Bluetooth devices could soon have mesh networking capabilities

The Bluetooth SIG has published its specification for mesh networking using Bluetooth Low Energy.

Bluetooth is about to get some significant new mesh networking capabilities -- and the best bit is, you may not need new hardware to benefit from them.

Mesh networking will make it simpler to connect sensors across industrial sites, or to create smart home or building automation networks. Rather than wasting energy shouting to be heard by a distant gateway, devices will be able to whisper to their neighbors, asking them to pass messages.

It will offer a new way for devices to join the Internet of Things. Once a building has a mesh network to control lighting, say, other devices can use it as wireless infrastructure for other applications such as asset tracking and wayfinding, said Martin Woolley, technical program manager at Bluetooth SIG, the organization behind the Bluetooth standard.

Bluetooth treats mesh networking as just another networking topology built on Bluetooth Low Energy, so if you have a device that supports that, chances are a software update is all that's needed for it to join a mesh. That even goes for things like smartphones and tablets: If they support Bluetooth LE, then all they need to start meshing is an app.

In theory, Tuesday's publication of Version 1.0 of the Bluetooth mesh networking standard is the starting gun for the race to launch compatible devices, but in practice, that race is well under way.

The industry is already familiar with the specification's requirements, with around 120 companies participating in the working group to develop it, compared to 10 or 20 in a typical Bluetooth SIG working group, Woolley said.

Those requirements have already been tested, too. "We don't finish the spec then do some testing: We've already had 15 testing events where we've covered the whole spec," he said. Hardware modules with the Bluetooth mesh stack could be on the market in a matter of months, he said. Vendors might try to charge extra for the additional software, but Woolley said he wasn't aware of any additional patent licenses needed to access the new capabilities.

Not all nodes are created equal in a Bluetooth mesh network. Some -- controllers in light fittings, for example -- may have plentiful power while others -- light switches, say, or temperature sensors -- may need to run for years on one battery. The specification provides two ways for such devices to save their energy.

One is the "publish and subscribe" model for sending messages. A kitchen light switch, for example, does not need to expend power maintaining a list of the addresses of the devices it is expected to turn on and off. Instead, it publishes a "turn on" message marked for the attention of the "kitchen lighting" list. The message is relayed around the mesh and devices decide for themselves whether to act on it based on whether or not they subscribe to the list.

The other way relies on energy-constrained devices calling a "friend". Temperature sensors, for example, might not be required to send out regular readings, but only to report when the temperature drifts outside a set range. That saves energy on the transmission side, as the sensors only have to signal rare exceptions -- but constantly listening for updates to the set temperature range can soon flatten batteries. By designating a device with plentiful power as their friend, such sensors need only turn on their radio receiver once a day (or whatever interval has been agreed), at which point their friend hands over all the messages sent to them while they've been offline. It's a little like having someone pick up your mail for you while you're on vacation, rather than running home every day to check your mailbox.

Choosing which mesh network to join, or which devices to be friends with, will be a little more complicated than pairing two Bluetooth devices to make a point-to-point connection.

The process, called provisioning, will require an app running on a Bluetooth-enabled smartphone, tablet or computer. New mesh devices, be they lightbulbs, industrial sensors or security cameras, will arrive unprovisioned, and will need to download encryption keys from the app to join the network as a node.

Those keys can be revoked using the same app, making it possible to safely dispose of a broken smart lightbulb, say, without the risk that a determined dumpster diver might recover the keys from the discarded bulb and use them to subvert the entire network.

The spec's developers have also taken care to protect Bluetooth mesh networks against replay attacks by ensuring each message has a unique sequence number.

The spec also provides different encryption layers for the network infrastructure and the applications that run over it. This means that a hotel's smart lighting network could carry a message to a hotel room door telling it to unlock -- but only the hotel's smartphone app, say, would hold the encryption keys necessary to generate the message in the first place.  

The introduction of mesh networking will help Bluetooth overcome some of its existing limitations on range and network size, according to Andrew Zignani, a senior analyst at ABI Research.

"Mesh networking represents a new phase in Bluetooth's evolution and will be a critical enabler of its transition from a personal area network and pairing technology towards a more scalable, robust, low-power IoT connectivity solution with the ability to connect to the things around us," he said via email. 

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