How Bluetooth Mesh worksFollow article
Basically, there are four different types of nodes in a Bluetooth mesh network. The relay node receives messages and sends them on, but each message is sent only once. The message itself has a configurable expiration counter, after which the message is not retransmitted.
Relay nodes are an elementary function in all non-low power nodes. Proxy nodes are the interface to BLE devices that do not have their own Bluetooth mesh stack. With their BLE-GATT function they are used to operate or configure the mesh.
Low-Power nodes are the nodes with the lowest power consumption. Low power consumption is essential for battery operation or energy collecting systems. For this reason, the low-power nodes are inactive for most of their time. In order not to miss any messages, the low power node looks for a single so-called Friend node, which caches the messages for it. Friend nodes have a secure power supply and buffer the messages for one or more low-power nodes. They send these messages on request of the low-power node and pass on its data.
The integration of a node into the mesh network, called 'Provisioning and Configuration', is carried out via the GATT connection (PB-GATT) or via an advertising channel (PB-ADV) as a transmitter. Only (PB-ADV) is suitable for smartphones or tablets. In a 'Provisioning' process, the device is searched for and integrated into the mesh with the appropriate keys. The primary element of the node gets a unique 'unicast' address and the node gets a network key. ‘Configuration' is the assignment of the node to its function and group.
The data transfer in the Bluetooth Mesh takes place via a so-called Managed Flood procedure. All messages are in a cache list. A reception is compared with the cache list, the message is only sent once. Each message receives a TTL value (Time to Level), which is decremented each time it is forwarded (maximum: 126). The messages are distributed according to the publishing and subscribing procedure. Publishing is the sending of a message. Subscribing is a configuration that allows selected messages to be sent to specific addresses for processing. Typically, messages are addressed to groups or virtual addresses (unicast, multicast and broadcast).
Structure of the node: Nodes can have several elements, but at least one element - the primary element. For example, it can be several sensors or lamps. Each element has a unique address, the 'Unicast address'. Models in turn define the functionality of a node. There are three types: Server, Client and Control. The states of the individual elements are determined by 'States'. For example, there are on, off, state transition, instantaneous or transition time, i.e. over a period of time.
Whole scenarios of states or states are determined in the scenes. Certain scenes can also be saved or restored here. As an example, one can imagine the position of actuators of the windows in a large greenhouse. In the second element of the node the lighting and in the third the irrigation could be controlled, while other nodes report back the temperature, humidity, brightness and soil moisture.
Manufacturers like Silicon Labs are leading partners in this technologies.