It is with mesh networking where Bluetooth has seen perhaps its biggest step forward. In fact, the SIG itself describes the addition of mesh networking in 2017 as a ‘paradigm shift’ with it introducing Bluetooth technology to a host of new sectors, particularly in the ‘smart’ and Internet of Things (IoT) markets.
As Woolley, who is Developer Relations Manager EMEA for the SIG, explains, mesh networking is a topology enabling the creation of large-scale networks that could conceivably contain thousands of devices.
“Bluetooth mesh can handle up to 32,767 things, or nodes, in its network,” he continues. “But communication between devices is not limited to those devices that are in direct radio range, which is normally the issue with radio communications.
“Devices send messages to communicate, and messages bounce across the network from device to device – it’s called relaying – until they reach their destination. A mesh is like a spider’s web that can cover very large areas; entire airports, office blocks, collections of buildings.
“The number of hops you can do across the network is 127, and Bluetooth LE, which powers the communication beneath Bluetooth mesh, has a range of hundreds of metres. If you do 127 x 50-100 metres, you have quite a lot of range and you can cover large areas. That’s what ‘large-scale’ means in the context of Bluetooth mesh.”
By lifting the hood on this ‘managed flooding’ approach to message communication, a simple yet clever system is revealed. Devices are first provisioned onto the network using a series of security keys, a process undertaken via an application on smartphone or tablet.
To communicate across the mesh network, a group address sends a message – an act known as ‘publishing’ – to select nodes, which then process, or ‘subscribe’, that message. In almost every example, it’s about one node talking to a collection of other nodes on a publish and subscribe basis. Messages reach their destination via multiple paths on the mesh, creating an extremely reliable communication mechanism.
Initial use cases for Bluetooth’s mesh networks have seen them utilised to deliver automated systems in smart buildings, such as temperature or lighting control. It has also been deployed as a catalyst for wireless sensor networks, venturing here into the manufacturing sector. It is the lighting example that Woolley uses to demonstrate how mesh networking works on the ground.
“Imagine you’ve got a dozen lights in a meeting room,” he explains. “You do some configuration, where you say to the lights as you install them, ‘By the way, I want you to subscribe to ‘meeting room A lights’’. That’s the name of the group address. You’re telling these devices to pay attention to any message that’s addressed to ‘meeting room A lights’. They pay attention and if they see a message sent, they will respond.
“The light switches in the room, or the dimmers, are also Bluetooth mesh nodes. You configure them to publish their messages to ‘meeting room A lights’, the same group address. If you then twist the dimmer switch or press the button, it’s going to transmit a message address to ‘meeting room A lights’. The lights in that room have been told to pay attention to messages addressed to that group, so they will respond.
“The important point here is that while we have this concept of groups, the groups are not defined in terms of their membership. The light switch doesn’t know which lights are members of that group. The lights themselves don’t know what switches are controlling them. This is very advantageous because it means you can make changes and you don’t have to reconfigure tables of information or all the switches. That’s publish and subscribe.”
