When contemplating a home-automation project — as with many other technology decisions — the right place to start is ensuring you’re purchasing something that is future proof.
As a veteran of the networking industry, future proofing is a technology decision that has some well-understood rules. Computer networking benefits from open standards that drive interoperability, and our customers in turn benefit from fierce competition as well as the knowledge that an open, generally interoperable standard reduces their risk. Even if you buy an Ethernet switch from a vendor that stops supporting it (or worse, goes out of business), a switch can provide years of useful service because it, by definition, works with many devices that come after it.
Home automation depends heavily on tying together sensors, controllers, and an application framework. Unfortunately, the lesson of having common standards to drive that networking has yet to become apparent in the products available on the market. There are several network technologies that are used in home automation today, but none is fully suitable for creating a market. One of the reasons why there is extensive hobbyist work done by programmers writing and modifying code on the Arduino and Raspberry Pi platforms is that the market for shrink-wrapped automation devices has been unable to grow without a technology framework that allows good ideas to be developed and “plug into” an existing system.
Home automation standards can be divided into two groups: technologies that provide a transport (call it layers 1-4 of the OSI model) and higher-layer protocols that support applications. In this post, I’ll compare the various home automation standards and explain why there is not yet a clear winner.
Application-layer protocols
Two protocols provide both a transport layer and bundle that transport layer with a higher-layer application system.
- X10. X10 is transmitted on power lines or radio frequencies, and consists of a simple protocol constrained by the computing power available when it was invented in 1975. The X10 protocol can transmit at about 20 bits per second, which constrains the size of protocol packets, limits the number of “sophisticated” protocol operations such as acknowledgements, and the number of available devices. X10 equipment is cheap because of its simplicity, but it is basically a dead-end technology. With such a low data rate and fossilized protocol, X10 cannot easily be connected to IP networks unless an X10 “modem” is connected to a computer. If you want to dip your toe in the water of home automation, X10 is a good way to get started — after all, if you’re going to throw away everything you learn at first, it might as well be inexpensive.
- Insteon. Insteon is an evolution of the X10 protocol with significantly improved features and functionality. With sustained date rates of nearly 2,400 bits per second, the Insteon protocol is capable of much more than X10. It supports a much larger number of devices, and commands are acknowledged and retransmitted when necessary, leading to much-improved reliability when compared to X10. Although it represents a large step forward when compared to X10, Insteon still has relatively low bandwidth and can only be connected to an IP network through an Insteon powerline modem, which limits its ability to be connected to sophisticated devices. Like X10, Insteon devices are not able to use IP-based services.
- ZigBee. ZigBee uses the IEEE 802.15.4 transport layer, a self-organizing mesh topology that supports a data rate of up to 250 Kbps. ZigBee devices can either be full routers that pass messages between nodes, or they can be end devices that can act only as a leaf in the mesh. ZigBee has always had a strong focus on maximizing battery life and requires that devices operate for years on a single battery.
- Z-Wave. Z-Wave is a routed radio network that supports speeds of up to 40 kbps. Coverage areas may be built out of a mesh to enable protocol messages to reach beyond the range of a single device.
Transport protocols
Transport protocols are able to connect devices to a software management system, but they provide a network connection and no more. Mixing and matching multiple vendors is up to the software stack or two vendors working together to create interoperable systems.
- Bluetooth. Originally intended as a cable replacement for portable devices, Bluetooth supports data rates of up to 3 Mbps. (Bluetooth high-speed technologies in Bluetooth 4.0 are based on Wi-Fi technology and use a co-located Wi-Fi link for high speed transfer.) Bluetooth is a relatively short-range point-to-point technology, and connecting to an IP network requires use of a router.
- Wi-Fi. Wi-Fi is well-understood and proven technology. It has the highest data rates of any common transport layers at hundreds of megabits, but that speed comes at a relatively high cost in power consumption. (The Wi-Fi industry has developed several power-saving protocol features, and at one point I led a Wi-Fi Alliance task group that researched sophisticated power saving protocols.) Wi-Fi’s advantages in home automation are that it is ubiquitous. It is safe to assume that any home that is using automation will have full Wi-Fi coverage, and that Wi-Fi network will provide ready access to Internet-hosted services. Wi-Fi’s high data rate enables it to use existing network connections from the home to process and store reams of data. The major drawback for Wi-Fi is that many devices will need to be connected to power sources, though in the case of some devices such as automated power outlets, sufficient electrical power should be available.
- HomePlug. HomePlug is a power-line technology that encodes Ethernet frames over high frequency on the main carrier signal. It supports high data rates and presents an Ethernet interface at both ends of the power line. Extending a HomePlug network is easy — just plug in another network drop where it is required. Many automation devices, however, need to be installed without an Ethernet cable.
There are also several commercial products that are only available through a dealer network (Crestron, Control4, and AMX). Typically, these products are subject to tight control and do not allow for post-install modification without the involvement of the professional installer.
What it all means
Nothing’s perfect, and the state of home automation certainly illustrates the fragmented nature of the technology. We are a long way from the easy interoperability that I am accustomed to in the networking business, where a strong de facto standard enables multiple vendors to create technology that can be mixed together based on the needs of the business. If home automation is going to grow beyond hobbyist-driven one-off projects and become a market with off-the-shelf products, we need the home automation equivalent of what the LAMP stack was to the web: a standard set of protocols that is used by everybody.