Bluetooth Mesh Protocol Stack Layers and their functions
This page covers Bluetooth Mesh Protocol Stack Layers. It mentions functions of protocol layers of bluetooth mesh stack.
Introduction: The bluetooth mesh profile and mesh model specifications have been published offically on 18th July 2017 by Bluetooth SIG. It enables use of BLE (Bluetooth Low Energy) for many to many communications between nodes. It is used for home automation, lighting, sensor based networks and other applications.
Previous versions of bluetooth supported one to one and one to many topologies. Bluetooth mesh has been developed to support many to many topology. It runs on existing stack of bluetooth. Devices once joined the bluetooth mesh network are known as "nodes". The other devices who have not joined the network are known as "unprovisioned" devices. Without any connection, these nodes relay messages to each other using "advertising" and "scanning" states.
The different nodes with their functionalities are relay node, low power node, friend node and proxy node.
• Relay Node : This node type can retransmit the messages which are broadcasted by other BLE nodes. This allows messages to extend their reach and traverse further in the network.
• Low Power Node (LPN) : These power constraint nodes stay asleep for most of the time. They are mainly used for message transmissions.
• Friend Node : These nodes cash messages so that they can deliver them to power constraint LPN nodes when they wake up. Friend nodes are always ON and listen to all the broadcast messages.
• Proxy node : It implements BLE and mesh stack. It uses GATT which allows communication between non-mesh device and mesh device possible.
The messages are used by BLE mesh nodes for communication with each other. These messages are used for various jobs viz. to control nodes, to relay information and to report status. These massages are categorized into acknowledged and unacknowledged types.
The addresses are used to identify source node and destination node of the message. The different types of addresses are unicast, group address and virtual address.
Protocol layers of Bluetooth mesh stack
The figure-2 depicts layers of bluetooth mesh stack. Let us understand functions of each of these protocol layers.
➨Model layer : This layer addresses model implementations, their behaviours, messages, states and its bindings.
➨Foundation model layer : This layer is concerned with network configuration and management models.
➨Access layer : It defines format of application data and how higher layer applications can use the upper transport layer.
➨Upper transport layer : This layer is responsible for encryption, decryption and authentication etc. This layer also manages transport control messages such as heartbeat, friendship etc.
➨Lower transport layer : This layer handles segmentation of packets from upper transport layer and reassembly of packets from bearer layer.
➨Network layer : It defines addressing mechanism used for transport layer messages. It takes care of message addressing towards one or more elements.
➨Bearer layer : It defines how network messages are transported between nodes and how mesh packets (i.e. PDUs) are handled inside the mesh. There are two types of bearers viz. advertising and GATT bearer.
➨BLE core specification : It defines building blocks required by developers to create interoperable devices which make up bluetooth ecosystem. It is developed, updated and managed by Bluetooth SIG (Special Interest Group) working groups. The latest release is BLE version 5.2 published on 31st Dec. 2019. This BLE layer uses advertising and scanning features. It also uses GATT bearer for proxy nodes. These bluetooth core specifications can be downloaded from bluetooth.com >>.
Bluetooth Mesh related Links
Bluetooth RELATED LINKS
BLE (Bluetooth Low Energy) Links
➤Bluetooth v4.2 versus v5.0 >>
➤Bluetooth v5.0 versus v5.1 >>
➤BLE states and state diagram >>
➤BLE advertising and data channels >>
➤BLE protocol stack architecture >>
➤BLE advertising message format >>
➤BLE connection process >>