📬 What is Publish-Subscribe?

Imagine a radio station. The station broadcasts (publishes) music on a frequency. Anyone who tunes in (subscribes) to that frequency can hear it. The station does not need to know who is listening.

Bluetooth Mesh works exactly the same way. A node publishes messages to an address. Any node that has subscribed to that address receives and acts on the message.

The switch publishes once → all three subscribed devices receive it

📍 Address Types in Bluetooth Mesh

Bluetooth Mesh has three types of destination addresses. Choosing the right one determines who receives a message.

↩️ Two Kinds of Messages

When a model sends a message, it falls into one of two categories:

🏠 Multiple Subscriptions — The Bedroom Light Example

A node can subscribe to more than one group address. This is very useful for smart home scenarios where one device belongs to multiple logical groups.

Now the bedside light will respond to any of these commands:

• “Turn off bedside light” → targets 0xC001 → only bedside light responds
• “Turn off bedroom” → targets 0xC002 → all bedroom lights respond
• “Good night” → targets 0xC004 → ALL lights in the house turn off

🔢 Sequence Numbers & Replay Attack Protection

Every message in Bluetooth Mesh is sent from a single unicast address (element address) and includes a unique sequence number. This sequence number increases with every message sent.

💻 BlueZ in Action — Setting Up Publish & Subscribe

Using mesh-cfgclient, you can configure a node to publish and subscribe. Here is how to set up our power strip sockets:

Step 1: Subscribe Socket 1 to a group address

# Subscribe element 0x0001 (Socket 1) to group 0xC001 ("All Sockets")
# Command: sub-add <node_addr> <element_addr> <group_addr> <model_id>
[mesh-cfgclient]# sub-add 0x0001 0x0001 0xC001 0x1306

# Output: Subscription added for model 0x1306 on element 0x0001

Step 2: Configure Socket 1 to publish its status

# Set publish address so Socket 1 reports its state to group 0xC002
# Command: pub-set <node_addr> <element_addr> <pub_addr> <app_key_idx> <ttl> <period> <count> <model_id>
[mesh-cfgclient]# pub-set 0x0001 0x0001 0xC002 1 5 0 0 0x1306

# Now element 0x0001 will publish power level status to 0xC002

Step 3: Also subscribe Socket 1 to the “Whole House” group

# A node can have multiple subscriptions on the same element/model
[mesh-cfgclient]# sub-add 0x0001 0x0001 0xC010 0x1306
# Socket 1 now responds to messages sent to 0xC001 OR 0xC010

Step 4: Send a power level message to all sockets (group 0xC001)

# Set destination to group address
[mesh-cfgclient]# dst 0xC001

# Send Generic OnOff Set — turn all sockets OFF
# Both Socket 1 (0x0001) and Socket 2 (0x0002) will respond
# because both are subscribed to 0xC001
[mesh-cfgclient]# onoff-set 0 0x01

# Output:
# Generic OnOff Set sent to 0xC001
# Received OnOff Status from 0x0001: state=OFF
# Received OnOff Status from 0x0002: state=OFF