Learning a Bit About ZigBee, and Passing it On

I recently got involved with a project where ZigBee was a candidate solution, and had to sharpen what little I previously knew about it. Here's a short summary of what I picked up about the wireless technology with the cute name.

From my CWNA days, I knew that ZigBee:

• is the the IEEE 802.15.4 standard


• plays in the 2.4 GHz spectrum


• uses narrow-band channels


• is low-power, with batteries that last years


• can use dynamic mesh topology for efficiency, interference avoidance


• is typically associated with sensors, building controls

But that's where my knowledge ended.

What I recently learned about ZigBee:

• The ZigBee Alliance is great resource for all things 802.15.4


• Coexistence between ZigBee and WiFi tends to be a natural point of concern for environments that have big WLAN and might want to also use ZigBee. Here are excellent whitepapers on the topic from The Alliance and from Schneider Electric.


• ZigBee has recently announced IPv6 support, and will be deep in Smart Energy systems


• This is an important slide for IP network-minded folk that need to know how ZigBee can interplay with IP

My specific project involved a company called Salto Systems, who builds their own protocol on ZigBee. I was looking at Salto's ZigBee-based door locks. I learned the following about the Salto topology, which is probably fairly typical of ZigBee systems:

• There is a Control Server that keeps it all going, used for monitoring and config


• The server talks to Gateways, which are powered by standard PoE and in many ways are just another endpoint on the LAN from the network perspective


• Each Gateway can feed up to 6 Nodes, and by extension up to 96 wireless locks (Each Node wirelessly services up to 16 locks)


• Gateways connect to Nodes via RS485 bus for data and power. These runs can be standard UTP, but because they are not home run to data closets, they do bring a new wiring paradigm where used


• There are a number of topologies that can be arrived at between Gateways and Nodes, and lots of daisy-chaining is possible


• Each Wireless Lock needs to be within 15 meters of a Node, with clear line of site between Locks and Nodes

That's pretty much it, although the Salto thing is just one ZigBee case study. It's pretty clear that there is much more to be learned about this fascinating technology that typically doesn't make it to my own wireless radar.

Here's a nice, basic video that contrasts Zigbee with WiFi, although it's a bit dated on it's 802.11 rates: http://www.youtube.com/watch?v=buV11ZPJ7MQ