Up till now there hasn't been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and controls 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.
ZigBee Technology: Wireless Control that Simply Works
Why is ZigBee needed?
There are a multitude of standards like Bluetooth and WiFi that address mid to high data rates for voice, PC LANs, video, etc. However, up till now there hasn't been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and controls 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 a multitude of proprietary wireless systems manufactured today to solve a multitude of problems that don't require high data rates but do require low cost and very low current drain. These proprietary systems were designed because there were no standards that met their application requirements. These legacy systems are creating significant interoperability problems with each other and with newer technologies.
The ZigBee Alliance is not pushing a technology; rather it is providing a standardized base set of solutions for sensor and control systems.
ZigBee is poised to become the global control/sensor network standard. It has been designed to provide the following features:
ZigBee/IEEE 802.15.4 - General Characteristics
ZigBee/IEEE802.15.4 - Typical Traffic Types Addressed
Each of these traffic types mandates different attributes from the MAC. The IEEE802.15.4 MAC is flexible enough to handle each of these types.
The IEEE 802.15.4 PHY and MAC along with ZigBee's Network and Application Support Layer provide:
There are two physical device types for the lowest system cost. The IEEE standard defines two types of devices:
An IEEE 802.15.4/ZigBee network requires at least one full function device as a network coordinator, but endpoint devices may be reduced functionality devices to reduce system cost.
When security of MAC layer frames is desired, ZigBee uses MAC layer security to secure MAC command, beacon, and acknowledgement frames. ZigBee may secure messages transmitted over a single hop using secured MAC data frames, but for multi-hop messaging ZigBee relies upon upper layers (such as the NWK layer) for security. The MAC layer uses the Advanced Encryption Standard (AES) as its core cryptographic algorithm and describes a variety of security suites that use the AES algorithm. These suites can protect the confidentiality, integrity, and authenticity of MAC frames. The MAC layer does the security processing, but the upper layers, which set up the keys and determine the security levels to use, control this processing. When the MAC layer transmits (receives) a frame with security enabled, it looks at the destination (source) of the frame, retrieves the key associated with that destination (source), and then uses this key to process the frame according to the security suite designated for the key being used. Each key is associated with a single security suite and the MAC frame header has a bit that specifies whether security for a frame is enabled or disabled.
Network Routing Overview
Perhaps the most straightforward way to think of the ZigBee routing algorithm is as a hierarchical routing strategy with table-driven optimizations applied where possible.
The network layer builds upon the IEEE 802.15.4 MAC's features to allow extensibility of coverage. Additional clusters can be added; networks can be consolidated or split up.
The ZigBee application layer consists of the APS sub-layer, the ZDO 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. Another responsibility of the APS sub-layer is discovery, which is the ability to determine which responsibilities of the ZDO include defining the role of the device within the network (e.g., ZigBee coordinator or end device), initiating and/or responding to binding requests and establishing a secure relationship between network devices. The manufacturer-defined application objects implement the actual applications according to the ZigBee-defined application descriptions
Patrick Kinney (firstname.lastname@example.org) is an Independent Consultant specializing in Wireless Communications. Previously he was the Vice President of Communication Technologies at Invensys responsible for directing communication efforts throughout Invensys's divisions. He received a Bachelors of Science in Electrical Engineering from the University of Notre Dame, Notre Dame Indiana. He has 26 years experience in the design and development and of communication systems and products. He is the Secretary of the IEEE P802.15 Working Group for Wireless Personal Area Networks and vice-chair of the IEEE 802.15.4 Task Group. He is also a Working Group Chair and the Secretary of the ZigBee Alliance, an association of companies working together to create a very low-cost, very low power consumption, two-way, wireless communications standard.
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