Structuring BLE Generic Attribute Profile Services

Design custom GATT services and characteristics to effectively organize data exchange between peripheral devices and central IoT gateways.

In this lesson, you will learn how to architect custom GATT services and characteristics to ensure efficient, data-dense communication between your IoT peripheral and central gateways.

The GATT Hierarchy

At the core of Bluetooth Low Energy (BLE) communication is the Generic Attribute Profile (GATT). Think of GATT as a hierarchical database schema. At the top level, you define a Service, which acts as a logical container for a specific function (e.g., "Environmental Sensing"). Inside the service, you place Characteristics, which represent the actual data endpoints (e.g., "Temperature Value").

Designing for Efficiency

When designing for IoT gateways, your goal is to minimize the number of airtime-consuming round trips. Instead of creating five separate characteristics to send temperature, humidity, pressure, altitude, and timestamps, you should pack these into a single structured characteristic.

Consider this data layout for an IoT sensor node:

struct __attribute__((packed)) SensorData {
    int16_t temperature;    // 0.1 deg C units
    uint16_t humidity;      // % units
    uint32_t timestamp;     // Epoch seconds
};

By mapping this struct directly to the Value field of a single GATT characteristic, the gateway receives a complete snapshot of the sensor state in one notification packet. This avoids the overhead of managing multiple attribute handles and reduces the power consumption of the peripheral’s radio.

Implementation Best Practices

Logical Grouping: Place related data under a unique Service UUID. Use standardized 16-bit UUIDs for common services to ensure interoperability, and reserve 128-bit vendor-specific UUIDs for proprietary telemetry.
Permissions and Properties: Set the property to NOTIFY or INDICATE for telemetry data. This allows the peripheral to push data to the gateway as soon as it is sampled, rather than forcing the gateway to poll the device repeatedly, which drains the peripheral's battery.
Client Characteristic Configuration Descriptor (CCCD): Always include a CCCD for characteristics that support notifications; it allows the gateway to toggle data streams on or off, preserving bandwidth when the gateway is busy with other tasks.

Key Takeaway: Efficient GATT design requires packing related data points into structured characteristics to minimize airtime and optimize battery life for embedded IoT endpoints.