Zigbee, Thread, Matter and hubs
Zigbee, Thread and Matter are three different things that sometimes share a radio or a house. This lesson shows a coordinator dongle, a host and a bridge, and what crosses the boundary.
A dongle is a radio, a host is a computer
A coordinator dongle is a Zigbee radio on a USB stick that has taken the coordinator role. The computer it is plugged into runs controller software, such as Zigbee2MQTT or the ZHA integration of Home Assistant, which talks to the dongle and to the rest of the home system. The host is not the coordinator.
The software lists each device by its clusters and reads and commands them through the dongle. Which products it understands depends on the adapter's firmware and on what the software knows about each product.
Thread shares a radio, not a network
Thread runs on the same kind of 802.15.4 radio and carries IPv6 packets. Zigbee does not carry IP. A firmware is one or the other, so sharing a radio chip does not make a device speak both.
Matter is not a radio
Matter is an application protocol that runs over an IP network: Wi-Fi, Thread or Ethernet, with Bluetooth Low Energy commonly used for setup. A Zigbee device is therefore not a Matter device. A bridge sits on the boundary between the two networks and exposes selected Zigbee functions as Matter ones. It translates what it knows how to translate, and a function it does not know does not cross.
What is not promised
Support is not a guarantee. Zigbee2MQTT, ZHA and vendor bridges differ in which clusters they expose, which devices they pair and how, and which version of the standard they were certified against. Certification aims at interoperating; the cluster and the version still decide whether a given light dims.
The MQTT course covers the messages Zigbee2MQTT publishes once a device is known to it. The next lesson asks what the evidence says when something stops working.
Common mistakes
- Calling the host the coordinator. The coordinator role is on the dongle's radio. The host runs the software that uses it.
- Treating Thread and Zigbee as one network because the radio is the same. The firmware makes it one or the other, and the packets differ.
- Expecting a bridge to make a Zigbee device a Matter device. A bridge exposes the functions it supports and nothing else.
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