Thread (network protocol)

Thread is an emerging standard for a smart home mesh network protocol. It was developed by a consortium of competing smart home companies, using IP version 6 over an IEEE 802.15.4 wireless network (on the 2.4 GHz spectrum). Thread is designed for low-power, fast, reliable messaging among IoT devices.

Thread performs the same job as existing smart home protocols Zigbee and Z-Wave, but unlike them, Thread eliminates the need for a central hub or bridge. Thread devices talk directly to each other in a wireless mesh configuration and can talk directly to any other IP-based device, including smart phones, tablets, computers, and Wi-Fi routers. Thread is the first low-power, wireless mesh networking protocol to allow low-power devices to use IP.

Thread is the required protocol for wireless networking of devices in the emerging Matter standard in smart homes.

The basic specifications for the Thread protocol are:

• Frequency band: 2.4 GHz
• Throughput: 250 Kbps
• Topology: Mesh
• Number of devices: 250 to 300
• One hop range: up to a few hundred meters (routers can extend range through multi-hop)

Since Thread is IP based, each Thread device has a MAC address and an IP address. Here is the overall protocol stack:

6 - Application layer (e.g., Matter)
5 - UDP
4 - IP Routing
3 - 6LoWPAN
2 - IEEE 802.15.4 MAC
1 - IEEE 802.15.4 PHY

Thread device roles: Router, End Device, Border Router

Devices on a Thread network are divided into two main categories--those plugged into power (i.e., a light bulb or smart plug) vs. those that are battery-powered (i.e., a motion sensor or a smart lock). Always-powered devices on a Thread network play the role of a router that forwards traffic along to other devices as needed. Any battery-powered device on a Thread network is called an "end device". An always-powered device that also connects to the internet (such as a smart speaker or Wi-Fi router) can, if it contains the necessary software capability, also act as a Thread "border router", passing messages between the Thread network and servers on the internet.

A smart home will usually want to have at least one border router so that its Thread-capable devices can reach the internet. A Thread border router is not usually going to be a dedicated device like a hub or bridge; instead, it is a feature that can be integrated into any powered device that has access to the internet. Any Thread-capable device should be able to use any border router to reach the internet, regardless of manufacturer.

Any device can be unplugged without ruining the network

The advantage of using a mesh network is that there is no single point of failure. Any device can be removed, and all the other devices should continue to work, although at least one border router must be present for devices to access the internet.

Thread network capacity (250+ devices)

A Thread network can support more the 250 devices. A Thread network can have as many as 64 routers (i.e., always-powered devices), although no more than 32 can be active simultaneously. Among the routers, multiple instances of border routers may exist, or none (if internet access is not required or available).

Applications that run on top of Thread

The new smart home standard, Matter, is an application that runs on top of a Thread network. Matter supports both Wi-Fi and Thread for connecting its devices, and its use of Thread means that there is no single point of failure in the home network--any one device may fail or be unplugged, but the rest of the network can continue to work normally. Other applications that may run over Thread include HomeKit, Google/Weave, or Open Thread, etc. Because it's an IP-based network, a Thread network could support multiple of these application laters running simultaneously.

Thread is fast and thus conserves battery life

Unlike earlier technologies, Thread has been optimized from its inception to run on low-power devices that require near real-time access to rapidly changing data, and thus to handle a high volume of data messages with minimal delay (latency). Early benchmarking of Thread, as compared with Zigbee and Bluetooth networks, show Thread networks to have much less delay, especially when scaled to large numbers of devices, and the quicker activity of Thread translates into less power usage, which is especially important for battery-driven devices.

Security cameras are not a fit for Thread

The one kind of smart home device currently in use that does not work well on Thread is security cameras, because those require high-bandwidth internet connections, whereas Thread is designed for much lower-bandwidth applications. Thread is specifically intended to do well for small, low-powered devices such as leak detectors, CO detectors, and motion sensors. Such devices may be left untouched and unused for months but need to spring into action reliably when required and need still to have battery life left when that happens. In addition to sensors, Thread is designed to send commands to devices such as door locks, window shades, light bulbs, and thermostats.

Thread traffic is encrypted

Finally, unlike with a bridge of hub, a Thread border router cannot read the traffic that it passes along, because all communications in a Thread network are encrypted.

Status of Thread

Supporting thread as of April 2023 are:

• Apple HomePod (border router)
• Apple HomePod Mini (border router)
• Apple TV 4K, 2021 or later (border router)
• Eve Energy smart plug
• Eve Window and Door sensors
• Eve Aqua
• Eve Light Switch
• Google Nest Wi-fi (border router)
• Google Nest Wi-Fi Pro (border router)
• Google Nest Hub Max (border router)
• Google 2nd-gen Nest Hub (border router)
• Nanoleaf Essentials A19 smart bulb
• Nanoleaf Essentials Smart Light Strip

Thread, and the Matter application layer which can run over it, are both emerging standards in 2023. The latest specifications of Thread as of April 2023 is version 1.3.0 in Feb. 2023 (540 pp), available by registering at the Thread Group.