Zigbee Reference

The Coordinator creates the PAN, assigns network addresses, manages routing tables, and serves as the Trust Center for security key distribution. There is exactly one Coordinator per network. Routers relay data in the mesh network, manage child devices, and are always powered on (always-on). End Devices are sensors or actuators that communicate only through their parent router and cannot relay data for other nodes. Sleepy End Devices extend End Devices with sleep mode support, waking periodically to poll their parent for pending messages, achieving battery life measured in years.

In a Zigbee mesh network, Routers maintain routing tables and can forward packets through multiple hops to reach any destination. If a Router fails or a path becomes unavailable, the network automatically discovers alternative routes through other Routers. This self-healing behavior means that adding more Routers increases both network reliability and coverage range. The mesh topology is fundamentally different from star networks (like Wi-Fi) because there is no single point of failure beyond the Coordinator.

The ZCL defines standardized command and attribute groups organized by function. Each cluster has a numeric ID (e.g., On/Off is 0x0006, Level Control is 0x0008, Temperature Measurement is 0x0402) and specifies both server-side attributes and client-side commands. Because all Zigbee devices implement the same cluster definitions, a switch from one vendor can control a light from another vendor as long as both support the On/Off cluster. This cluster-based architecture is what enables multi-vendor interoperability in Zigbee ecosystems.

Binding creates a direct communication link between a source endpoint and a destination endpoint. After binding, the source device can send cluster commands directly to the destination without specifying the address each time. Group binding allows sending commands to a group address, reaching all devices that have joined that group. Reporting configuration enables automatic attribute reports (e.g., temperature every 60 seconds or when it changes by 0.5 degrees) from the bound source to the destination. Find and Bind (EZ-Mode) automates this process through a discovery protocol.

Zigbee uses AES-128 encryption at the network layer. The Trust Center (Coordinator) generates and distributes the Network Key to all authorized devices. In the default centralized security model, new devices receive the Network Key during joining. Install Codes provide stronger security by using a per-device pre-shared key (16 bytes + 2-byte CRC) that is registered on the Trust Center before the device joins. The Install Code derives a unique Link Key for the key exchange, preventing eavesdropping during the joining process. Zigbee 3.0 mandates Install Code support.

A Sleepy End Device (SED) is an End Device with RX-on-when-idle set to false, meaning its radio is off most of the time. It wakes periodically based on the long poll interval (e.g., every 60 seconds) to check with its parent Router for any pending messages. The aging timeout (e.g., 64 minutes) defines how long the parent keeps messages buffered. This aggressive sleep schedule, combined with the 2.4 GHz IEEE 802.15.4 radio's low transmit power, enables SEDs to run on coin cell batteries for years, making them ideal for sensors and switches.

Zigbee 3.0 unifies all previous application profiles (Home Automation, Light Link, Building Automation, etc.) under a single standard with Base Device Behavior (BDB). Before 3.0, devices from different profiles could not interoperate even on the same network. Zigbee 3.0 mandates Install Code security, introduces EZ-Mode commissioning for simplified device pairing, and ensures all certified devices are interoperable regardless of their application domain. Products certified after 2016 must comply with Zigbee 3.0.

Green Power is a Zigbee profile for ultra-low-power devices that harvest energy from button presses, motion, light, or temperature differentials instead of using batteries. Green Power Devices (GPDs) send short, unidirectional transmissions triggered by energy harvesting events. A Green Power Proxy (typically a Router) relays these frames into the Zigbee network. Because GPDs have no persistent power, they use simplified security with pre-commissioned keys and cannot maintain network state. This profile is used in energy-harvesting switches like EnOcean-based products.