BLE Architecture — Layer by Layer
1) Application Layer
Your device logic.
- Sensors, device behavior, data processing
- Uses BLE to communicate data Example: breath sensor sends measurement.
2) GATT (Generic Attribute Profile)
Defines how data is organized and exchanged.
- Services
- Characteristics
- Read / Write / Notify / Indicate Example: Heart Rate Service, custom sensor service.
3) ATT (Attribute Protocol)
Protocol underneath GATT.
- Moves attributes between devices
- Client/server data model Think: transport for GATT data.
4) GAP (Generic Access Profile)
Defines how devices find and connect.
- Advertising
- Scanning
- Connecting
- Roles (Central / Peripheral) Controls visibility & connection behavior.
5) L2CAP
Data multiplexing layer.
- Splits and reassembles packets
- Handles MTU sizes
- Supports multiple logical channels Usually hidden by stack.
6) Link Layer (LL)
Controls radio behavior.
- Advertising packets
- Connection timing
- Channel hopping
- Retransmissions Critical for power & stability.
7) Physical Layer (PHY)
Actual radio transmission.
- 2.4 GHz band
- 1M, 2M, or coded PHY
- Modulation and channels Real RF layer.