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When it comes to the Smart Home, communication protocols may not be the sexy part, but they're doing all the work behind the scenes.  It's great to monitor and measure something, but if you can't transfer the data into a usable form for viewing on the web or communicating with other devices, all you have is 1's and 0's escaping into the ether.  Plus, without communication networks, how would you be able to control your home with your smart phone!

Communication protocols work to form home networks, which fall into 2 camps: Hardwire (like powerline) or RF (like wi-fi).  You can also have a combination of both types of protocols (hardwire and RF) in a home network.  Devices using communication protocols are either :

• Monitoring devices - Like a computer receiving data from a smart meter.  See our list of home energy monitors here.
• Controlling devices - Like automatically turning off you lights with your iPhone (the Schlage Link iPhone app utilizes a home controller using Z-Wave).
• Monitor and Control - Like having a internet programmable thermostat that you monitor the temperature and control the thermostat accordingly like an Ecobee thermostat or a 3M Radio Thermostat (both use Wi-Fi)

An important concept in home networking is the Mesh Network, where each node (device) in the network also acts as a router to move information along.

As an example of how these protocols are used in the home, I utilize several types of communication protocols in my home with my TED 5000 energy monitor and Ecobee programmable thermostat (which uses WiFi).  The TED 5000 (see how TED 5000 works) utilizes powerline communication to communicate from the breaker panel to the gateway.  The gateway is hardwired to my router, but it has an option (which I have) to include a wireless LED display which communicates with the Gateway using ZigBee (see below).  I will note that people commenting on our TED 5000 article say that the TED powerline communications interfere with X10 communications.  Here is what Trev had to do to bypass that problem (note: Trev sounds pretty advanced, so I don't recommend doing what he did unless you know what you're doing):

At that point, another nasty issue arose which has also been discussed here – interference with X10 signals. Virtually every light in our house is automated by a custom SBC that monitors passive IR sensors in all living areas to control the lighting. The system has been rock solid for over 10 years, but the TED 5000 played havoc with the X10 modules right off the bat.

Changing data update rates, X10 house codes, and breaker positions for the MTU didn’t help, and I was ready to return the TED but decided to try one more idea … isolating and filtering the MTU and Gateway on their own AC circuit. This is only possible because I have access BEHIND the breaker box. I pulled one leg of the AC (120v) outside the box, through an X10 XPPF noise filter to an outlet strip where I plugged in the Gateway and supplied power back to the white and black wires of the MTU, then ran ethernet from Gateway to the nearby HA computer.

So if you already have a TED 5000 or other energy monitor that uses powerline carrier installed, you probably should look at a technology other than X10 for your home automation needs!

Below are different smart home communication protocols:

•   HomePlug Power Alliance (Powerline) - The HomePlug website has a nice section on how they interact with the smart home.  And for instances where communications can't take place over the home's electrical wiring, HomePlug has teamed up with Wi-Fi Alliance to round out the offering.

•   Insteon (Powerline and RF) - Insteon was created by SmartLabs, the same company that owns the home automation website SmartHome.  Here is a link for a great overview for How Insteon Works.  Insteon devices are backward-compatible with X-10 devices.

•   Wi-Fi - (RF) - We're familiar with Wi-Fi because it's how we all access this blog at our favorite coffee shop!  But along with allowing us to access the web without cables, wi-fi can also be used to control smart homes.   Wi-Fi may be facing some tough competition though because a recent study by GE has shown Wi-Fi to be more expensive and consume more power than Zigbee products (keep reading and I have a link to the article discussing the GE study).  I have an Ecobee internet programmable thermostat and it uses WiFi to communicate over my home's wireless router.  I can control it with an iPhone app  from anywhere I have an internet connection.  I'm not sure if this can be done with ZigBee or Z-Wave (without another home controller).

•   X-10 - (Powerline) - X-10 was one of the first home automation communication protocols (started by Pico Electronics in the 1970's), but has been plagued by limitations.  Wikipedia has a good list of X-1o's weak points; which include: commands getting lost, relatively slow, limited functionality, and interference and lack of encryption.  X-10 did a great job of helping to advance home automation, but it seems to be surpassed by other technologies now on the market.  To prove how long X-10 has been around, here's an old archived article how X-10 was chosen by a GE home automation product called The HomeMinder.....back in 1986!  It's amazing to me that while technology has advance, we're basically still talking about the same thing 25 years later (make sure you read about the smart grid software to help customers use energy in off-peak hours).

•   ZigBee (RF) - Zigbee uses a wireless mesh network.  Open source technology.  An advantage over standard wi-fi is that Zigbee chips use less power than wi-fi chips.  Has a higher bandwidth (more handle more data) than Z-Wave.

•   Z-Wave (RF) - Proprietary technology built by Zensys that uses mesh network.

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Here's a great post from 2008 comparing X-10 vs. Insteon, ZigBee, and Z-Wave and here's one from 2010 comparing ZigBee and Z-wave.

CNet has an excellent post titled "Take Control of your digital home" that does a great job comparing the different technologies on the market:

While X-10 remains the most popular home-automation technology--it is estimated that there are 10 million X-10 devices in U.S. homes--it looks like it may have reached the end of its run because it simply doesn't deliver the reliability, the ease of use, and the convenience to attract a mainstream consumer audience. This year you'll see products based on several new technologies popping up at Home Depot and RadioShack.The first, Smarthome's Insteon, is a dual-band technology--it uses both power line and RF. One of its chief advantages is that it is backward-compatible with X-10 and is designed to eventually replace the older technology. While it is a logical successor, two upstarts, Zigbee and Z-Wave, are hoping to dethrone it. Both are based on RF wireless, but Zigbee has garnered the most press, largely because it is based on an open specification (IEEE 802.15.4) and has lined up 100 companies that plan to use the technology. In response, Zensys, the developer of the Z-Wave technology, recently formed a Z-Wave Alliance consisting of about 60 companies that will use the technology in products and ensure that they are all interoperable.

And..

Unlike Insteon, Zigbee and Z-Wave are both strictly wireless, and they are not backward-compatible with X-10. Zigbee uses the 2.4GHz (global) and 915MHz (Americas) and has throughput of 40Kbps to 250Kbps; Z-Wave uses the 908.42MHz (United States) band and has a data throughput of 9.6Kbps. Products based on Z-Wave have been available for about three years, but those based on Insteon and Zigbee should start showing up at home improvement and electronics stores later this year, all starting at around $20.

Back in December of 2010, Earth2Tech had a nice blog covering GE's decision to pick ZigBee over Wi-Fi for home communication.  From the article on why ZigBee was a winner:

Consider it another notch in ZigBee’s home energy belt. Utilities around the country have chosen ZigBee as the preferred technology to link smart meters and devices in the home, largely on the strength of its low power requirements and cheaper chipsets compared to Wi-Fi and other technologies built for higher-bandwidth applications.

So will Zigbee run away with the lead for smart homes, or will one of the other protocols win out?

The article on X-10 written in the 80's that I linked to above closes with:  "It's been predicted that eventually we'll all have some kind of universal controller in our homes, a unit that ties together all of our electronic appliances, entertainment equipment, and telephones. Fortunately, we can get a taste of the future right now with the easy-to-use products already available."  And it seems that statement is still true a quarter-century later.

Smart home communication protocols are evolving fast, enabling device manufacturers to bring products to the market faster and cheaper.  Let's hope the future finally gets here soon.