Bluetooth mesh networking FAQs

Message relay questions

Why did Bluetooth choose a flood-based message relay approach?

A managed flood approach to message relay best meets the requirements for enabling simple, reliable and scalable mesh networks.

With managed flood messaging, no complex routing table creation and management is required. Even in routed solutions, where a table can be automatically generated, significant network interruptions can occur.

Managed flood messaging is inherently multipath, ensuring messages reach their intended destination. It’s also inherently peer-to-peer, allowing all nodes to communicate directly with one another. With no central hub or routing nodes, there are no single points of failure.

In most mesh network implementations, a significant percentage of messaging traffic is multicast, such as a single light switch in a building that controls tens or hundreds of lights. The managed flood messaging approach of Bluetooth mesh, combined with its publish/subscribe group messaging model, supports extremely efficient messaging for large-scale networks with high performance.

Are all flood-based mesh networks power inefficient?

No, in a simple flood-based mesh network that can be the case, but Bluetooth technology implements a managed flood approach in which only main-powered nodes serve as message relays. Low-power nodes, such as battery-powered sensors, are not responsible for message relay. In a Bluetooth mesh network, low-power nodes with a coin-cell battery can operate for many years.

How does Bluetooth mesh networking handle multicast messaging?

Bluetooth mesh handles multicast communications using a publish/subscribe group messaging approach.

Half of the address space is allocated to group addresses, and a message can be sent to a group address. Each node can be configured to subscribe to a set of group addresses and publish messages to a set of group addresses.

For example, a light switch may publish the “turn on” message to the “hallway group”, and all lights along that hallway would be subscribed to that same “hallway group” address. But the lights may also be subscribed to other groups, such as the “ground floor group”, the “all lights group”, and the “emergency exit route” group.

Bluetooth mesh also supports virtual addresses, which extend group addresses by allowing a 128-bit UUID to act as the destination address. A hash of the Label UUID is used to reduce the overhead of checking UUIDs. Each hash value represents millions of different Label UUIDs, increasing the number of potential virtual addresses.

Provisioning Questions

What is provisioning?

Provisioning is the process of adding a device to a specified mesh network. It turns a device into a node on the network and includes security key distribution and the creation of a unique ID for the device being added.

Can I back up my provisioning data and restore it?

Yes, you can back up your provisioning data. This is not defined in the specification, so you can use any backup mechanism you like.

General Architectural Questions

What is a node?

A node is a provisioned device on a Bluetooth mesh network.

How many nodes can I have in a single network?

While the spec allows for up to 32,000 nodes to be provisioned, we don’t expect those numbers to be achieved quickly in the real world. However, we are already seeing representative networks exceeding well over 1,000 nodes, which is much greater than other low power mesh technologies on the market today.

Do I need different types of nodes for a Bluetooth mesh network?

No, unique to Bluetooth mesh networking, all nodes in a network are decentralized and can talk to each other directly.

There are no centralized hub or routing nodes, so there is no single point of failure. However, to accommodate low-power nodes, such as battery-powered sensors, only some nodes perform the message relay function.

Some nodes take on additional functions to support messaging to low-power nodes. This allows a low-power node to remain part of a network, but it can sleep for hours or days at a time until it needs to report some bit of information. As a result, low-power nodes using a coin-cell battery can operate for many years.

What are models and properties?

Bluetooth adopted a simple, yet powerful approach for developers to describe what a node on a Bluetooth mesh network is and does so that it can interact with other nodes. This approach is based on a set of building blocks called models. Models consist of a collection of features with defined functions and behaviors.There are four classes of models, including generics, sensors, timing and lighting. Generic models are the basic building blocks and define the standard functionality of a device, such as the ability to have a simple on/off state. You can combine generic models or enhance them using properties. Properties provide additional context and value to a model.

Security Questions

How is security handled in a Bluetooth mesh network?

Bluetooth mesh networking is a true industrial-grade solution, including its approach to security.

• Devices added to a network are provisioned using proven security algorithms. This uses 256-bit elliptic curves and out-of-band authentication to securely add devices.
• All communication is required to be secured using AES-CCM using 128-bit keys. All mesh messages are encrypted and authenticated.
• Encryption and authentication are applied at two layers, the network layer and the application layer. All nodes in the network help relay messages at the network layer without being able to read their contents. Those contents are secured with a separate application key, providing true end-to-end security.
• Each message has a minimum of 64 bits of authentication, but it’s possible to have up to 1088 bits of authentication for the longest messages.
• Models are organized in the specification to account for different users with different security credentials. This gives maintenance personnel full control over network configuration while allowing employees to interact.
• Replay attacks are prevented by mandating fresh sequence numbers on every message sent.
• Devices can be blacklisted in the mesh network by using defined key update procedures. During provisioning, each device computes a unique device key that only the provisioner knows and can update.
• Messages protect identify by obfuscating every packet sent and refreshing privacy. This means that even if you carry mesh devices on you while walking around, people sniffing mesh packets cannot track you.

What kinds of security attacks is Bluetooth mesh networking designed to prevent?

• Brute-force attacks are prevented by using 128-bit keys, and a minimum of 64-bit authentication on every single packet.
• Replay attacks are prevented by using fresh sequence numbers of every packet sent and checking those on every packet received.
• Man-in-the-middle attacks are prevented using ECDH cryptography during provisioning with out-of-band authentication.
• Trashcan attacks are prevented using a key-refresh procedure, allowing keys in all remaining devices and blacklisting the removed/broken devices. Should someone disassemble a thrown-out device, it can’t reveal any security information.
• Physically insecure device attacks are prevented by allowing devices in an insecure location to have separate keys to those in a physically secure location. This prevents someone from attacking a door bell and sending a message to unlock the door.
• Visitor attacks are prevented by giving guests and visitors temporary and limited access to the network using a separate set of keys. These guest keys have a limited lifetime.

Do I lose privacy when using a Bluetooth mesh network?

No, every mesh packet is obfuscated to protect the user’s identity. An attacker listening to mesh packets cannot determine which device sent that message since there are no identifying values, such as the source or destination address. Each time a message is relayed, this obfuscated information is changed, removing the ability to track message flow.

What happens if my neighbors also have a Bluetooth mesh network?

Each mesh packet includes a small identifier that determines which network the mesh packet belongs to. A device in one mesh network can’t decrypt or authenticate mesh packets from another mesh network, and it will never relay those messages. Each mesh network is completely isolated.

Reliability Questions

How do I know if nodes on my Bluetooth mesh network stop working?

Nodes on a Bluetooth mesh network send out a heartbeat message. In addition, there is a mandatory Health model that allows devices to send out fault information. For example, if a device overheats, it sends an “overheating fault” message.

Is traffic affected if nodes break?

No, nodes relaying messages that stop working will not stop the network. Flood message relay creates an inherently self-healing network, as messages are sent through multiple routes at the same time.