The Bluetooth Special Interest Group (Bluetooth SIG) introduced a standard for wireless data transfer in the year 2000: Bluetooth Basic Rate (BR)/Enhanced Data Rate (EDR). In 2010, Bluetooth SIG further enhanced its standard with the definition of Bluetooth Low Energy (BLE), which made data transfer possible with low power consumption.
The demand for this wireless communication technology is high, also because further improvements and developments can be expected. The success of BLE is first and foremost due to its very low power consumption. But the BLE protocol also has its disadvantages. Only three types of communication are possible: Between two individual devices (point-to-point communication, bidirectional, 1:1, Image 1), between one device and many others (one-to-many communication, bidirectional, 1:m, Image 2) or communication in which the data from one device is continuously sent to the environment without having a specific addressee (broadcast communication, Image 3). When broadcasting, all BLE devices in the environment can receive the data but cannot respond to it. The disadvantage of these network topologies is that the entire network fails if the master (star configuration, central role) that is to transfer the data fails.
The perfect network technology
In July 2017, Bluetooth SIG introduced Bluetooth mesh, a further improved wireless communication technology based on the Bluetooth Low Energy communication protocol which can be used optionally. With Bluetooth mesh, a large network of many-to-many connections (m:m, Image 4) can be established across a large physical area with up to 32,000 network participants. Transfer still works even if the device that originally sent the message is not in the direct radio range. In addition, Bluetooth mesh 1.0 network technology enables communication between devices from different suppliers, which was not possible with previous proprietary solutions, such as CSRmeshTM. Further advantages are robust and secure data transfer as well as very high energy efficiency.
These features make Bluetooth mesh a perfect network technology for many areas of application, such as building automation, sensor networks, industrial manufacturing or goods tracking. Generally speaking, Bluetooth mesh is suitable for all applications that require communication between several devices with a minimum of data.
How does Bluetooth mesh work?
Bluetooth mesh works with a messaging system in which messages are distributed according to the publishing and subscribing principle. Sending messages to a device with a specific address is called publishing. Subscribing is the configuration of devices for which a specific address is assigned to the device. This device can then only receive messages if they have been sent to the specific address. An example: Hall lighting is installed with Bluetooth mesh. All the light bulbs are configured to receive the "hall lighting" subscription. If the "on" message is sent to the "hall lighting" address via a BT mesh switch, all the light bulbs registered under "hall lighting" are switched on.
Data transfer in Bluetooth mesh is referred to as "flooding". This means there is no special route for the message through the entire network to the slave (receiver). The message is sent to all devices within range and then forwarded until it reaches the correct slave.
Due to a dense number of network participants, it is possible to overcome obstacles which previously required the use of slower and not globally standardized sub-GHz technology. Even if the device that originally sent the message (master) is not within radio range, the message still reaches the correct slave. If the network is already narrow enough due to the participant density, connections can be secured redundantly, which is why the data would still find their destination even if a single participant would no longer function as a relay. This self-healing property makes Bluetooth mesh one of the most reliable networks and ensures its wide-scale use in industry for the first time.
The devices in a Bluetooth mesh network are called nodes. There are four different types of nodes that - in addition to sending and receiving - deliver additional functions:
- Relay nodes: They forward received messages to the next device. Message transfer functions using so-called "hops", with Bluetooth mesh supporting a maximum of 127 hops.
- Low-power nodes: Some devices, such as sensors, need to be extremely energy-efficient. Low-power nodes work in conjunction with one or more other nodes called "friends".
- Friend nodes: Sufficient energy is available here, e.g. through connection to the mains supply. These friend nodes work together with low-power nodes. Friend nodes store messages and forward them only when requested to do so by the low-power node.
- Proxy nodes: They provide the GATT interface (generic attribute profile) for BLE devices without the Bluetooth mesh stack. This also enables communication between BLE mesh and a normal BLE node.
Within the access layer of the OSI layer model, it can be determined whether a confirmation message (acknowledgment) should be sent back to the master after receiving the message or not.
Is Bluetooth mesh secure?
Setting up a large network with many devices poses a huge risk to secure data transfer. Security was therefore the top priority when developing Bluetooth mesh. To this end, Bluetooth SIG outlines a strict specification. All security functions within a Bluetooth mesh network are mandatory.
However, the security vulnerability in Bluetooth Secure Simple Pairing and LE Secure Connections identified by researchers at the Israel Institute of Technology also affects Bluetooth mesh, as it is based on the BLE stack. Some suppliers with affected products already offer a firmware update or are in the process of fixing this problem. Rutronik has compiled an overview of the affected Bluetooth products from the line card to record the status of possible firmware updates: https://rutronik-tec.com/bluetooth-security-vulnerability-status/
- The key security features are: · Encryption and authentication: All Bluetooth mesh network messages are encrypted and authenticated.
- Separation of concerns: There are three different security aspects within a Bluetooth mesh network: Application, network, and device security. They are handled independently of each other and have their own security keys:
- Application key (AppKey): This secures data relating to specific applications, e.g. lighting or cameras.
- Network key (NetKey): Network keys apply to all devices in the network, thereby ensuring secure data transfer.
- Device key (DevKey): Each node has a unique device key. This security key can be used to add devices to a network.
- Area isolation: The Bluetooth mesh network is divided into subnets. These subnets are each cryptographically distinct and secure from the others.
- Key refresh: All security keys can be changed in the Bluetooth mesh network during a key refresh procedure. · Message obfuscation: This data privacy mechanism makes it extremely difficult to track nodes in a network. It is therefore almost impossible to track messages sent.
- Replay attack protection: Security functions protect the network against replay attacks (previously collected data is used for authentication and access control → identity theft). · Trashcan attack protection: Nodes can be removed from the network securely in a way that prevents trashcan attacks (reading important network information from invalidated nodes).
- Secure device provisioning: New nodes can be added to the Bluetooth mesh network in a secure process.
All these extensive security features make Bluetooth mesh an interesting solution for applications that require low data rate communication between multiple devices. In addition, Bluetooth mesh is ideal for new areas of application such as predictive maintenance or smart agriculture/farming. Implementation of a wireless sensor mesh network in assembly lines can warn maintenance staff in good time before a machine fails. Or, by using mesh networks in agriculture, data such as soil and air humidity or temperature can be transferred directly to a smartphone without a gateway. It also allows more efficient use of water and fertilizers and reduces the use of pesticides: Appropriate measures are only taken if the measured values fall below a certain limit. In the smart home sector, lights could be equipped with sensors that register when someone is nearby, ensuring the lights are only switched on in this case. Bluetooth mesh could even be used for sporting activities: Sensors integrated in the athlete's shoe can record performance data, which can then be transferred via a Bluetooth mesh master from one athlete to the next until they reach the coach, for example, who can then evaluate the data. Another advantage: The actual environment is not important for BLE mesh technology. Innumerable applications are conceivable due to the industrial requirements fulfilled by mesh specification 1.0 and higher: Be it in hospitals, factories, offices, universities or private homes. Bluetooth mesh is well worth a closer look wherever wireless, secure, and robust communication between a large numbers of devices enables new applications.
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