless ad hoc network.
The technology defined by the Zigbee specification is intended to be simpler and less expensive than other wireless personal area networks, such as Bluetooth or more general wireless networking such as Wi-Fi. Applications include wireless light switches, home energy monitors, traffic management systems, and other consumer and industrial equipment that requires short-range low-rate wireless data transfer.
Its low power consumption limits transmission distances to line-of-sight, depending on power output and environmental characteristics. Zigbee devices can transmit data over long distances by passing data through a mesh network of intermediate devices to reach more distant ones. Zigbee is typically used in low data rate applications that require long battery life and secure networking. Zigbee has a defined rate of up to, best suited for intermittent data transmissions from a sensor or input device.
Zigbee was conceived in 1998, standardized in 2003, and revised in 2006. The name refers to the waggle dance of honey bees after their return to the beehive.

Overview

Zigbee is a low-power wireless mesh network standard delivering low-latency communication, and targeted at battery-powered devices in wireless control and monitoring applications. Zigbee chips are typically integrated with radios and with microcontrollers.
Zigbee operates in the industrial, scientific and medical radio bands, with the band being primarily used for lighting and home automation devices in most jurisdictions worldwide. Devices for commercial utility metering and medical device data collection often use sub-GHz frequencies: 902-928 MHz in North America, Australia, and Israel, 868-870 MHz in Europe, 779-787 MHz in China. Data rates vary from around for sub-GHz bands to around for the 2.4 GHz band.
Zigbee builds on the physical layer and media access control defined in the IEEE 802.15.4 standard for low-rate wireless personal area networks. The Zigbee specification includes four additional key components: network layer, application layer, and manufacturer-defined application objects. ZDOs are responsible for tasks including keeping track of device roles, managing requests to join a network, and discovering and securing devices.
The Zigbee network layer natively supports star and tree, and generic mesh networking topologies. Every network must have one coordinator device. Within star networks, the coordinator must be the central node. Both trees and meshes allow the use of Zigbee routers to extend communication at the network layer. Another defining feature of Zigbee is facilities for carrying out secure communications, protecting the establishment and transport of cryptographic keys, ciphering frames, and controlling devices. For this, it builds on the basic security framework defined in IEEE 802.15.4.

History

Zigbee-style self-organizing ad hoc digital radio networks were conceived in the 1990s. The IEEE 802.15.4-2003 Zigbee specification was ratified on December 14, 2004. The Connectivity Standards Alliance announced availability of Specification 1.0 on June 13, 2005, known as the ZigBee 2004 Specification.

Cluster library

In September 2006, the Zigbee 2006 Specification was announced, obsoleting the 2004 stack The 2006 specification replaces the message and key–value pair structure used in the 2004 stack with a cluster library. The library is a set of standardised commands, attributes and global artifacts organised under groups known as clusters with names such as Smart Energy, Home Automation, and .
In January 2017, Connectivity Standards Alliance renamed the library to Dotdot and announced it as a new protocol to be represented by an emoticon . They also announced it will now additionally run over other network types using Internet Protocol and will interconnect with other standards such as Thread. Since its unveiling, Dotdot has functioned as the default application layer for almost all Zigbee devices.

Zigbee Pro

Zigbee Pro, also known as Zigbee 2007, was finalized in 2007. A Zigbee Pro device may join and operate on a legacy Zigbee network and vice versa. Due to differences in routing options, a Zigbee Pro device must become a non-routing Zigbee End Device on a legacy Zigbee network, and a legacy Zigbee device must become a ZED on a Zigbee Pro network. It operates using the 2.4 GHz ISM band, and adds a sub-GHz band.

Use cases

Zigbee protocols are intended for embedded applications requiring low power consumption and tolerating low data rates. The resulting network will use very little power—individual devices must have a battery life of at least two years to pass certification.
Typical application areas include:
Zigbee is not for situations with high mobility among nodes. Hence, it is not suitable for tactical ad hoc radio networks in the battlefield, where high data rate and high mobility is present and needed.

Application profiles

The first Zigbee application profile, Home Automation, was announced November 2, 2007. Additional application profiles have since been published.
The specifications define an Internet Protocol-based communication protocol to monitor, control, inform, and automate the delivery and use of energy and water. It is an enhancement of the Zigbee Smart Energy version 1 specifications. It adds services for plug-in electric vehicle charging, installation, configuration and firmware download, prepay services, user information and messaging, load control, demand response and common information and application profile interfaces for wired and wireless networks. It is being developed by partners including:
Zigbee Smart Energy relies on Zigbee IP, a network layer that routes standard IPv6 traffic over IEEE 802.15.4 using 6LoWPAN header compression.
In 2009, the Radio Frequency for Consumer Electronics Consortium and Connectivity Standards Alliance agreed to jointly deliver a standard for radio frequency remote controls. Zigbee RF4CE is designed for a broad range of consumer electronics products, such as TVs and set-top boxes. It promised many advantages over existing remote control solutions, including richer communication and increased reliability, enhanced features and flexibility, interoperability, and no line-of-sight barrier. The Zigbee RF4CE specification uses a subset of Zigbee functionality allowing to run on smaller memory configurations in lower-cost devices, such as remote control of consumer electronics.

Radio hardware

The radio design used by Zigbee has few analog stages and uses digital circuits wherever possible. Products that integrate the radio and microcontroller into a single module are available.
The Zigbee qualification process involves a full validation of the requirements of the physical layer. All radios derived from the same validated semiconductor mask set would enjoy the same RF characteristics. Zigbee radios have very tight constraints on power and bandwidth. An uncertified physical layer that malfunctions can increase the power consumption of other devices on a Zigbee network. Thus, radios are tested with guidance given by Clause 6 of the 802.15.4-2006 Standard.
This standard specifies operation in the unlicensed 2.4 to 2.4835 GHz, 902 to 928 MHz and 868 to 868.6 MHz ISM bands. Sixteen channels are allocated in the 2.4 GHz band, spaced 5 MHz apart, though using only 2 MHz of bandwidth each. The radios use direct-sequence spread spectrum coding, which is managed by the digital stream into the modulator. Binary phase-shift keying is used in the 868 and 915 MHz bands, and offset quadrature phase-shift keying that transmits two bits per symbol is used in the 2.4 GHz band.
The raw, over-the-air data rate is per channel in the 2.4 GHz band, per channel in the 915 MHz band, and in the 868 MHz band. The actual data throughput will be less than the maximum specified bit rate because of the packet overhead and processing delays. For indoor applications at 2.4 GHz transmission distance is 10–20 m, depending on the construction materials, the number of walls to be penetrated and the output power permitted in that geographical location. The output power of the radios is generally 0–20 dBm.

Device types and operating modes

There are three classes of Zigbee devices:
  • Zigbee coordinator : The most capable device, the coordinator forms the root of the network tree and may bridge to other networks. There is precisely one Zigbee coordinator in each network since it is the device that started the network originally. It stores information about the network, including acting as the trust center and repository for security keys.
  • Zigbee router : As well as running an application function, router devices can act as intermediate routers, passing data on to other devices. These types of Zigbee products are typically mains-powered so they are always available on the network. Zigbee Router devices are sometimes called Zigbee repeaters or Zigbee range extenders.
  • Zigbee end device : Contains just enough functionality to talk to the parent node ; it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time, thereby giving long battery life. These types of Zigbee device products are often battery-powered. A ZED requires the least amount of memory and thus can be less expensive to manufacture than a ZR or ZC.
The current Zigbee protocols support beacon-enabled and non-beacon-enabled networks.
In non-beacon-enabled networks, an unslotted CSMA/CA channel access mechanism is used. In this type of network, Zigbee routers typically have their receivers continuously active, requiring additional power. However, this allows for heterogeneous networks in which some devices receive continuously while others transmit when necessary. The typical example of a heterogeneous network is a wireless light switch: The Zigbee node at the lamp may constantly receive since it is reliably powered by the mains supply to the lamp, while a battery-powered light switch would remain asleep until the switch is thrown. In this case, the switch wakes up, sends a command to the lamp, receives an acknowledgment, and returns to sleep. In such a network, the lamp node will be at least a Zigbee router, if not the Zigbee coordinator; the switch node is typically a Zigbee end device.
In beacon-enabled networks, Zigbee routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus extending their battery life. Beacon intervals depend on data rate; they may range from 15.36 milliseconds to 251.65824 seconds at, from 24 milliseconds to 393.216 seconds at and from 48 milliseconds to 786.432 seconds at. Long beacon intervals require precise timing, which can be expensive to implement in low-cost products.
In general, the Zigbee protocols minimize the time the radio is on, so as to reduce power use. In beaconing networks, nodes only need to be active while a beacon is being transmitted. In non-beacon-enabled networks, power consumption is decidedly asymmetrical: Some devices are always active while others spend most of their time sleeping.
Except for Smart Energy Profile 2.0, Zigbee devices are required to conform to the IEEE 802.15.4-2003 Low-rate Wireless Personal Area Network standard. The standard specifies the lower protocol layers—the physical layer, and the media access control portion of the data link layer. The basic channel access mode is carrier-sense multiple access with collision avoidance. That is, the nodes communicate in a way somewhat analogous to how humans converse: a node briefly checks to see that other nodes are not talking before it starts. CSMA/CA is not used in three notable exceptions:
  • Message acknowledgments.
  • Beacons are sent on a fixed-timing schedule.
  • Devices in beacon-enabled networks that have low-latency, real-time requirements may also use guaranteed time slots.