ZigBee, the emerging low-cost sensor network based on IEEE 802.15.4 wireless standards in the 2.4 GHz band is on the brink of a big step. The ZigBee 1.0 specification is poised for publication soon: "It is expected in the near future," according to a Zigbee Alliance spokesperson.

The IEEE 802.15.4 standard defines the basic communication method for sensor networks but more work is required to produce a marketable product. The Zigbee Alliance, a consortium of technology companies, does this work for 802.15.4, in much the same way that the Wi-Fi Alliance commercialises the IEEE 802.11 wireless LAN standards.

The forthcoming Zigbee 1.0 specification will define the network, security and application software layers above the physical and MAC layers defined in 802.15.4. The Alliance also plans to announce a conformance and interoperability certification program, according to alliance board member Jon Adams, who is also director of radio technology and strategy at Freescale Semiconductor.

The future of 802.15.4 has been called into question, since variants of 802.15.4 are appearing in products, while the Zigbee spec is still not completed. The Zigbee Alliance, however, believes the spec will be in time to unite the industry.

Zigbee applications
ZigBee represents an industry initiative to enable the construction of business and residential network applications using low-cost, low-power sensors that run on batteries with very long lives. Among these applications are lighting control; heating, ventilating and air conditioning (HVAC) environmental management; and industrial sensors.

Hotel sensor networks, for example, could automatically determine when there's no one in a room and then turn off lights, heat and air conditioning to conserve energy. Similarly, hotels could keep a guest's profile with room temperature preference on file, and the room could automatically be programmed to adjust to that environment upon guest check-in.

For other possible Zigbee applications, read Wireless sensors get down and dirty.

Network layer: filling in the 802.15.4 gaps
At the network layer, ZigBee specifies how the sensor network forms (in a mesh configuration), heals itself, grows, and routes messages, Adams explains. For security, 802.15.4 specifies 128-bit Advanced Encryption Standard encryption but nothing about how to manage encryption keys. So ZigBee specifies key management.

At the application layer, ZigBee 1.0 has already defined basic applications for lighting, HVAC and industrial sensors; developers can simply add their own look and feel. For application developers who choose not to use the standard ZigBee profile, there are API calls in the 1.0 spec that define rules for how applications speak to the ZigBee system, Adams says.

Zigbee has received backing from Bob Metcalfe, inventor of Ethernet and now a venture capitalist and pundit. He, at least, believes that a unified Zigbee specification will spark a radical new market for low-cost, long battery-life sensors carrying out radically new jobs.

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