4: ZigBee Applications > Attributes and Clusters

Attributes and Clusters

This page describes attributes and clusters, used in ZigBee application profiles. Fundamentally, attributes and clusters define the type of data that a device may exchange with other ZigBee devices. They therefore determine which network devices can communicate with each other.

Attributes

Each data item that passes between devices of a ZigBee network is called an attribute. Each attribute has its own unique identifier. For example, a switch device can have an attribute with identifier OnOff whose value represents the action to be performed: On (0xFF), Off (0x00), Toggle (0xF0).

Clusters

A number of attributes are grouped into a cluster, where each cluster has its own unique identifier. For example, for an HCL Switch Remote Control (SRC) device, there is a cluster with identifier OnOffSRC containing the attribute OnOff. Clusters may be mandatory or optional for a device to support.

A cluster may contain several attributes. For example, for an HCL Switching Load Controller (SLC) device, the cluster Output:StatusSLC contains 17 attributes. These describe the state of the controller, such as whether the SLC is On or Off, the total length of time that the load has been in the On state, the total power consumed, the voltage applied to the load.

Relation to Application Profiles

An Application Profile can have several associated clusters. For example, the Home Controls-Lighting (HCL) profile includes the clusters OnOffSRC and ProgramSRC for an SRC device.

The Application Profile defines which clusters are mandatory and which clusters are optional for the device. The clusters supported by a device determine the other devices with which it can communicate. For example, for two devices to operate together in temperature monitoring and control, the two devices must support compatible clusters concerned with temperature. The sensor device must have an output cluster containing the monitored temperature, and the controller must support an input cluster which can use a temperature to make control decisions. On the other hand, a device containing clusters concerned with temperature monitoring cannot communicate with a device containing clusters concerned with lighting levels.

	The messages exchanged by ZigBee devices identify which cluster is associated with the data payload of the message.

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