BLE Generic Access Profile

The Generic Access Profile defines how Bluetooth devices find each other, connect, and interact. It defines the parameters for how the devices display their presence to one another, establish links once discovered, pair and authenticate, and their roles when transferring information after connection.

GAP Roles

In Bluetooth Low Energy devices can operate as connected devices which pair and exchange data, or Beacons. In either case, their device roles fall under Central devices and Peripheral devices.

Central vs. Peripheral Devices

Central devices are the user device which is central in the network topology and can establish connections between multiple Peripheral nodes. Typically a device such as a computer or mobile device with greater processing power and memory.

Peripheral devices are low-resource devices in the network which can have connections established with Central devices. Peripheral devices can only be connected to a single other device, while the Central device can maintain connections to multiple Peripheral devices. Each peripheral device fulfills a service defined by the GATT.

Beacons

Beacons are low-power Bluetooth devices that advertise their data at regular intervals. The packets contain the device ID, and in their payload can contain data such as telemetry or URL for the scanner.

These can be used in public scenarios such as retail for sending notifications to user devices with retail information, as well as retaining some informatics such as interaction telemetry.

Broadcaster vs. Observer

In a Beacon system, the Broadcaster is typically the BLE device advertising its presence and data packet, in a one-way exchange.

The Observer is the user device scanning for beacons in the area and viewing their advertised data. No data is sent from the Observer, and it will digest the Beacon data.

Advertising

Advertising Data

Advertising Data is a mandatory 31 byte payload that is constantly broadcast to central devices within range to advertise the peripheral device's existence.

The device will set an advertising interval and broadcast the Advertising Data periodically. The listening device can scan the advertised device for an additional payload, the Scan Response Data.

Scan Response Data

Scan Response Data is an optional 31 byte payload that the peripheral can deliver when the Central device scans an advertised device within range. This optional payload can contain additional data to supplement that advertising data, such as device name, manufacturer, etc.