Hardware Reference
In-Depth Information
ZigBee
Sometimes (and unfairly) refered to as “the other Z protocol,” ZigBee (
http://www.zigbee.org
) is a protocol that uses
RF to communicate between devices at a range of between 10 and 100 meters. Unlike most other systems, there is no
separate controller necessary, and all devices can become a coordinator of the network (ZC), a router (ZR) or a end
point device (ZED).
5
In this way they are connected in a mesh formation, allowing the range to be naturally extended
to other parts of the house. It also supports security with 128-bit keys and, with chips being available from many
suppliers, they are comparatively cheap.
Politically speaking, ZigBee have an alliance (called, not unsurprisingly, the ZigBee Alliance), which provides a
focal point for the specification, standards, and details of the 600+ products available from over 400 different companies.
Because membership is open to all, the low barrier to entry has provided some innovative products such as AlertMe,
LG's air conditioners, and energy monitors along with the usual range of buttons, lights, dimmers, and sensors.
Linux Software
By being more open than Z-Wave, with the specification being freely available, the range of software should have
eclipsed Z-Wave. But didn't! This is because the ZigBee Alliance included a single clause that requires all licensees
using the ZigBee mark to be members of the alliance. And membership of the alliance costs money. Loads of money!
And clause 2c of the GPL (under which Linux kernel is written) states:
You must cause the whole of the work to be licensed at no charge to all third parties under the terms
of this License.
Therefore, it is not possible to include ZigBee in the kernel. Some projects have tried calling themselves Xbee to
avoid this, and had short lives. Others (
http://sourceforge.net/apps/trac/linux-zigbee
) have moved away from
ZigBee and toward other radio-based protocols, such as IPSO and 6LoWPAN.
Naturally, there is nothing preventing developers from working on libraries that are incorporated into the kernel
by the end user, but this raises the barrier to entry somewhat. One such project is:
http://support.robotis.com/en/software/zigbee_sdk/zig2serial/linux.htm
It is a valiant effort but, like the others, destined to be deprecated unless the alliance introduces a zero-cost tier
(like Bluetooth did), which allows the code to be included in the mainline kernel, and so reach mass adoption.
The Differences with Z-Wave
It seems that coders only need one common letter to start asking this question, as if it might be a fork or there's some
juicy gossip associated with development politics. In fact, ZigBee is a similar protocol only insomuch as it uses RF
to communicate from a hub to a set of similarly purposed devices. (And they both begin with “Z”!) But to say one
is better than other is wrong, as they are intended for different purposes. The same questions that should be asked
when considering whether to use X10 lighting or Hue, should be asked here as a larger question of “which is the best
solution for me?”
For the most part, Z-Wave devices have better compatibility between themselves. As much as a closed shop
might cause chagrin, it has ensured a set of devices that are happy to talk to each other—and being hardware, it's not
as if one could easily make changes to the firmware. Seeing as we are able to communicate freely with both Z-Wave
and ZigBee devices such philosophical standpoints are moot. Instead, it comes down to the use case. If you want
devices from a number of different manufacturers, and you don't have the ability to pretest their compatibility, then
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