Alliance moves toward seamless connected home

One of the ongoing limitations to domestic IoT adoption is incompatibility. There are many connected lights, doorbells, appliances, and whatnot available to consumers, but they form freestanding islands of functionality that are difficult to blend into a unified smart-home setup. The Zigbee Alliance, though, may be close to solving that […]

One of the ongoing limitations to domestic IoT adoption is incompatibility. There are many connected lights, doorbells, appliances, and whatnot available to consumers, but they form freestanding islands of functionality that are difficult to blend into a unified smart-home setup. The Zigbee Alliance, though, may be close to solving that problem with its emerging open standard for the Connected Home over IP (CHIP).

The alliance’s involvement, however, does not mean that this is simply a veiled effort to promote Zigbee as the core communications standard for home automation. In fact, while Zigbee’s 802.15.4 mesh will be supported, that’s not until later. Project CHIP’s initial release calls for Wi-Fi or Thread for its core communications, and Bluetooth Low Energy (BLE) to simplify device commissioning and setup. Instead, the project’s goal is to come up with a unifying application layer that developers can leverage regardless of the underlying hardware choices, so that applications will be able to communicate with any devices built to the CHIP standard, subject to user permission.

That permission is a part of a key goal for the project: application and device security. It has become clear that security is critical to the success of home automation, safeguarding user information, as well as ensuring the integrity of their home’s operation. No one wants a repeat of the baby monitor hacking debacle.

The CHIP Project’s overall architecture (Figure 1) shows the full diversity of its connectivity options. Virtually every type of established IP interface will be supported. Higher up, the IPv6 format is utilized, offering the opportunity for every device to have a unique IP address if desired, and both TCP and UDP protocols are supported.

pyrmid chart showing the CHIP Project architectureFigure 1 The CHIP Project architecture supports all the major IP-based communications standards used in home networking. Source: Zigbee Alliance

All these lower layers, of course, are already defined. What the alliance is developing that is unique to the CHIP Project is the application layer. This is where all the various implementations of the IoT for home automation will come together.

The application layer breaks into seven main components, as shown in Figure 2.

pyramid chart of the CHIP project’s application layerFigure 2 The project’s application layer provides the mechanisms that simplify interoperability across the home automation industry. Source: Zigbee Alliance

Each layer has a specific function. The application layer defines the device’s high order business logic. A lighting application, for example, might include features for turning on/off the bulb and setting its color characteristics. The data model provides primitives that describe the device’s various functions, and the data structures with which the application layer interacts. The interaction model describes the set of actions that can be performed by reading or writing attributes to the data model’s structures.

Once the application constructs an action using the interaction model, the action framing layer creates a packed binary message formatted for transmission. The action frame then passes to the security layer where it is encrypted and signed so that the payload can be secured and authenticated by both sender and receiver. Next, the message framing and routing layer constructs the payload by adding both required and optional header fields that specify the message’s properties and some routing. This payload goes to the IP framing and transport management layer to get sent to the desired transport protocol.


This structure provides numerous mechanisms to facilitate interoperability. The data and interaction models, for instance, provide a standardized way of defining what a device can do, so that higher-level programs have a way of readily accessing their features. This will help simplify the creation of applications that aggregate multiple devices into a coordinated system, regardless of their manufacturing origin. The approach also sets a basic expectation for security that users can depend upon. This should help ease consumer worries and help build trust that the home automation market will require.

The Zigbee Alliance has opened the CHIP project to the industry to help ensure buy-in when it is complete. Already more than 145 active member companies are involved in hammering out the details, working in 30 cross-functional teams focusing on interoperability issues. Further, the alliance is making its results publicly available as open-source files in a GitHub repository so that even developers who are not formally involved can participate. The idea is to “try out” the developing standard in an implementation-first approach to help prove that the standards are practical.

The CHIP project is on track for formal release at the end of 2020. If the definition effort is successful at ensuring interoperability, and is widely adopted by developers, the standard could help stimulate the home automation market. If connected devices for home automation can be made so that they simply work together out of the box, the major barrier to consumer adoption of the IoT will fall.

Rich Quinnell is a retired engineer and writer, and former Editor-in-Chief at EDN.

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