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How large can a ZigBee network be? In a few years, a typical house might conceivably have 100 or more devices, while a large office building or factory could contain tens of thousands of ZigBee nodes. Theoretically, a single ZigBee network might address more than 1018 devices, though 65,000 is the limit imposed by IEEE 802.15.4.

At the bottom of the ZigBee network hierarchy is a type of node called a ZigBee End Device (ZED), which can perform only a single monitor or control function. The ZED communicates with nodes called ZigBee Routers (ZR). These can perform monitoring or control tasks, but they can also function as a router or repeater to pass a message along to another ZR or to the ZigBee Coordinator (ZC). Each network has one single ZC, which initiates the network formation.

Each ZigBee device includes the radio along with an embedded controller, the IEEE and ZigBee stacks, and minimum memory (both RAM and ROM). All can be created using low-cost, 8-bit microcontrollers that are battery powered.

ZigBee was designed from the start to use very little electrical power. In general, ZigBee protocols do this by minimizing the time the radio is on.

In most devices and applications, users will expect battery life that's measured in years. For applications with very low duty cycles -- such as automated meter reading, where a device is active less than 1% of the time -- battery usefulness may be limited only by the battery's own shelf life. This could mean the advent of single-chip devices that automatically transmit data when needed and run for years. For some types of devices, it may be most appropriate to replace the entire unit, not just the battery. The potential for medical or environmental monitors is extraordinarily bright.


The idea for ZigBee started in the late 1990s, when many engineers realized that both Wi-Fi and Bluetooth would be ill-suited to many applications. In particular, many engineers wanted to design ad hoc networks of digital radios that could organize themselves without requiring external configuration or network administration. The IEEE 802.15.4 standard was completed in 2003 and ratified in late 2004.

The ZigBee Alliance (www.zigbee.org) is an industry association that has branded and is promoting new uses for this wireless networking standard, in a fashion similar to how the Wi-Fi Alliance has pushed the Wi-Fi standard. Formed in 2002, the alliance coordinates activities and regulates and promotes the proposed standard and related technologies. More than 175 companies have joined the group.

The 802 Wireless Landscape
The chart below maps ZigBee and other IEEE 802 wireless standards according to their applications and speeds.

The 802 Wireless Landscape
Source: The ZigBee Alliance

See the complete Faces of Mobile IT special report.

Kay is a Computerworld contributing writer in Worcester, Mass. You can contact him at russkay@charter.net.

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Special Report

The Faces of Mobile IT

Different types of mobile workers, such as road warriors, telecommuters and blue-collar workers, need different forms of IT support.

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