Characteristic

A characteristic contains a value, properties, and configuration information. Characteristic is the combination of characteristic properties, characteristic declaration, characteristic value, and a descriptor. Characteristic properties define the level of access that characteristic grants. For example, if a characteristic is read-only it will be defined in the properties. The characteristic declaration can be seen as a characteristic overview where the name, description, type and the requirements of the characteristic is mentioned. Descriptors are used to define a characteristic value.

The following diagram shows a view of the BLE characteristics:

Heart Rate Measurement characteristic with overview, properties, security and descriptor

The example in the figure is describing a Heart Rate Measurement characteristic. The overview describes the functionality of the characteristics and the requirement level. The requirement tells if it is mandatory or optional for the service. The properties show the access-level of this characteristic. In this particular scenario, the characteristic is only used to notify. The descriptor identifies the value or permits configurations of the GATT server with respect to the characteristic value.