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BLE Connection Establishment Procedure | BLE connection Process

This page describes BLE (Bluetooth Low Energy) Connection Establishment Procedure. The messages exchanged between BLE master (i.e. initiator) and slave (i.e. advertiser) to establish BLE connection process are also described.

Introduction:
Bluetooth Low Energy (BLE) is a wireless PAN (personal area network) technology designed, developed and maintained by Bluetooth SIG (Special Interest Group). Bluetooth is widely used in various applications across industries viz. healthcare, security, fitness, entertainment etc. Few of the BLE devices include proximity sensors, fitness devices and heart rate monitors etc. It is also used in mobile phones, laptops, tablets for data exchange.

Link layer of BLE protocol stack is responsible for advertising, scanning, and creating/maintaining connections. The role of BLE devices changes in peer to peer (i.e. Unicast) or broadcast modes. The common roles are as follows.
• Advertiser/Scanner (Initiator)
• Slave/Master
• Broadcaster/Observer.
BLE Link Layer States
The figure-1 depicts BLE device states >>. The device will be in any one of these states which include Standby state, Advertising state, Scanning state, Initiating state, Connection State and Synchronization state. BLE connection process depends on role of the BLE devices.

BLE Connection Establishment Procedure | BLE connection Process

BLE connection establishment procedure

Let us understand BLE connection establishment procedure. We will look into BLE peer to peer or unicast connection process.
➤(Discovery phase: ) Initially discovery process takes place. As a result devices are aware of each other's presence. After this BLE connection process starts.
➤(Connecting phase : ) Then scanner selects preferred advertiser based on advertising data which include device name, service UUID, RSSI etc. Now the device is called "Initiator" which responds to advertising packet with "CONNECT_REQ" packet.
• This "CONNECT_REQ" packet as defined in v4.2 carries parameters which are useful for connection which include frequency hopping sequence, connection interval, slave latency, supervision timeout etc. Connection interval refers to time between two consecutive events. Once the CONNECT_REQ packet is transmitted by initiator or received by advertiser, the BLE devices are said to be connected.
• (As defined in V5.1), The CONNECT_IND and the AUX_CONNECT_REQ PDUs are sent by the Link Layer in the Initiating state and received by the Link Layer in the Advertising state. The AUX_CONNECT_RSP PDU is sent by the Link Layer in the Advertising state and received by the Link Layer in the Initiating state.
➤(Connected phase : ) Once connection is established between "master" and "slave", they can start exchange of data using data packets at regular intervals known as "connection events". The timing of connection events is determined by two parameters viz. connection interval (i.e. "connInterval") and slave latency (i.e. "connSlaveLatency" ).

References:-

➤BLUETOOTH CORE SPECIFICATION Version 4.2/5.1

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

Also refer bluetooth tutorial covering following sub topics:
Main Page  Frequency  PHY Layer  MAC layer  Stack  Power classes  Security  products  Bluetooth Vs BLE  Bluetooth vs zigbee   Bluetooth Vs WiFi vs NFC vs RFID  Difference between Bluetooth Versions 

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