This site uses cookies to store information on your computer. Some of these cookies are essential to make our site work and others help us to improve by giving us some insight into how the site is being used. Click to see our cookie policy

close

Partners

Manufacturers

New products

ZigBee FAQ


What is ZigBee? 
What is IEEE802.15.4? 
How is ZigBee different from other wireless standards (e.g. Bluetooth)? 
What are the real-life applications of ZigBee? 
How reliable is the data delivery? 
How long is the battery life? 
What are the cost considerations for ZigBee implementation? 
How long is the Transmisson Range? 
How high is the Data Rate? 
What is the Data Latency for ZigBee Networks? 
How big is a Node? 
How large/small a ZigBee Network can be? 
How is the Data Security provided? 
What is ZigBee Stack? 
What Subunits can be on a Node? 
What is called ZigBee Application? 
What are the ZigBee Device Descriptors? 
hat is ZigBee Device Profile? 
What is ZigBee Stack Profile? 
What are the ZigBee Device Objects? 
How does a Device/Service Discovery process work? 
What are the Clusters, ZigBee Binding and Binding Table? 
How is Addressing and Messaging done in a ZigBee network? 
What types of ZigBee Devices exist in a network? 
What Topologies are supported by ZigBee? 
What is ZigBee network Gateway? 

Take a look at our ranges of ZigBee Modules and Complete ZigBee Solutions

What is ZigBee? 
Top 

ZigBee is an open global standard providing wireless networking based on the IEEE 802.15.4 standard and taking full advantage of a powerful physical radio this standard specifies. ZigBee is the result of collaborative efforts by a global consortium of companies known as the ZigBee Alliance . ZigBee includes the following key features:

Reliability and self-healing 
Support for a large number of nodes 
Fast, easy deployment 
Very long battery life 
Security 
Low cost 
Ability to be used globally 
Product interoperability 
Vendor independence

The term "ZigBee" originates from honeybees' method of communicating newfound food sources. This silent-but-powerful communication system is known as the "ZigBee Principle." By dancing in a zig-zag pattern, the bee is able to share critical information, such as the location, distance, and direction of a newly discovered food source to its fellow hive members.


What is IEEE802.15.4? 
Top 

IEEE 802.15.4 is a standard defined by the IEEE (Institute of Electrical and Electronics Engineers, Inc.) for low-rate, wireless personal area networks (WPANs). This standard defines the "physical layer" and the "medium access layer." The specification for the physical layer, or PHY, defines a low-power spread spectrum radio operating at 2.4 GHz with a basic bit rate of 250 kilobits per second. There are also PHY specifications for 915 MHz and 868 MHz that operate at lower data rates. For more information about IEEE 802.14.5 please refer to the official page .


How is ZigBee different from other wireless standards (e.g. Bluetooth)? 
Top 

There is a multitude of standards that address mid to high data rates for voice, PC LANs, video, etc. However, until ZigBee there hasn't been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and control devices don't need high bandwidth, but they do need low latency and very low energy consumption for long battery lives and for large device arrays.

There are many proprietary wireless systems that function like ZigBee; inexpensive, very-low current draining solutions that address a multitude of problems without requiring high data rates. These proprietary systems were designed because there were no standards that met their requirements. These legacy systems are now creating significant interoperability problems with each other and with newer technologies. 

What are the real-life applications of ZigBee? 
Top 

ZigBee is well suited for a wide range of building automation, industrial, medical and residential control and monitoring applications. Examples include the following: 

Lighting controls 
Automatic Meter Reading 
Wireless smoke and CO detectors 
HVAC control 
Heating control 
Home control, including units such as intrusion sensors, motion detectors, glass break detectors, standing water sensors, loud sound detectors, etc. 

Environmental controls 

Blind, drapery and shade controls 
Medical sensing and monitoring 
Universal Remote Control to a Set-Top Box which includes Home Control 
Industrial and building automation 
Asset management E.g., wireless sensors (temperature, humidity, shock, etc.) are installed into containers, where they form a mesh network. Multiple containers in a ship form a mesh to report sensor data to the ship control center, and further to a port control center. 

How reliable is the data delivery? 
Top 

Reliable data delivery is critical to ZigBee applications. The underlying 802.15.4 standard provides strong reliability through several mechanisms at multiple layers. For example, it uses 27 channels in three separate frequency bands.


The 2.4 GHz band is used worldwide and has 16 channels and a maximum over-the-air data rate of 250 Kbps. Lower frequency bands are also specified. The 902-928 MHz band serves the Americas and much of the Pacific Rim, with 10 channels and a burst rate of 40 Kbps. European applications use one channel in the 868-870 MHz band, which provides 20 Kbps burst rate. This rich assortment of frequencies lets applications with the appropriate hardware configuration adjust in real time to local interference and/or propagation conditions. Once on a specific channel, the 802.15.4 radio relies on a number of mechanisms to ensure reliable data transmission, including binary phase shift keying (BPSK) in the 868/915 MHz bands and offset quadrature phase shift keying (O-QPSK) at 2.4 GHz.

How long is the battery life? 
Top 

The basic 802.15.4 node is fundamentally efficient in terms of battery performance. You can expect battery lifetimes from a few months to many years as a result of a host of system's power-saving modes and battery-optimized network parameters, such as a selection of beacon intervals, guaranteed time slots, and enablement/disablement options. Consider a typical security application, such as a magnetic reed switch door sensor. The sensor itself consumes almost no electricity; it's the radio that uses the bulk of the power. The sensor is configured to have a "heartbeat" at one-minute intervals and to immediately send a message when an event occurs. Assuming dozens of events per day, analysis shows that the sensor can still outlast an alkaline AAA battery. The configuration allows the network to update the sensor parameters remotely, change its reporting interval, or perform other remote functions and still have (theoretical) battery longevity well beyond the shelf life.


What are the cost considerations for ZigBee implementation? 
Top 

System, individual node, service, and battery costs are all important. ZigBee and 802.15.4 maximize utility over this multidimensional space. There is sufficient flexibility in both standards to provide the sensor system developer with an assortment of tradeoffs to optimize cost with respect to system performance. For example, battery life can be optimized at the expense of service interval, and node cost and complexity can be traded for network complexity. System simplicity and the underlying flexibility of 802.15.4 promise that system developers will find ZigBee-based platforms more cost effective (at the same unit volumes) than Bluetooth or proprietary bidirectional wireless solutions. While platform hardware cost is always a critical part of the overall system cost, you must also consider the less tangible costs of system maintenance, flexibility, and battery life.

How long is the Transmission Range? 
Top 

ZigBee relies on the basic 802.15.4 standard to establish radio performance. As a short-range wireless standard, 802.15.4 doesn't try to compete with high-powered transmitters but instead excels in the ultra-long battery life and low transmitter power. The standard specifies transmitter output power at a nominal ?3 dBm (0.5 mW), with the upper limit controlled by the regulatory agencies of the region in which the sensor is used. At ?3 dBm output, single-hop ranges of 10 to more than 100 m are reasonable, depending on the environment, antenna, and operating frequency band. Instead of pure power, ZigBee augments the basic 802.15.4 simple transmitter and protocol with an extensible, sophisticated network function that allows multi-hop and flexible routing, providing communication ranges that can exceed the basic single-hop. Indeed, depending on the data latency requirements, you can practically create networks that use dozens of hops, with cumulative ranges in the hundreds to thousands of meters. Networks can have star, cluster tree, or mesh structures; each comes with its own strengths.

How high is the Data Rate? 
Top 

It may not be obvious why a simple temperature or intrusion sensor needs to transmit data at 250 Kbps (at 2.4 GHz) or even 20 Kbps (at 868 MHz), but the reason becomes clear when you consider the need to prolong battery life. Even when the sensor is transmitting only a few bits or bytes, the system can be more efficient if it transmits and receives the data quickly. For instance, a 0.5 mW transmitter consumes many milliwatts whether it's transmitting 100 or 100,000 bps. For any given quantity of data, transmitting at a higher data rate allows the system to shut down the transmitter and receiver more quickly, saving significant power. Higher data rates at a given power level mean there's less energy per transmitted bit, which generally implies reduced range. But both 802.15.4 and ZigBee value battery life more than raw range and provide mechanisms to improve range while always concentrating on battery life.

What is the Data Latency for ZigBee Networks?
Top 

Sensor systems have a broad range of data-latency requirements. If sensor data are needed within tens of milliseconds, as opposed to dozens of seconds, the requirement places different demands on the type and extent of the intervening network. For many sensor applications, data latency is less critical than battery life or data reliability. For simple star networks (many clients, one network coordinator), ZigBee can provide latencies as low as ~16 ms in a beacon-centric network, using guaranteed time slots to prevent interference from other sensors. You can further reduce latencies by several milliseconds if you forego the beacon environment and are willing to risk potential interference from accidental data collision with other sensors on the network. Data latency can also affect battery life. Generally, if you relax data-latency requirements, you can assume that the battery life of the client nodes will increase. This is even truer of network hubs, which are required to coordinate and supervise the network. 

How big is a Node? 
Top 

As silicon processes and radio technology progress, transceiver systems shrink in physical size. Forty years ago, a simple radio transceiver was the size of a shoebox and weighed 10 kg. Today, a similar transceiver might easily fit inside a thimble. In the case of ZigBee systems, the radio transceiver has become a single piece of silicon, with a few passive components and a relatively non-critical board design. Microcontrollers that have native ability to interface with sensors (e.g., built-in digital I/O and A/D converters) have eclipsed even the radio's rapid reduction in size. Today, the 8-bit MCU that hosts the application may already include dozens of kilobytes of flash memory, RAM, and various hardware-based timer functions, along with the ability to interface directly to the radio transceiver IC. The MCU requires only a few external passive components to be fully functional. With the minimal overhead added by a ZigBee transceiver, the MCU can often continue to host the application along with the ZigBee protocol. Therefore, the silicon system size of a ZigBee solution (excluding sensors or batteries) is generally smaller than the batteries themselves. This compact form factor lends itself well to innovative uses of radio technology in sensor applications. Certainly, with the advances in silicon-based sensors that have been coming to market over the past five years, it's practical to design entire systems that take up less than 10-20% of the volume of current-generation batteries. Integration is the key here, and even higher levels of integration are planned for future ZigBee and 802.15.4 platforms.

How large/small a ZigBee Network can be? 
Top 

The addressing space allows of extreme node density-up to 18,450,000,000,000,000,000 (264) devices (64 bit IEEE address), which may form different topologies depending on customer needs: star, mesh, cluster tree. At the same time, using local addressing, simple networks of more than 65,000 (2^16) nodes can be configured, with reduced address overhead.

How is the Data Security provided? 
Top 

It's important to provide your sensor network with adequate security to prevent the data from being compromised, stolen, or tampered with. IEEE 802.15.4 provides authentication, encryption, and integrity services for wireless systems that allow systems developers to apply security levels as required. These include no security, access control lists, and 32-bit to 128-bit AES encryption with authentication. This security suite lets the developer pick and choose the security necessary for the application, providing a manageable tradeoff against data volume, battery life, and system processing power requirements. The IEEE 802.15.4 standard doesn't provide a mechanism for moving security keys around a network; this is where ZigBee comes in. The ZigBee security toolbox consists of key management features that let you safely manage a network remotely. For those systems where data security is not critical (e.g., a set of sensors monitoring microclimates in a forest), you may decide not to implement security features but instead optimize battery life and reduce system cost. For the developer of an industrial or military perimeter security sensor system, data security-and more importantly the ability to defend against sensor masking or spoofing-may have the higher priority. In many ZigBee-approved applications, security will already be a seamless part of the overall system.

What is ZigBee Stack? 
Top 

ZigBee is based upon stack architecture that resembles standard OSI seven-layer model but defines only those layers relevant to achieving functionality in the intended scope.

ZigBee Stack Architecture

The ZigBee stack architecture is made up of a set of blocks called layers. Each layer performs a specific set of services for the layer above: a data entity provides a data transmission service and a management entity provides all other services. Each service entity exposes an interface to the upper layer through a service access point (SAP), and each SAP supports a number of service primitives to achieve the required functionality. IEEE 802.15.4 standard defines the lower two layers: the physical (PHY) layer and the medium access control (MAC) sub-layer. The ZigBee Alliance builds on this foundation by providing the network (NWK) layer and the framework for the application layer, which includes the application support (APS) sub-layer, the ZigBee device object (ZDO) and the manufacturer-defined application objects. IEEE 802.15.4 has two PHY layers that operate in two separate frequency ranges: 868/915 MHz and 2.4 GHz. The lower frequency PHY layer covers both the 868 MHz European band and the 915 MHz band that is used in countries such as the United States and Australia. The higher frequency PHY layer is used virtually worldwide. The IEEE 802.15.4 MAC sub-layer controls access to the radio channel using a CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism. Its responsibilities may also include transmitting beacon frames, synchronization and providing a reliable transmission mechanism. The responsibilities of the ZigBee NWK layer include mechanisms used to join and leave a network, to apply security to frames and to route frames to their intended destinations. In addition, the discovery and maintenance of routes between devices devolve to the NWK layer. Also the discovery of one-hop neighbours and the storing of pertinent neighbour information are performed by the NWK layer. The NWK layer of a ZigBee coordinator is responsible for starting a new network, when appropriate, and assigning addresses to newly associated devices. For more information about the NWK layer please refer to 02130r10ZB_NWK_Network-Specification_V100 document of ZigBee specification v.1.0. The ZigBee application layer consists of the APS sub-layer, the ZDO (containing the ZDO management plane), and the manufacturer-defined application objects. The responsibilities of the APS sub-layer include maintaining tables for binding, which is the ability to match two devices together based on their services and their needs, and forwarding messages between bound devices. The responsibilities of the ZDO include defining the role of the device within the network (e.g., ZigBee coordinator or end device), discovering devices on the network and determining which application services they provide, initiating and/or responding to binding requests and establishing a secure relationship between network devices. The ZigBee stack is small in comparison to other wireless standards. For network-edge devices with limited capabilities, the stack requires about 4Kb of the memory. Full implementation of the protocol stack takes less than 32Kb of memory. The network coordinator may require extra RAM for a node devices database and for transaction and pairing tables.

What Subunits can be on a Node? 
Top 

ZigBee network consists of a number of ZigBee Devices or Nodes. A node is a piece of hardware that shares a single radio. Nodes can have several subunits, which are physical devices: sensors, switches, lamps etc. Node subunits are modeled with Application Objects (AOs). In other words, Application Object is a program that controls hardware device. ZigBee does not specify internal structure of this program. The maximum number of subunits per node is 240. Each subunit is assigned an endpoint number, which is used to identify it. Thus, each identifiable subunit in a node is assigned its own specific endpoint in the range 1-240. In the figure below, there are two nodes, each containing a single radio. One node contains two switches and the other contains 4 lamps.

What is called ZigBee Application? 
Top 

ZigBee Application is a group of Application Objects located on the same and/or different Nodes. For example, a lighting control application may consist of light sensors, light switches, light controllers, and lamps Application Objects. To run a few steps forward, it's worthwhile to note that Application is an implementation of an Application Profile (please see ZigBee Profiles section of this document). For details, please address section 3.2 of 03525r6ZB_AFG_Application-Framework_V100 ZigBee specification v.1.0 document.

What are the ZigBee Device Descriptors? 
Top 

Every subunit and thus Application Object has associated Device Descriptors such as Simple Descriptor. Device Descriptors contain data attributes (both input and output) that describe physical device. For instance, a thermostat might contain an output attribute "temperature" which represents the current temperature of a room. A furnace controller may take this attribute as an input and control the furnace according to the temperature value received from the thermostat. Valid values, ranges, and units for the attributes are included as well. The important thing is that a Device Descriptor is specific to the application working with this device. In other words, Device Descriptor is an "application view" of some device at some ZigBee Node. Different applications may have different views of one and the same device, thus a single device may have several distinct Device Descriptors.

There are five types of Descriptors specified by ZigBee: 

Node - specifies type and capabilities of the node/LI> 
Node power - gives a dynamic indication of the power status of the node. 
Simple - contains information specific to each endpoint contained in this node. 
Complex (optional) - contains extended information for each of the device descriptions contained in this node. 
User (optional) - contains information that allows the user to identify the device using a user-friendly character string, such as "Bedroom TV" or "Stairs light." 

What is ZigBee Device Profile? 
Top 

A set of Device Descriptors that describes a distributed "application view" of several devices is called ZigBee Device Profile (also referred to as Application Profile or simply Profile). Thus, in ZigBee there's one-to-one correspondence of Application Profiles and Applications. Profiles are developed by ZigBee vendors to address solutions to specific technology needs. Profiles are simultaneously a means to unify interoperable technical solutions within the ZigBee standard, as well as to focus usability efforts within a given marketing area. For example, it is expected that vendors of lighting equipment will want to provide ZigBee profiles that interoperate with several varieties of lighting types or controller types. Application Profile is not an entity or some kind of software, but rather an agreement on messages, message formats and processing actions that enable applications residing on separate devices to send commands, request data and process commands/requests to create an interoperable, distributed application. The figure below shows a graphical representation of a part of Home Control Lightning (HCL) profile developed by ZigBee Alliance for home lightning management.

There are Switch, Remote Control, Occupancy Sensor, and Switching Load Controller depicted (other devices are missing here). Attributes at the left side of devices are input attributes; at the right, output attributes. As shown, the output on/off attribute for the Switch Remote Control is the input for the Switching Load Controller.

What is ZigBee Stack Profile? 
Top 

Stack Profiles are a convention on specific ZigBee Protocol Stack Settable Values established to provide interoperability in specified markets. Stack Settable Values are settings that need to be chosen so that differing ZigBee implementations and networks will be able to interoperate. The following stack profiles have been identified for ZigBee v1.0: 

Home Controls - intended for use with the Home Controls-Lighting application profile and all profiles written for complementary use with Home Controls-Lighting. 
Building Automation - intended for use with future profiles targeted to building automation solutions. 
Plant Control - intended for use with future profiles targeted to plant control solutions. Additionally, a category of stack profile called "Network Specific" is proposed which indicates that no specific Stack Profile is in use; rather, the stack parameters are defined by the elemental values employed as stack parameters.

What are the ZigBee Device Objects? 
Top 

ZigBee Device Objects (ZDO) are an application solution residing within the Application Layer (APL) and above the Application Support Sub-layer (APS) in the ZigBee stack architecture. ZDO are responsible for defining the role of devices within the network (e.g., ZigBee coordinator or end device), discovering devices on the network and determining which application services they provide, initiating and/or responding to binding requests and establishing a secure relationship between network devices. From Application point of view, ZDO is an interface to the ZigBee stack (together with the Application Support Sub-layer).

How does a Device/Service Discovery process work? 
Top 

Device discovery is the process whereby a ZigBee device can discover other ZigBee devices by initiating queries that are broadcast or unicast addressed. Service discovery is the process whereby services available on endpoints at the receiving device are discovered by external devices. Service means the interfaces described by means of Device Descriptors set. Service discovery can be accomplished by issuing a query for each endpoint on a given device, by using a match service feature (either broadcast or unicast) or by having devices announce themselves when they join the network. Service discovery utilizes the complex, user, node or power descriptors plus the simple descriptor further addressed by the endpoint (for the connected application object). The service discovery process in ZigBee is critical for successfully interfacing devices within the network. Through specific requests for descriptors on specified nodes, broadcast requests for service matching and the ability to ask a device which endpoints support application objects, a range of options are available for commissioning tools and applications.

What are the Clusters, ZigBee Binding and Binding Table? 
Top 

A group of a number of Attributes (more or equal to one) is referred to as Cluster. Each Cluster has a unique ID in the scope of a Profile. Cluster identifiers participate in Binding. Binding is a point-to-point logical link between Input/Output ClusterIDs belonging to one Application Object and Input/Output ClusterIDs of another Application Object. The information about which Cluster is bound between Nodes is stored in a Binding Table. The example below clarifies the binding concept.

The use of a list of three entries in the binding table for switch 1 allows it to control three lamps, which could also be in separate nodes (with their own ZigBee radios). It is also possible for one lamp to be controlled by several switches: in this case there would be entries for each switch, all linked to the same lamp.

How is Addressing and Messaging done in a ZigBee network? 
Top 

Each Node has a unique IEEE and NWK (ZigBee Network Layer) address that is assigned when a node joins the network. Every subunit and thus Application Object in a node is addressed by endpoint number unique within a node. An Application Object receives commands from outside world addressed to pair: (node address, endpoint number). AO commands may be of two types: Key-Value Pair (KVP) and Generic Messages.

What types of ZigBee Devices exist in a network? 
Top 

According to IEEE MAC specification that introduces three device types, ZigBee specifies the following ZigBee Devices: 

ZigBee Coordinator (MAC Network Coordinator). Maintains overall network knowledge; most sophisticated of the three types; most memory and computing power 
ZigBee Router (MAC Full Function Device: Carries full 802.15.4 functionality and all features specified by the standard). 
ZigBee End Device (MAC Reduced Function Device: Carriers limited functionality to control cost and complexity. Also, may be MAC Full Function Device). That's where the physical devices reside. 

What Topologies are supported by ZigBee? 
Top 

The figure below illustrates the possible network configurations and the roles of the devices.

As shown above, there are three different network topologies that are supported by Zigbee, namely the star, mesh and cluster tree or hybrid networks. Each has its own advantages and can be used to advantage in different situations. The star network is commonly used, having the advantage of simplicity. As the name suggests it is formed in a star configuration with outlying nodes communicating with a central node. Mesh or peer-to-peer networks enable high degrees of reliability. They consist of a variety of nodes placed as needed, and nodes within range being able to communicate with each other to form a mesh. Messages may be routed across the network using the different stations as relays. There is usually a choice of routes that can be used and this makes the network very robust. If interference is present on one section of a network, then another can be used instead. Finally there is what is known as a cluster tree network. This is essentially a combination of star and mesh topologies.

What is ZigBee network Gateway? 
Top 

There is another important type of ZigBee Node: Gateway. Its responsibilities are to interface a ZigBee network into an external system, and to provide inter-network communications. Gateways clear the way for ZigBee integration with existing and co-existing systems, for arrangement a global network that unites a number of underlying ZigBee networks as well as other solutions and information systems. ZigBee Gateway is intended to provide an interface between ZigBee and IP devices through an abstracted interface on the IP side. The IP device is isolated from the ZigBee protocol by that interface. The ZigBee Gateway translates both addresses and commands between ZigBee and IP.