ZigBee refers to a suite of high level communication protocols using small, low power devices based on IEEE 802.15.4 standard for wireless personal area networks.This technology is simpler and cheaper than any other WPANs. ZigBee is targeted at Radio Frequency applications that require a low data rate , low power usage, and secure networking. 802.15.4 defines the physical layer, and ZigBee defines the network and application layers. In other words ZigBee is a low cost, low power , wireless mesh networking standard. The low cost allows the technology to be widely accepted and deployed in wireless control and monitoring applications, the low power usage allows longer life with smaller batteries and mesh networking provides high reliability and larger range. The relationship between IEEE 802.15.4-2003 and ZigBee is similar to that between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specification was ratified on December 14, 2004.
Applications
The self configuring and self healing capabilities of the ZigBee makes it employable in many of the day to day applications. Various applications include. 1) Energy management applications
2) Home Automation
3) Building Automation
4) Industrial Automation
5) Telecommunication and applications
6) Hospital care
7) Mobile Services
Advantages
Advantages of ZigBee are
1) low Cost
2) Secure
3) Reliable and self healing
4) Flexible and extendable
5) Low power consumption
6) Easy and inexpensive to deploy
ZigBee is the only standards-based technology that addresses the unique needs of most remote monitoring and control sensory network applications.
ZigBee Alliance
The ZigBee Alliance is an association of over 285 companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard. Their focus is on the following:
• Defining the network, security and application software layers
• Providing interoperability and conformance testing specifications
• Promoting the ZigBee brand globally to build market awareness
• Managing the evolution of the technology
The Zig Bee Protocol Stack
Application layer- The top layer in Zigbee protocol stack consists of the Application Framework, ZigBee Device Object and Application support sublayer.
Application frame work- It provides a description of how to build a profile on to ZigBee stack
Application objects- Software at an endpoint that controls the ZigBee device.
ZigBee Device object- Defines the role of a device within the network , initiates and responds to binding and discovery requests, and establishes a secure relationship between network devices. It also provides a rich set of management commands defined in the ZigBee Device Profile . The ZDO is always endpoint zero.
Application Support Sublayer- Responsible for providing a data service to the application and ZigBee device profiles. It also provides a management service to maintain binding links and the storage of the binding table itself.
Security Service Provider- Provides security mechanisms for layers that use encryption (NWK and APS). Initialized and configured through the ZDO.
Network Layer- Handles network address and routing by invoking actions in the MAC layer. Its tasks include starting the network (coordinator), assigning network addresses, adding and removing network devices, routing messages, applying security, and implementing route discovery.
ZigBee Device types
ZigBee networks include the following device types:
• Coordinators
• Routers
• End devices
Coordinator
This device starts and controls the network. The coordinator stores information about the network, which includes acting as the Trust Center and being the repository for security keys.
Router
These devices extend network area coverage, dynamically route around obstacles, and provide backup routes in case of network congestion or device failure. They can connect to the coordinator and other routers, and also support child devices.
End Devices
These devices can transmit or receive a message, but cannot perform any routing operations. They must be connected to either the coordinator or a router, and do not support child devices.
ZigBee protocols
In most large network instances, the network will be a cluster of clusters. It can also form a mesh or a single cluster. The current profiles derived from the ZigBee protocols support beacon and non-beacon enabled networks. In non-beacon-enabled networks (those whose beacon order is 15), an unslotted CSMA/CA channel access mechanism is used. In this type of network, ZigBee Routers typically have their receivers continuously acIn beacon-enabled networks, the special network nodes called ZigBee Routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus lowering their duty cycle and extending their battery life.tive, requiring a more robust power supply. 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. The radios use direct-sequence spread spectrum coding, which is managed by the digital stream into the modulator. BPSK is used in the 868 and 915 MHz bands, and orthogonal QPSK that transmits two bits per symbol is used in the 2.4 GHz band.
Disclaimer-
ZigBee® is a registered trademark of the ZigBee Alliance.
802.15.4™ is a trademark of the Institute of Electrical and Electronics Engineers (IEEE).
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