Bluetooth Low Energy (BLE) Link Layer Operating States (v4.2/v5.0/v5.1/v5.2)

The operation of the Link Layer can be described in terms of a state machine.


BLEv4.2:









Standby: The Link Layer in the Standby State does not transmit or receive any packets.


Advertising: The Link Layer in the Advertising State will be transmitting advertising channel packets and possibly listening to and responding to responses triggered by these advertising channel packets. (Scan Request/Response)


Scanning: The Link Layer in the Scanning State will be listening for advertising channel packets from devices that are advertising.


Initiating: The Link Layer in the Initiating State will be listening for advertising channel packets from a specific device(s) and responding to these packets to initiate a connection with another device.


Connection: The Connection State can be entered either from the Initiating State or the Advertising State. Within the Connection State, two roles are defined:

Master Role => Standby –> Scanning –> Standby –> Initiating –> Connection

Slave Role => Standby –> Advertising –> Connection





BLEv5.0: The Link Layer State Machine of BLEv5.0 is same as BLEv4.2.





BLEv5.1:












Synchronization: The Link Layer in the Synchronization State will be listening for periodic physical channel packets forming a specific periodic advertising train, coming from a specified device that is transmitting periodic advertising. The Synchronization State can be entered from the Standby State. While in this State, the Host may direct the Link Layer to listen for isochronous data packets coming from a specified device that is transmitting a Broadcast Isochronous Group (BIG). A device that is in the Synchronization State and is receiving isochronous data packets is referred as a Synchronized Receiver.





BLEv5.2:









Isochronous Broadcasting: The Link Layer in the Isochronous Broadcasting State will transmit isochronous data packets on an isochronous physical channel. The Isochronous Broadcasting State can be entered from the Standby State. A device that is in the Isochronous Broadcasting State is referred as an Isochronous Broadcaster.


Reference: www.bluetooth.org