Για οποιον ενδιαφερεται να μαθει περισσοτερα για το zigbee protocol, ενα πολυ ωραιο άρθρο:
http://cocoontech.com/portal/articles/guides/home-automation/144-zigbee-101
If you are like most people, interested in technology and home automation you probably have been hearing more about ZigBee lately, but you probably are not exactly sure what ZigBee is and how it relates to home automation, and home energy monitoring. This article is intended to provide some background information on ZigBee and to dispel some of the false information that has been circulating about the technology. Maybe most of all it's meant to illustrate how ZigBee will impact the field of home automation, energy monitoring, and even personnel health care monitoring. While ZigBee has generally been flying under the radar, I feel that this technology is likely the most important and exiting technology to impact home automation since X-10.
I am a home automation enthusiast (I use CQC and HAI), a frequent contributor to CocoonTech (ano), and for my day job, I’m a Principal Wireless Analyst for a research firm called In-Stat where I cover wireless chip technology and cellular technologies. Because I’m in the middle of it all, I’m also in a good position to write such an article such as this.
Before we get started discussing ZigBee, let’s first discuss another wireless technology, Wi-Fi, so we can compare the evolution of this technology to ZigBee. In the mid-90’s, before Wi-Fi existed, several companies were selling wireless products that performed the function of what Wi-Fi does today, basically substituting a wireless connection for an Ethernet cable. At the time, a typical access point and client device together cost about $700, and since each manufacturer used a proprietary protocol over wireless, each company’s client would only communicate to that company’s client. Seeing this as a problem, the IEEE (Institute of Electronic and Electrical Engineers) got together with companies that made these products at the time, and after much debate and compromise, produced the 802.11b standard for wireless LANs in October 1999. Within a year, a handful of companies were making 802.11b devices, many more were making 802.11b chips, and you could purchase a wireless access point/client for under $250. Soon after, a non-profit group composed of member companies was formed to perform interoperability testing between devices from different companies. That group later went on to be called the Wi-Fi Alliance. Fast-forward ten years to present, and the shelf at Fry’s or Best Buy contains Wi-Fi products as far as the eye can see. Ninety nine percent of laptops made today have Wi-Fi as do 20% of cell phones. In-Stat forecasts over 450 million Wi-Fi devices will be shipped this year. This is what a technology standard can do in a several-year period.
Now lets move on to home automation and ZigBee. Home Automation arguably started in 1975 with X-10, but while it was a fantastic technology for the time and is still used today, the technology was limited, and admittedly, the number of home automation enthusiasts’ back then was also limited. Still enough people were interested in home automation that several companies thought there was enough market for “follow-on” products like UPB, Z-Wave, RadioRA, INSTEON, ALC and others. All are great products, all proprietary, and all designed by one company (and possibly licensed to others) to perform a specific task for the purpose of selling a product and making money. In terms of evolution, all are at the equivalent time of wireless LAN before the 802.11b standard was approved.
The Technology
So what is ZigBee and how does it fit into all this? ZigBee is a wireless standard and technology whose goal it is to provide low-speed connectivity (250Kbps max.) with a range of 150 feet and running from a single battery for several years. ZigBee also incorporates mesh technology so range can be extended, and over 64,000 devices can be incorporated into a network. ZigBee operates at 2.400–2.484 GHz, 902-928 MHz and 868.0–868.6 MHz. Overall, ZigBee is a much broader technology than Wi-Fi, since ZigBee can be a simple radio, a mesh transport network, and/or it can specify how applications communicate. Wi-Fi is just a transport of TCP/IP.
Like Shrek and an onion, ZigBee is composed of layers. At the lowest layer is the 802.15.4 physical radio that allows two ZigBee devices to connect via a radio link. These ZigBee radios can be made cheaply for only a few dollars, and currently Freescale and TI are major manufacturers of these radios. Normally one radio speaking to another isn’t very useful in and of itself, but with ZigBee there is a an application that will be very important, the replacement of infrared in remotes and TVs and audio equipment. This remote standard is called RF4CE and has advanced to the point where many large manufacturers are supporting it, including Philips, Sony, and Samsung. High-end equipment will be shipping with ZigBee soon, and lower-priced equipment will follow in a few years. Here is a press release from Sony announcing it:
http://www.sony.net/SonyInfo/News/Press/200903/09-0304E/index.html
The next layers up with ZigBee are the MAC and networking layers that specify how devices interoperate with each other using a self-forming mesh network. This is the ZigBee you’ve likely heard about, a mesh network of wireless devices all communicating. This standard is called the ZigBee Feature Set or the ZigBee Pro Feature Set, and a few companies have made products that based on this. Remember, this layer only gets data from any node to any other node, but it doesn’t specify what the data means, in other words, it doesn’t specify how to turn on a light. More on this below.
ZigBee Profiles
If you made it this far, your probably saying to yourself, “that’s well and good, but how do you turn on a light?” Where does that spec come from if it’s NOT in the ZigBee Feature Set or Pro Feature Set? We’ll that is the next layer above, the application layer that is also called the public profile. Currently there are five of these public profiles defined as follows:
ZIGBEE BUILDING AUTOMATION – The protocol specifies how to control lighting, heating, cooling and security in commercial buildings to save energy and provide safety.
ZIGBEE TELECOMMUNICATION SERVICES – This protocol specifies home mobile phones and devices will communicate.
ZIGBEE HEALTH CARE – The protocol provides a standard for interoperable wireless devices enabling secure and reliable monitoring and management of noncritical, low-acuity healthcare services targeted at chronic disease.
ZIGBEE SMART ENERGY – This offers utilities and energy service providers secure, easy-to-use wireless home area networks for managing energy and reading your meter remotely and securely.
ZIGBEE HOME AUTOMATION – Last but not least, you’re favorite and mine, this protocol specifies how to communicate with light switches, home thermostats, and load controllers. So this specifies the commands to dim a light, turn on a fan, etc.
Therefore, any light switch, for example, with the ZigBee Home Automation logo will interoperate with any other light switch or system that also displays the same logo but manufacturers are still also free to add proprietary features to their products over and above the standard feature set. So if Leviton wants to add a unique button or light to each of its switches for a feature only available on Leviton systems it can be added as long as the switch also supports the standard ZigBee Home Automation features.
So lets stop here a bit to recap, because it is a bit complex. ZigBee radios alone can be used for point-to-point communications, to provide a low-cost wire or infrared replacement. The RF4CE standard rides on ZigBee radios and specifies how TVs and home entertainment devices communicate. (But remember, no mesh here, just point-to-point and low-cost just like infrared.)
To have a mesh network, you need the ZigBee Feature Set that specifies how nodes communicate with each other in a network. A company can use the ZigBee Feature Set to build products, but unless these companies also use a public application layer, then realize these ZigBee products WILL NOT BE interoperable with ZigBee products from other companies. These ZigBee products have been out for a few years now, leading to the mistaken belief that no ZigBee products are interoperable. Not true.
To guarantee that a ZigBee product is interoperable with products from other companies, it must follow one of the application public protocols, and ONLY products using the SAME profile are certified to interoperate with each other. Even then, a company may add proprietary features on its products, over-and-above what the standard requires. A device or system can also support multiple profiles, for example, maybe both the ZigBee Home Automation profile AND the ZigBee Smart Energy profile.
For us home automation enthusiasts, the public profile to watch is the Zigbee Home Automation profile, signified by a big orange dot with a picture of a home on it. This profile specifies how you communicate to the following devices: On/Off Light Switch, Dimmer Switch, Light Sensor, Occupancy Sensor, Shade Controller, HVAC Unit, Temperature Sensor, Thermostat, Pump Controller, Flow Sensor, Pressure Sensor, Alarm Warning Device, Controlled Power Outlet, and a few other odds-and-ends. Currently, the ZigBee Home Automation profile supports up to about 500 nodes before it slows down, but this limit is sure to be increased as the standard matures.
Like Wi-Fi and the Wi-Fi Alliance, ZigBee has the ZigBee Alliance composed of over 300 member companies. The ZigBee Alliance helps to bring companies together to create the ZigBee standard. The ZigBee Alliance web site has a wealth of ZigBee info, including downloadable standards, pictures of the profile icons, etc. so please check it out here:
http://www.zigbee.org The ZigBee Alliance also certifies devices as meeting the standards and being interoperable. On August 19th 2009, the Alliance announced its first batch of 17 certified ZigBee Home Automation products from 10 manufacturers. By definition, all these ZigBee products are interoperable with each other.
After many years of standards definitions, ZigBee is really only starting. In Wi-Fi terms, we're back in 2000 when the first 802.11b products started to arrive. However, while Wi-Fi has gone from a few 100,000 units to 450 million in 10 years, ZigBee has the potential to exceed this in just a few years.
ZigBee Application Examples
ZigBee will replace all infrared in your remote controls and universal remotes will control all your ZigBee controlled audio and video equipment, plus ZigBee equipment will control each other. A ZigBee DVD player could turn on a monitor and set it to the DVD input automatically.
A nearby ZigBee light switch may also communicate with all your audio and video equipment allowing a central controller to control ALL your equipment and TVs in your house without a single IR emitter or RS-232 port.
ZigBee in your washer and dryer will tell your home controller when loads are complete. ZigBee in your electric meter will allow your utility to shut off your dryer during peak usage time.
ZigBee in your cell phone will allow you to control your TV, or any light switch in your house, or purchase a burger at McDonalds with electronic debit, or it will let your doctor monitor your ZigBee pacemaker over the cellular 3G network while you are anywhere in the world.
FAQ
What is ZigBee Pro?
ZigBee Pro is an optional feature set that can be added to ZigBee stack which adds significant improvements in network scalability, security, and ease-of-use, especially for larger, more complex networks. It’s not likely any of these PRO features will matter much in home ZigBee networks, but from what I hear from the ZigBee Alliance, the current ZigBee devices all include the PRO feature set. Don’t be surprised if PRO becomes part of the standard ZigBee stack as a required feature in the future.
ZigBee Pro replaces the ZigBee Feature Set with the ZigBee Pro feature set, and the ZigBee Home Automation public profile can work with either so for most people, it doesn’t matter if your device feature set is Pro or regular.
How do you configure a ZigBee network?
Like UPStart for UPB, or a Z-Wave remote for Z-Wave, configuration software (from 3rd parties) or other ZigBee devices will configure devices. For example in a Control4 system, devices are configured with an interface on your TV, but it could be configured with software on a computer and a ZigBee interface, or a ZigBee remote like Z-Wave uses.
How are ZigBee devices added to a network?
Similar to Bluetooth or UPB, you’ll have to push a button on the device while you add it to the system.
Is ZigBee secure?
ZigBee can use 128-bit AES security and can be VERY secure. This was a requirement early on since utilities are using ZigBee to read electric and gas meters and the technology has to be secure.
Does ZigBee interoperate with Z-Wave?
No. The two technologies use the same wireless frequencies, but that is where the similarity ends.
Do ZigBee devices have upgradable firmware?
Unlike Z-Wave or UPB, yes, ZigBee devices are upgradable, and even upgradable over the air. Pretty cool.
Does ZigBee interoperate with Wi-Fi?
No, but don’t be surprised if you see ZigBee radios appear in broadband gateways that cable (set-top boxes) and/or internet service providers install which usually also include Wi-Fi.
Conclusion
I hope this was helpful and invite you to please feel free to ask me any questions you have about ZigBee. If I don’t know the answer, I’ll find out for you.
Allen Nogee
Principal Analyst
Wireless Technology
In-Stat
