Embedded Computing Design - OpenSystems Media

Zigbee Alliance
alternate routes via neighbors, and they always deliver low latency
responses making them ideal for control networks where human
perception times are important (e.g., turning on a light when
entering a room).
Meshes are by far the best choice for most ZigBee control networks.
Meshes are populated by mains-powered control devices such as
motor controllers, lighting load controllers, pumps, and other large
load switching or controlling devices which are usually doubling
as network routers due to the fact that they’re mains-powered.
Input devices such as light switches, thermostats, and security
sensors can take advantage of the mains-powered network devices
and operate from batteries. Thus, the peel-n’-stick light switch or
temperature sensor, which runs for the shelf life of an inexpensive
alkaline cell is a real practicality with ZigBee.
Figure 3
position within the mesh, but go beyond tree in allowing for
additional routes to improve robustness. Meshes are expected to be
installed in buildings and facilities where the ZigBee Routers and
Coordinator are mains-powered. For these devices, the receivers
are always on, which allows the end devices (often battery-operated
sensors, buttons, or other input devices) to sleep at all times except
when an event occurs. Router/Coordinator devices hear all of their
neighbors, which allows them to develop neighbor tables that
record relative route quality (derived from signal strength) with
respect to neighbor address. Also, since addresses are generally
derived from their position in the mesh with respect to the
coordinator, a node can estimate a neighbor’s position in the mesh
based upon its address. Meshes heal easily due to the existence of
Jon Adams is chair of the ZigBee Alliance’s
Qualification Group and is the director
of Radio Technology and Strategy for the
Motorola SPS Wireless and Mobile Systems
Group. Jon has written and spoken on these
technologies and has provided regular
interviews about the topics with industry
analysts.
Contact Jon at jta@motorola.com.
Contact the alliance directly for membership and event details.
ZigBee Alliance
Tel: 925-275-6607 • Fax: 925-275-6691
Website: www.zigbee.org
RSC #17 @ www.embedded-computing.com/rsc
Embedded Computing Design Summer 2004 / 17