What is Zigbee? How the Zigbee mesh protocol works

Zigbee is a low-power wireless mesh protocol for sensors, meters and controllers. It runs on the IEEE 802.15.4 radio standard, usually at 2.4 GHz, and sends small frames at 250 kbit/s. Mains-powered devices act as routers that relay frames for their neighbours, so readings hop from device to device until they reach one coordinator in a gateway, and the network finds a new path when a router disappears. Battery devices sleep most of the time and can run for years. The Connectivity Standards Alliance (formerly the Zigbee Alliance) maintains the specification, and Zigbee 3.0, ratified at the end of 2015, is the version most installed and current devices carry.

Zigbee at a glance

Coordinator, routers and end devices

A network has exactly one coordinator. The number of routers decides how well the mesh covers a building: every router adds coverage and alternative paths. Do not assume that every mains-powered device is a router; check the node type in its datasheet. End devices never relay, so a floor of battery sensors with no router near them depends on the routers on other floors.

How the Zigbee mesh routes and repairs itself

When a device needs a path to another, it can broadcast a route request, and the routers that pass it on build a route table entry for the best path found. Because most traffic in a sensor network goes to the coordinator, the coordinator usually advertises many-to-one routes instead: every router learns its next hop towards the coordinator from one broadcast, and the coordinator returns replies by source routing.

Self-healing means that a broken link triggers a new route discovery and the frame takes another path. It works only where another path exists. If a router is switched off, isolated for maintenance or removed, the end devices that used it as their parent must find a new parent within range. If there is none, they stop reporting until the router comes back.

Each hop transmits the frame again on the same channel. A reading that crosses three hops uses the channel three times, so a long chain of routers along a corridor fills the channel faster than a flat mesh with several paths to the gateway. A practical design rule is to place routers so that every area has at least two routers within one hop.

Zigbee 3.0, clusters and attributes

Before Zigbee 3.0, devices were certified for one application profile, such as Home Automation or Smart Energy, and profiles did not always work together. Zigbee 3.0 merged the home and building profiles into one, with common rules for joining, security and finding devices. Devices have been certified to Zigbee 3.0 since 2016, and it is what most installed and current devices carry. On 18 November 2025 the Connectivity Standards Alliance announced Zigbee 4.0 and Suzi, a sub-GHz variant.

What a device can report is defined by the Zigbee Cluster Library (ZCL). A cluster is a group of attributes and commands for one function, identified by a number:

Two devices can both be Zigbee 3.0 certified and support different clusters or different optional attributes. A plug that reports power in the Electrical Measurement cluster but no energy total in the Metering cluster cannot give you kWh without integration in the gateway. Read the list of clusters and attributes before choosing a device, not only the certification logo. Values are scaled integers: the Metering cluster's summation has a multiplier and a divisor that turn the raw count into kWh.

Devices send readings by attribute reporting: the gateway configures each attribute with a minimum interval, a maximum interval and a reportable change, and the device reports when the value moves by that much or when the maximum interval passes. Those three numbers decide how fresh the data is and how busy the channel gets.

Zigbee security and joining

Every frame on a Zigbee network is encrypted and authenticated with AES-128 using the network key. The trust centre, normally the coordinator, gives a new device the network key when it joins, protected by a link key.

Older devices used a well-known default link key, so anyone listening during a join could learn the network key. Zigbee 3.0 adds install codes: a code printed on the device, from which the trust centre derives a unique link key, so the network key never travels protected only by a publicly known key. Use install codes where the devices support them, open the network for joining only while you add devices, and keep a record of which devices joined.

Zigbee and Wi-Fi on 2.4 GHz

Zigbee channels 11 to 26 are 5 MHz apart from 2405 to 2480 MHz. Wi-Fi channels 1, 6 and 11 cover most of the band, and Zigbee channels 15, 20, 25 and 26 sit in the gaps between them. A Zigbee channel that overlaps a busy access point loses frames at the edge of the mesh. Survey the Wi-Fi channels in use before choosing the Zigbee channel, and again when the site adds access points. The Zigbee vs LoRaWAN guide gives the full channel plan and the failure modes to watch for.

Zigbee compared with other wireless protocols

Matter, the newer smart-home standard, runs over Thread and Wi-Fi, not over Zigbee; Zigbee devices reach Matter systems through a bridge. For sensors spread across a campus or below ground, a long-range network such as LoRaWAN suits better, and many sites use both.

Worked example: covering a plant room and an office floor

A two-storey building has 40 circuits to monitor in two distribution boards on the first floor, 12 temperature sensors spread across that floor's 2,500 m² of offices, and a gateway in the ground-floor comms room. The electricity monitors in both boards are mains-powered routers. EpiSensor's average for one mains-powered device is about 1,000 m² of commercial floor, so 2,500 m² needs three routers for single coverage and about five, spread evenly, for every sensor to have two possible parents. The two board monitors provide two; three mains-powered plugs or relays spread across the rest of the floor provide the others. A link budget for the steel board door, with the wireless link budget calculator, shows whether a router outside the board is needed so the monitors inside can reach the mesh.

Zigbee with EpiSensor

EpiSensor hardware uses Zigbee for every wireless device. The ZGW-20 Gateway is the coordinator and runs Edge, which stores and processes the readings on site. Every mains-powered EpiSensor device, such as the ZEM electricity monitor, routes for the mesh; each reaches up to 50 m indoors and 300 m outdoors, and one Gateway carries up to 250 devices. Third-party Zigbee devices join the same network, and the Zigbee device list shows how each one connects to Edge and which clusters it reports.