2. Network Reliability

Even in a medium-sized home, it is likely that two nodes that need to communicate are not within direct RF communication range. Mesh networking provides an elegant solution to this problem. Figure 2 shows a typical mesh network, with a solid line illustrating the communications path between two nodes that are not able to communicate directly.

The mesh network also serves as the basis for Z-Wave's self-healing functionality. RF communications links vary over time due to their strong correlation to the physical environment. For example, when doors open or close, furniture is moved, or there are simply many people moving around, RF links may fail because the environment is changing. In these situations the self-healing mechanisms in the Z-Wave technology automatically reroute messages via other nodes to their destinations.

Standards

Standardization also plays an important role in this rapidly growing market. A set of wireless technologies targeted at monitoring and control is being developed in standard IEEE-802.15.4. However, while the first specification was ratified in 2003, it appears to have failed so far to set the standard for wireless home controls. While West Technology Research Group predicts rapid market growth for IEEE 802.15.4 overall, it concludes that its market will be highly fragmented. In 2009, the 15.4 communication stack option with the largest following is predicted to capture only a little over 10 percent of the entire 15.4 market. There are multiple reasons for this: critical technical challenges still remain unsolved, there is a kind of a slow "design by committee" atmosphere, and there are also still a very large number of options in the associated communication stacks.

The 2.4 GHz variant of the IEEE 802.15.4 standard is the one most implemented and promoted. Obviously, it is a victim of significant interference from both WLAN and Bluetooth devices. This interference is leading to packet loss of over 90 percent in typical real-world application scenarios. Solutions in the 915 MHz band, such as Z-Wave, do not have this problem.

However, Zensys believes that those benefits are not enough to explain the accomplishments of Z-Wave. Overall, the key to Z-Wave's success is how it answers the key challenges for home control outlined above. Z-Wave is based on FSK RF technology and should be much less complex than IEEE 802.15.4, while still providing good RF performance and good indoor range. Lower complexity leads to lower chip sizes and lower power consumption, reducing solution costs both now and in the future.

Zero Management Of The Mesh Network

The central challenge in network management is that homeowners don't fully comprehend how devices work as part of a mesh network. It is critical, therefore, that there be no need for manual network management. Accordingly, the Z-Wave mesh network is self-organizing and self-healing.

Given the requirements in home controls, the Source Routing Algorithm (SRA) provides a good balance and has therefore been selected for Z-Wave as the basis of its self-organizing and self-healing mesh networking technology. "Self-organizing" means that nodes are capable of discovering their neighbors and distributing information to others automatically. In a "self-healing" network, nodes are capable of redirecting traffic if parts of the mesh are down.

Re-routing in a Z-Wave mesh network

The diagram of re-routing in a Z-wave network (above) shows an example where communication between the garage door and Lamp A fails. A stainless steel refrigerator door is being opened (illustrated by the red line). Z-Wave uses mesh networking to automatically reroute the message using the nodes in the hallway.

Many home control devices are battery-operated and need to function for many years without requiring battery changes. The Z-Wave solution is specifically designed in both hardware and software to cater to battery operation. As one example, Z-Wave can operate on a thermostat for 10 years using just a single pair of AAA batteries.

Zensys is offering Z-Wave development kits with development modules, tools such as network sniffers, complete documentation and comprehensive sample applications. OEMs can typically build fully-functional product prototypes in well under three months.

Extensive Z-Wave information, including detailed product reviews, can be found at zwaveworld.com, an independent web site serving the Z-Wave community. The Z-Wave Alliance is the affinity group of more than 125 OEMs that are building products based on Z-Wave (z-wavewavealliance.org).

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