Connect the Dots: Bluetooth LE Mesh Arrives, Finally

Create: 07/24/2017 - 14:35
Bluetooth LE Mesh

Bluetooth low energy (LE) Mesh took the long route, but it finally arrived last week, officially. Now developers of IoT solutions can use Bluetooth as the backbone of a low-power, wireless, peer-to-peer network for monitoring, tracking and control of sensor networks and assets at home, in buildings or on the factory floor.

Bluetooth is already ubiquitous, having started as a low-power, point-to-point communications solution that had high hopes, but quickly became relegated to headphone or mouse, keyboard duties. Other interfaces with mesh capability built in, like Zigbee and Z-Wave, took on the larger role of industrial, utility and, more recently, lighting control.

In the era of smartphones and the IoT, Bluetooth’s default position on the smartphone has increased its utility. In particular, Bluetooth is used to securely associate smartphones with devices. Once associated, the smartphone application can control those devices directly or over a Wi-Fi or cellular network.

Thread, Zigbee, Z-Wave and others, while secure and low power, have not been fully integrated into the smartphone ecosystem.

While waiting for the Bluetooth Special Interest Group (SIG) to develop a mesh protocol, IoT developers have considered using proprietary approaches, such as CSRmesh. This is now owned by Qualcomm, which bought CSR. The newly announced mesh protocol is supported by more than 150 companies.

Along with smartphone compatibility, a big plus of using Bluetooth Mesh is that devices and software can take advantage of Bluetooth beacons to track assets.

Why Mesh?

The importance of mesh capability has always been pretty clear: it lets every device in a network talk to any other device, in a peer-to-peer, many-to-many or broadcast fashion. In this way, a data packet can find its way to the far end of a network without having to go through a central hub. This extends the range of a network’s devices, and if implemented correctly, it enhances network robustness and reliability. A packet can be routed using any node within range, if the nearest one fails or is temporarily offline; it can still continue its journey.

Bluetooth Mesh protocol

Mesh networking lets any node route a message through the nearest available and compatible node. (Image source: Nordic Semiconductor).

The Bluetooth Mesh protocol uses a managed flood message relay architecture that is easy to deploy and is inherently multipath and self-healing for reliable message delivery. It can also scale to 32,000 nodes, so in the case of industrial lighting, a single switch can turn on hundreds (or thousands) of factory lights.

Security is strong: it uses 256-bit elliptic-curve cryptography and out-of-band authentication when provisioning a device, and messages are secured using AES-CCM. Encryption and authentication are done at the application and network layer.

Mesh Tradeoffs

The traditional downsides of mesh are protocol complexity, relative to point-to-point, which has a knock-on effect on memory and processing requirements, and of course power consumption. Power consumption for any given node is also affected by needing to forward packets for another node, when it would rather stay asleep and conserve its own power, especially if it’s running on a small, coin-cell battery that needs to last 10 years.

Bluetooth LE is low power by design, but adding mesh requires careful layout and planning to keep power consumption to a minimum. Thankfully, the SIG has already considered this. The managed flood messaging approach means that only mains-powered nodes serve as message relays, so battery-powered devices can remain inactive. IoT solution providers need to factor this into their network layout considerations.

Another factor that’s particularly important for mission-critical applications is latency. If a message needs to be acted upon in real time, such as when temperature reaches a critical level, the latencies add up as a message passes from node to node. Milliseconds count, so solution providers need to look closely at the inherent latencies of a mesh network and how to factor them in, reduce them or find a way to revert back to point-to-point instead for specific sensing nodes.

Getting started with Bluetooth Mesh

Bluetooth Mesh can be installed on legacy devices that are compatible with core specification version 4.0 or higher, that are designed to be upgraded in the field and that have enough memory. They must also support Generic Attribute (GATT) and Generic Access Profile (GAP) connections.

To get started, use a compatible kit, such as the nRF5 software development kit that Nordic recently announced in synch with the SIG’s mesh introduction. It has the full mesh core stack, configurable scanning intervals (3 ms to 10240 ms), duty cycle and advertisement intervals.

The wait for Bluetooth Mesh has been long and winding, but now that it’s here, IoT solution providers have the reassurance of knowing that what they develop for industrial applications can work for the home, industrial gateways and consumer smartphones. A small hop for messages: a big step for solution providers.

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Patrick Mannion
Patrick Mannion is an independent writer and content consultant who has been working in, studying, and writing about engineering and technology for over 25 years.

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