BLE States: Understanding Bluetooth Low Energy State Diagram

This page describes BLE (Bluetooth Low Energy) states and the BLE state diagram. The BLE states include Standby, Advertising, Scanning, Initiating, Connection, and Synchronization.

Introduction to BLE

BLE (Bluetooth Low Energy) is a standard defined by the Bluetooth SIG. The link layer is the part or layer that directly interfaces with the Physical Layer. It’s responsible for advertising, scanning, creating, and maintaining connections between Master and Slave devices.

BLE Link Layer States

The operation of the BLE Link Layer can be described in terms of a state diagram or machine, as shown in the figure above. Let’s understand these BLE states:

• The Link Layer state machine allows only one state to be active at a time.
• The Link layer may have multiple instances of the link layer state machine.
• It shall have at least one state machine which supports one of the advertising or scanning states.

BLE States | BLE (Bluetooth Low Energy) State Diagram or Machine

• Standby State: There is no transmission or reception of packets in this state. This state can be entered from any other BLE state.

• Advertising State: A BLE device in this state is called an “Advertiser.” This state can be reached from the “standby state.” The link layer will transmit advertising packets and listen to and respond to responses triggered by these advertising packets.

• Scanning State: In this state, the link layer listens for advertising packets from other advertising devices. The BLE device in this state is known as a “scanner.” This state can be reached from the “standby state.”

• Initiating State: The BLE device in this state is known as an “initiator.” This BLE state can be reached from the “standby state.” The link layer listens for advertising physical packets from specific BLE devices and responds to these packets to initiate a connection with another device.

• Connection State: This state can be reached either from the “initiating state” or the “advertising state.” In this connection state, the BLE device has one of two roles: master or slave.

  • When the connection is entered from the “initiating state,” the device will be in the master role.
  • When the connection is entered from the “advertising state,” the device will be in the slave role.

  In the master role, the link layer will communicate with the device in the slave role and define the timing of transmissions.

• Synchronization State: This state can be entered from the “standby state.” The link layer in this state listens for periodic channel packets from a specified device transmitting periodic advertising.

References:

BLUETOOTH CORE SPECIFICATION Version 5.1

Previous versions of Bluetooth 5.0 or Bluetooth Low Energy (BLE)