Although most IT professionals, as well as a majority of consumers, are familiar with the Bluetooth wireless data-communications standard, very few are aware of the new ZigBee wireless data standard. In time this awareness will grow, but right now ZigBee is in the early stage of the adoption process; it's just beginning to be rolled out in industrial applications, with consumer-oriented applications soon to follow.

The ZigBee standard differs from Bluetooth in many ways, but essentially it addresses a different set of market requirements.

First and foremost, ZigBee targets inexpensive, low-power applications. Integrated ZigBee chipsets, with battery power slated to last six months to two years, are available for US$1 or less. In addition, ZigBee-enabled devices are networked readily: As many as 65,536 such devices can be connected in a star topology or a peer-to-peer configuration. The data rate for this cost-effective and low-power technology is 20 kbit/s to 250 kbit/s.
ZigBee, based on the IEEE 802.15.4 standard, performs very well in environments with a low signal-to-noise ratio. Radio signals extend 10 meters to 40 meters, depending on settings and signal strength).

The ZigBee standard supports various network topologies fully - including mesh configurations with routes between nodes dynamically modified based on the availability of intermediate routing nodes - and is optimised for timing-critical applications and power management. It takes less than 30 msec to join a network, less than 15 msec to go from sleeping to active and less than 15 msec to access a channel.

There are three categories of ZigBee network node:

  • ZigBee coordinator. Only one is required for each ZigBee network; initiates network formation and acts as the network coordinator; may act as a router once network is formed.
  • ZigBee router. Optional component that may associate with a ZigBee coordinator or another ZigBee router; participates in multihop routing of messages.
  • ZigBee end device. Optional network component that does not participate in routing.
The ZigBee protocol stack requires at least an 8-bit microcontroller to implement the core functions. The full protocol stack occupies less than 32 kbyte of space, with node-only implementations requiring less than 4 kbyte. Coordinators require extra RAM because of such features as the device database and the transaction and pairing tables.

ZigBee technology is used in everything from industrial light switches to light fixtures, appliances, home electronics and even light bulbs themselves. Because of the wireless nature of the communications, installing ZigBee devices in existing environments is a no-brainer, and the technology's support for mesh networking allows high connectivity and automatic routing of the data sent among devices. ZigBee's low-power requirements mean low maintenance (batteries need changing only every two years), which makes the technology suitable for consumer-oriented products.

One area where ZigBee is used with great success is in intelligent transportation systems. ZigBee wireless data transfer is being used to communicate between buses and bus stations, allowing arrivals and departures to be displayed.

ZigBee modules in the bus and the station communicate in a way that prevents accidental miscommunication with other station units. Depending on the bus location, the mobile ZigBee unit establishes a link only with the ZigBee unit in the first station on the route; all others are ignored. In addition, because the mobile unit knows the exact address of the station unit, communication is established quickly. Thus, there is virtually no delay before the bus is detected approaching a specific bus station, and this leads to the bus's arrival and departure times being updated accurately.

Because of its standardisation and low-cost and -power requirements, and the ease with which ZigBee-enabled devices are networked, ZigBee is poised to establish a position alongside Bluetooth as a critical enabling component of ubiquitous, networked commercial and residential devices for years to come. As ZigBee-enabled devices make their way into the market, consumers may someday refer to ZigBee the way they now refer to Bluetooth.

Greenland is director for systems and product integration at Telargo. This article appeared in Network World.