Since its introduction in 1994, Bluetooth technology has become one of the important technologies for short-range wireless communication. As the basis for realizing Bluetooth communication, the Bluetooth protocol stack defines various protocols and functions from the physical layer to the application layer.
The Bluetooth protocol stack is usually divided into the following layers, each of which is responsible for specific functions:
Physical Layer:
Responsible for sending and receiving radio waves, working in the 2.4GHz ISM band.
Defines modulation methods, frequency hopping, power control and other technologies.
Link Layer:
Responsible for device discovery, connection establishment and maintenance.
Provides basic control of data transmission, such as packet segmentation and reassembly, encryption and authentication.
Direct Access Transport Layer:
Includes the Logical Link Control and Adaptation Protocol (L2CAP), which is used for multiplexing, reassembly and service quality control of packet data.
Host Controller Interface (HCI):
Defines the command, event and data transmission interface between the host and the Bluetooth controller.
Logical Link Control and Adaptation Protocol (L2CAP):
Responsible for packet encapsulation and decapsulation, providing logical link control and data transmission services.
Attribute Protocol (ATT):
Used to discover and transmit attributes, especially for GATT (Generic Attribute Profile) services in BLE.
Generic Attribute Profile (GATT):
Defines a standard method for data exchange between BLE devices, which is applied to the discovery and access of various services and characteristics.
Generic Access Profile (GAP):
Responsible for basic operations such as device discovery, connection mode and security.
Application Layer:
Includes various Bluetooth application profiles, such as A2DP (Advanced Audio Distribution Profile), AVRCP (Audio and Video Remote Control Profile), HID (Human Interface Device), etc.