🏠 What is a Node?

A node is any device that has been added (provisioned) into a Bluetooth Mesh network. Before provisioning, a device is called an unprovisioned device. Once it joins, it becomes a node.

Examples: Smart power strip, smart bulb, temperature sensor, light switch.

💡 Key insight: A single device can have multiple elements. Each element gets its own unicast address so it can be controlled independently.

🔌 What is an Element?

An element is a logical part of a node that can be independently addressed. Think of it as a sub-device inside a device.

Why do we need elements? Because in our power strip, the two sockets are independent. You need to turn on Socket 1 without affecting Socket 2. So each socket is modelled as a separate element with its own address.

📦 What is a Model?

A model defines the functionality of an element. Every model has two things:

Models are standardised by the Bluetooth SIG. That is why a dimmer from Brand A can control a bulb from Brand B — both implement the same model.

Models in our power strip example:

🖼️ Element-Model Structure: Dual Socket Power Strip

Here is how the full dual-socket device looks with both elements side by side:

Both sockets have identical models. Only the primary element (Socket 1) also carries the Configuration Server.

🔗 State Binding — The Clever Trick

Here is a very powerful feature. Imagine a dimmer switch. The dimmer does not know anything about power strips. It only knows how to set a generic level (0% to 100%). Yet it can control our smart power strip! How? Through state binding.

The Generic Level state is bound to the Generic Power Actual state. When the dimmer changes the Generic Level, the binding automatically changes the Generic Power Actual — and the socket adjusts its power output. No extra logic needed!

💻 BlueZ in Action — Reading Element & Model Info

The BlueZ stack ships with mesh-cfgclient, a command-line tool to interact with Bluetooth Mesh nodes. After provisioning a node, you can read its composition data — which tells you all its elements and models.

Step 1: Launch mesh-cfgclient and connect to the daemon

# Make sure bluetooth-meshd is running
sudo systemctl start bluetooth-meshd

# Launch the mesh configuration client
mesh-cfgclient

Step 2: Read the node composition (elements + models)

# Target the node by its unicast address (0x0001 = first node)
[mesh-cfgclient]# target 0x0001

# Request composition page 0 — this lists all elements and their models
[mesh-cfgclient]# get-composition 0

# --- Expected output ---
# Received Composition:
#   CID: 0x05F1  PID: 0x0001  VID: 0x0001  CRPL: 10
#   Features: Relay Proxy Friend LPN
#
#   Element 0  (addr: 0x0001)   <--- Primary Element
#     SIG Model: 0x0000  (Configuration Server)
#     SIG Model: 0x0002  (Health Server)
#     SIG Model: 0x1306  (Generic Power Level Server)
#     SIG Model: 0x1100  (Sensor Server)
#
#   Element 1  (addr: 0x0002)   <--- Secondary Element
#     SIG Model: 0x0002  (Health Server)
#     SIG Model: 0x1306  (Generic Power Level Server)
#     SIG Model: 0x1100  (Sensor Server)

What are those hex model IDs?