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Bluetooth Protocol Stack

2 min read

Bluetooth Stack Overview

The Bluetooth stack is divided into three main sections:

  1. Application Layer

  2. Host Stack (Software Protocols)

  3. Controller Stack (Firmware/Hardware)

1. Application Layer

This is where user-level applications operate. Examples include:

  • Audio Applications – For streaming music.

  • Network (NW) Applications – For sharing internet connections.

  • Telephony Applications – For managing voice calls.

  • vCal/vCard Applications – For sharing calendar events and contacts.

  • Management Applications – For controlling and managing Bluetooth services and settings.

2. Host Stack (Software Protocols)

These protocols enable communication between the application layer and the controller:

  • L2CAP (Logical Link Control and Adaptation Protocol)

    • Adapts different application needs to the Bluetooth baseband.

    • Most upper-layer protocols pass through L2CAP.

  • RFCOMM (Radio Frequency Communication)

    • Emulates serial cable communication.

    • Commonly used in profiles like file transfer and headsets.

  • SDP (Service Discovery Protocol)

    • Enables Bluetooth devices to discover services offered by other devices (e.g., file sharing support).

  • BNEP (Bluetooth Network Encapsulation Protocol)

    • Used for sending Ethernet packets.

    • Supports Personal Area Networking (PAN).

  • OBEX (Object Exchange Protocol)

    • Facilitates file transfers and object exchange.

  • PPP (Point-to-Point Protocol)

    • Supports dial-up networking over Bluetooth.

  • TCS BIN & AT Commands

    • TCS BIN: Manages call control in telephony.

    • AT Commands: Used to control modems (e.g., in headsets and phones).

  • Audio

    • Sends audio streams directly to the controller, bypassing L2CAP.

  • Control

    • Handles management tasks like pairing, role switching, and device configuration.

3. Controller Stack (Firmware/Hardware)

Responsible for low-level communication and transmission:

  • Host Controller Interface (HCI)

    • Acts as the interface between the Host Stack and Controller Stack.

    • Transports commands, data, and events.

  • Link Manager

    • Manages link setup, authentication, encryption, and Quality of Service (QoS) negotiation.

  • Baseband

    • Handles packet conversion for wireless transmission.

    • Includes functions like error correction and flow control.

  • Radio

    • The physical transmitter and receiver operating in the 2.4 GHz ISM band.

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